[HN Gopher] Everything you need to know to design your own CNC r...
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Everything you need to know to design your own CNC router
Author : mferraro89
Score : 300 points
Date : 2021-01-19 02:35 UTC (20 hours ago)
(HTM) web link (mattferraro.dev)
(TXT) w3m dump (mattferraro.dev)
| YZF wrote:
| I designed and built my own CNC router from scratch about 10
| years ago. I just recently got it out to play with... Fun. But
| boy does it make a lot of dust to cut wood with a router (which
| is mostly why it's been sitting in the garage for so long, plus
| not a lot of time, plus it's not a very practical one, small work
| area).
|
| EDIT: Random tidbit is that I control it from an old PC's
| parallel port. The PC runs DOS (the best real time OS ;) ) and
| uses some old free software called TurboCNC that can read G code
| and drive step and direction drivers. It has it's limitation but
| if you have an old PC around...
| mferraro89 wrote:
| Very cool! A modern analogue might be LinuxCNC, which runs on
| old PCs in a realtime manner, generating pulses and sending
| them out the parallel port, or sending commands over ethernet
| to a dedicated step generator board for ultra accurate timing.
| What's old is new again!
| YZF wrote:
| I wanted to check it out at some point though I'm a little
| scared about the ability of Linux to pulse step and direction
| with the same precision of a 15 year old DOS setup that has
| no background tasks and just hits that timer interrupt with
| very predictable result... The motion generation capabilities
| of TurboCNC are pretty basic though.
|
| Btw, if anyone is interested that build is documented here:
| https://www.cnczone.com/forums/diy-cnc-router-table-
| machines...
| craftinator wrote:
| I run LinuxCNC on a Raspberry Pi 4, and it works wonders.
| LinuxCNC is installed with a realtime Linux kernel; it'll
| run just as realtime as DOS.
| tabulatouch wrote:
| I tried as well but found no guides to build a RPi4
| LinuxCNC machine with realtime. Can you point me to some
| tutorial or ready SD card image?
| craftinator wrote:
| I'll go through my saved links tonight. I remember it was
| a bit of a cludgy operation, like all things new+Linux,
| but after I got everything setup it all worked as
| expected.
|
| I think this forum post pointed me in the right
| direction: https://www.forum.linuxcnc.org/18-computer/368
| 79-raspberry-p...
| jacquesm wrote:
| If you can, _please_ use servos and not steppers. Steppers are
| cheap and ridiculously easy to interface and get good positional
| control out of. As long as they don 't skip steps. And they
| _always_ do. So you end up running at 1 /10th of the speed your
| tool could move at to avoid that, and even then you'll end up
| tossing workpieces because you lost synchronization somewhere
| along the line.
|
| For 3D printers they work fine because there is no pushback
| ('loading') from the extruder. But for anything that cuts servos
| are the way to go if you want half decent speed and quality cuts,
| as well as long tool life.
| justinclift wrote:
| > So you end up running at 1/10th of the speed your tool could
| move at to avoid that ...
|
| Doesn't that only happen when the controller either doesn't
| know (or can't decently handle) the limits for a given machine?
|
| eg if a machine could (say) only accurately (without losing
| steps) push the spindle at 1000mm/min, with maximum jerk of
| (say) 0.5
|
| If your controller doesn't know to keep in those limits... it
| makes sense steps will be lost when going past those limits.
|
| So, seems more like a tuning problem?
|
| That being said, closed loop stepper systems exist, though I
| haven't (yet) personally tried them.
| numpad0 wrote:
| I long had dimensional accuracy issue that the whole axes
| seemed to stretch and contract like 5%, on a cartesian 3D
| printer, and it just _went away_ after I switched to Servo42B
| setup.
|
| I think it's microstepping. Steppers with microstepping
| enabled and controlled by an 8-but micro must be assumed to
| produce zero holding torque and assumed they always miss a
| step or two.
| jbay808 wrote:
| Microstepping does not reduce torque in any respect.
| craftinator wrote:
| Upgrade the controller. For a hobbyist machine, the ESP32
| CNC controller sold on Tindie is well suited to deal with
| that, and costs ~$35.
| StavrosK wrote:
| I made a PCB for an ESP32 CNC controller, if anyone finds
| it useful:
|
| https://gitlab.com/stavros/esp32-cnc
| craftinator wrote:
| Nice! I'll check it out! Here's a link to the one I'm
| using:
|
| https://www.tindie.com/products/33366583/grbl_esp32-cnc-
| deve...
|
| The developer is really responsive, might be worth
| collaborating since you have put in similar work.
| dekhn wrote:
| There are several newer boards from Bart (including the
| 6-pack which has some add on modules).
|
| Grbl ESP32 is great. Easily the best of the firmwares
| I've used so far.
| craftinator wrote:
| I've been interested in upgrading to his newer boards,
| but I'm not sure I want the added complexity at the
| moment. Have you used the generic modular one? If so, how
| does it compare to the older one I linked to?
| dekhn wrote:
| Interesting question; I just had to go through this
| myself. I really only wanted 3 axes and considered the
| older one you linked to (which isn't marked 'retired',
| but is "out of stock"). The first thing I'd mention is
| that the older board doesn't support the new style of
| drivers (old = TI DRV8825, new = Trinamic SPI). SPI
| drivers are much nicer for a number of reasons, in
| particular you can change the motor current via software,
| and with the trinamics there's support for stallguard.
|
| In my case I'm not building a CNC, but controlling the
| axes of a microscope (X, Y, Z) plus the intensity of the
| illuminator and likely several other things, so the
| 6-pack (which I also use on my CNC) had what I wanted.
|
| Oh, you can also use either onboard or external motor
| drivers with the 6-pack- external motor drivers are good
| for NEMA23 and other large motors.
| PragmaticPulp wrote:
| I think he's exaggerating for effect. Properly sized steppers
| have more than enough margin for rapid movement on hobby
| machines without losing steps ( Video example at 1000ipm:
| https://www.instagram.com/p/B1wSmXfnm6C/ ).
|
| Skipped steps are only a problem if the machine is tuned
| wrong, like you said, or the steppers are too undersized to
| keep up.
|
| People tend to underestimate the strength of common NEMA23
| steppers while overestimating the cutting forces they need.
| Most hobby machines don't have enough rigidity or spindle
| power to require more than a few pounds of lateral cutting
| force.
| YZF wrote:
| To be precise, it's not the strength of the stepper, it's
| the gearing through the screw that converts the torque of
| the stepper into the force on the tool.
| jacquesm wrote:
| And that will give you slop which will translate into
| imprecise workpieces and surfaces that aren't flat.
| PragmaticPulp wrote:
| At the hobby CNC level (what's being discussed in this
| article), the rigidity of the machine is far more of an
| issue.
|
| I think your advice is spot-on if someone was designing a
| 5000lb vertical mill out of steel, but hobbyists building
| DIY bench top machines face a different set of problems.
|
| Hobby level machines are almost always limited by
| rigidity, not movement motor torque.
| jacquesm wrote:
| I've built a whole pile of CNC machinery, both
| lightweight and heavyweight. If you don't actually care
| about what you produce, fine, go with open loop steppers.
| If you want to control a device that produces accurate
| work products that do not need extensive rework (or to be
| tossed) then use something with a feedback mechanism.
|
| I'm fine with you advocating for steppers for non-contact
| or drawing work (laser cutters, engraving and so on). But
| if you care about your tools, you don't want to wait for
| hours for what should be a small job then add the bit of
| money for a servo or a hybrid solution, on the total cost
| of the machine it won't make a lot of difference and the
| machine will be so much more reliable and faster that
| you'll end up using it much more frequently.
|
| Right tool for the job and all that, bench top CNC with
| small servos is a very powerful tool in the hobbyists
| arsenal, and if you scrounge ebay you'll find they can be
| quite affordable. Note that anything that cuts has a
| stand-time, and if you move slower or make many passes
| because you can't really cut then you will end up
| spending a fortune in tooling which at some point will
| easily outweigh the price of the feedback mechanism,
| which automatically compensates for increased load and
| toolbit wear.
| jacquesm wrote:
| > I think he's exaggerating for effect.
|
| I wasn't. You'll never make it through your first resonance
| point without current feedback, and a good stepper driver
| can easily go into very large multiples of that frequency.
|
| Then there is microstepping.
|
| > Most hobby machines don't have enough rigidity or spindle
| power to require more than a few pounds of lateral cutting
| force.
|
| This is true, but a different problem.
| PragmaticPulp wrote:
| I think you're approaching this discussion from a
| commercial/industrial scale.
|
| Hobbyist CNC machines simply don't have the same issues
| as large commercial-grade CNC mills. None of the popular
| hobby CNCs use closed loop motor control. Skipped steps
| are simply not an issue at this scale.
| jiveturkey wrote:
| tormach doesn't seem to have a problem with it. it's only
| recently they started offering servo upgrades.
| PragmaticPulp wrote:
| > Steppers are cheap and ridiculously easy to interface and get
| good positional control out of.
|
| This is exactly why 99% of beginners should start with stepper
| motors.
|
| Building a CNC is an exercise in tradeoffs. It's tempting to
| want to choose the best option at every juncture, but that's a
| recipe for blowing your budget. I strongly recommend that
| beginners start with sufficiently-large stepper motors to get
| things done, then consider more expensive motors as a later
| upgrade.
|
| > As long as they don't skip steps. And they always do. So you
| end up running at 1/10th of the speed your tool could move at
| to avoid that
|
| They definitely don't always skip steps. I've never skipped
| steps on my hobby CNC during normal operation. Only crashing
| the machine causes skipped steps, at which point I have bigger
| problems to worry about.
|
| It's very easy to measure the maximum force your stepper-based
| CNC can apply before skipping steps. You can use a common
| kitchen scale and manually force the CNC axis to compress the
| scale until it skips.
|
| In my case, the maximum stepper force is about an order of
| magnitude higher than the calculated cutting forces in
| aluminum. If someone was trying to push the cutter so hard that
| it was overwhelming common NEMA 23 steppers, they're going to
| need an extremely rigid machine. Most hobby-level machines
| aren't rigid enough to use high cutting forces, and unless you
| have a 2.2KW water-cooled spindle, you won't have enough power
| to cut at those speeds anyway.
|
| As long as your steppers are sized appropriately, it's really
| not a big deal.
|
| > So you end up running at 1/10th of the speed your tool could
| move at to avoid that
|
| Again, not really an issue in practice. Use sufficiently-sized
| stepper motors and the movement speed is just fine.
|
| I strongly suggest that anyone building a CNC focus first and
| foremost on keeping it simple and cheap. Get it built, learn
| from the process, and improve on your next iteration. Closed-
| loop stepper motors are a reasonable upgrade path, but the idea
| that you're going to be skipping steps with regular steppers
| just isn't true.
|
| EDIT: Here's a video of a common Shapeoko with significant
| added weight moving at 1000ipm on the tiny stock steppers
| without issues: https://www.instagram.com/p/B1wSmXfnm6C/ The
| stock settings are 200ipm, which leaves ample safety margin for
| normal operation. 200ipm is plenty fast for rapids unless
| you're trying to reduce cycle times on large-scale
| manufacturing, in which case you wouldn't be using a hobby CNC
| machine.
| taneq wrote:
| All of this is spot on.
| CamperBob2 wrote:
| What do you think of these? https://www.crowdsupply.com/iq-
| motion-control/iq-motor-modul...
| jacquesm wrote:
| For their size those are very impressive, I'd be quite
| concerned about cooling them but there must be applications
| where their form factor would be a game changer.
| justinclift wrote:
| Looks like the wrong kind of thing? Those seem to be high
| speed drone motors.
|
| Am thinking they'd not have enough torque, unless you gear
| them pretty high.
| CamperBob2 wrote:
| Further down the page, they explicitly call out CNC
| applications. ("IQ motors are smoother, quieter, and more
| efficient than stepper motors, and they will never skip a
| step or get lost.")
|
| They are basically a stepper motor from the application's
| point of view, but with some of the advantages of a servo,
| as far as I can tell.
|
| (No affiliation, just curious if these guys are onto
| something useful.)
| gji wrote:
| Just judging by the torque specs and comparing to a
| nema23 stepper, seems like it needs an order of magnitude
| more torque to compare. Note that in the comparison chart
| they compare to a nema11, which is tiny compared to the
| steppers used in most hobby cncs.
| taneq wrote:
| > As long as they don't skip steps. And they always do. So you
| end up running at 1/10th of the speed your tool could move at
| to avoid that, and even then you'll end up tossing workpieces
| because you lost synchronization somewhere along the line.
|
| My experience has been roughly opposite of this. If you
| overload your motors, you're going to lose positional accuracy
| and probably wreck your workpiece regardless of whether you use
| steppers or servos. If you don't overload your motors then the
| difference is moot, and with steppers there's less to go wrong.
| PragmaticPulp wrote:
| In practice, hobby CNC machines use the closed-loop feedback
| systems to halt the machine and alert the operator that
| something has gone wrong.
|
| Hobby-scale machines shouldn't need closed-loop systems for
| positioning during cutting operations. Especially if they're
| using a 300-400W (sustained) consumer router as their spindle
| as this article suggests.
|
| Cutting forces at this scale are in the single-digit pounds.
| Nothing a common NEMA23 can't handle with plenty of margin.
| Trying to push a low-powered spindle through the workpiece on
| a low-rigidity hobby machine causes more problems.
| devwastaken wrote:
| Have any recommendations on servos for this purpose?
| jacquesm wrote:
| Ebay. That's by far the best place to spot really good gear
| for a small fraction of the sticker price.
|
| The usual suspects for brands, personal favorite: Panasonic
| Minas series drivers + associated servos. Cheap, super
| reliable and available in just about every size that you
| could possibly want.
| formerly_proven wrote:
| I've looked into this a few times and it always seemed like
| there is a huge abundance of servo motors, but the market
| for servo amplifiers seems to be tiny in comparison. I
| always suspected this is because the electronics of
| decommissioned machines are just scrapped wholesale.
| However, I am also wondering what people are doing with all
| these servo motors without matching cabling and amplifiers.
| jacquesm wrote:
| Good point, amps are a bit harder to get by than motors,
| but then again, there are plenty of them on offer. I only
| paid full price once for a set of servo amps and that was
| because I wanted to have a particular type for a very
| special set of motors (pancake servos).
| mferraro89 wrote:
| OP here: Teknic Clearpath servos are considered good value
| and come in lots of different sizes/price points. Wiring them
| up could not be simpler, but know that you need a windows
| computer to tune them.
|
| If you are comfortable with soldering, motor sizing, and
| python, you can pick up an ODrive control board and some sort
| of position sensor and turn almost any motor into a servo
| motor.
| craftinator wrote:
| I've purchased a couple of these for UT CNC systems;
| definitely good bang for your buck, but that's if you need
| to drive a 1200 lb bridge at 6 in/s, and have $600 per
| motor to spend.
|
| I ended up not using them because I found it was simpler,
| cheaper, and fit the mounts better to buy a pack of NEMA34
| steppers and a few $15 dollar encoders. Seriously, spent
| maybe $800 on decent quality steppers/encoders/amps for 3
| axes, where the ClearPath servos would have been $1600 for
| the same 3 axes, but wouldn't have provided position
| feedback nor allowed position localisation to be decoupled
| from the motors (which is the best way to do things in most
| cases).
|
| I think it's hard to justify the costs of these types of
| motors unless you have some very specific
| torque/speed/spacial requirements that require them. If
| you're building a machine that is worth >$4000 per axis,
| then maybe, but if not, simple steppers are the way to go.
| augustt wrote:
| https://odriverobotics.com/
| craftinator wrote:
| Or just use a gear reduction? You really need to be dealing
| with high force systems to justify the cost and added
| complexity of using servos. I've built a mill from scratch that
| can handle decent sized steel milling using NEMA23 sized
| steppers and some decent 10:1 gear reducers and a nice spindle.
| IMO a better spindle and structure is where you should be
| spending your money, and if you really are afraid of losing
| steps, you should use encoders that are DECOUPLED from the
| motors, not integrated into them...
|
| Servos are great if you're working with huge forces, need a lot
| of speed, need ridiculously high accuracy, and have a team of
| engineers to actually build and tune the thing. Ridiculously
| expensive and complex unless you're looking to go into busines
| manufacturing CNC systems.
| jacquesm wrote:
| Gear reduction gives you slop, if you need to reduce the
| better way is probably using a kevlar toothed belt and two
| pulleys. Still not perfect but better than gears. Finally,
| the best way (and most expensive way) is by using a properly
| pre-tensioned ball bearing driven spindle ('ball screw').
| craftinator wrote:
| I work in the non-destructive testing industry, testing
| aerospace parts. We build CNC testing rigs fairly
| regularly, with x and y axes longer than 30 feet, and carry
| loads of >1000 lbs. These need to be able to center on
| holes with diameters of <1 mm, because that's what we
| calibrate our equipment on.
|
| The most reliable build setups we have are kevlar belts
| coupled with 16:1 reduced stepper motors, and decoupled
| encoders that index using constant pressure rack and
| pinions. Even pre-tensioned ball screws give us enough slop
| to be a problem without encoders, and kevlar belts are an
| order of magnitude cheaper; going with a reduced stepper vs
| a servo takes the cost down by half.
| jacquesm wrote:
| Ah good point, yes, at those lengths you really don't
| want ballscrews, they are impossible to support and will
| warp. But for short distance (up to 8' or so) with a
| support on either end they are fine.
| craftinator wrote:
| Yeah, my brain is kinda tuned to those long distances. I
| also kind of harp on people who say they need really high
| precision systems, so use servos and spend bookoo bucks
| on slop-reductive hardware.
|
| Even a cheap encoder, when decoupled from the motor, and
| directly coupled to the axis it measures, will give
| better axial positioning than a servo. It boggles my mind
| why people seem to ignore this in favor of a motor that
| knows where it is in space, but doesn't know where the
| axis it is driving is in space.
| traverseda wrote:
| Stepper motor drivers that support stallgaurd (trinamic's
| stepper drivers) seem like the best of both worlds, and even
| in-theory can give you some force feedback.
| SV_BubbleTime wrote:
| As someone with a CNC router with steppers I can not agree
| more.
| gorkish wrote:
| You might be able to interface Mechaduino or MKS controllers
| between your steppers and drivers to make them pesudo-closed
| loop. They still get driven by step+dir however the position
| is continuously integrated by the controller and stepper is
| driven directly to the correct position based on a fitted
| magnetic encoder and calibration profile.
| IgorPartola wrote:
| You could always run smart steppers like Mechaduinos or the
| similar option from Big Tree Tech. Your firmware might not even
| need to be modified, though there is work being done on Klipper
| to run firmware directly on the steppers so each one is treated
| as an six board responsible for a specific function.
|
| Nothing against your advice just providing another option that
| uses steppers that don't skip an occasional step (that is to
| say that if you ask for more torque from a stepper than it can
| handle, smart or not, it will not produce more torque out of
| thin air).
| jacquesm wrote:
| Yes, that's an option. Technically that is a servo system
| from a classification point of view. Anything that contains a
| motor, a controller and a feedback mechanism is a servo
| system.
| IgorPartola wrote:
| I actually see that as an option (ODrive) in the featured
| article :). I am really curious to play with them myself as
| I'm about to start building the MPCNC.
| yudlejoza wrote:
| General question regarding robotics/motors:
|
| Is there a classification of a system in terms of 'highly
| precise pre-defined/pre-programmed' movement vs 'feedback based
| movement'?
|
| As an outsider, mainly watching youtube demos/videos, I've
| noticed the old kind of robotics, from ABB, Fanuc, and what
| not, with massive robotic arms planted to a firm-foundation, is
| based on precision pre-programmed movement. (I believe) there
| is no feedback though sensors or cameras or anything.
|
| But the new trend is based on feedback, whether traditional
| control-theory feedback, or neural network based reinforcement-
| learning feedback, which I guess eases the rigors of pre-
| program design and makes the system more flexible in new
| situations. But of course it's an open research topic, and
| involves every-increasing sophistication of sensors, high-def
| cameras, lidars, and what not.
|
| Wondering how the choice of stepper/servo, or some other
| mechanisms like hydraulics/pneumatics relates to the above
| categorization.
|
| Thanks in advance.
| jacquesm wrote:
| The feedback is done with optical sensors called 'encoders'
| on the servo axle.
| LeifCarrotson wrote:
| Classic industrial robotics and CNCs have and have always had
| sensors - encoders for position, plus the servo amplifiers
| give feedback for the amount of current the motor is using,
| which is proportional to torque. You can definitely use
| feedback from those control systems. This has been true since
| the earliest systems in the 70s, and is only starting to
| become optional with recent hobbyist 3D printers and stepper-
| based robotic arms and such.
|
| They can also use machine vision in a limited sense. For
| example, I worked with one last week that drove screws. There
| are known numbers and locations where screw pilot holes are
| expected to be, but they have a variability greater than the
| radius of the screw. So, the arm moves the camera into
| position so the field of view is a bit larger than the
| tolerance on the pilot hole, takes a photo, locates the
| circular feature of appropriate size, then moves the screw to
| that location.
|
| However, you're right, these robotic systems are doing
| fundamentally different things than Boston Dynamics and self-
| driving cars. They're solving a different problem. The
| difference is less about stepper/servomotor/hydraulics or
| other control systems, and more about the degree of control
| that the users can and want to exert over the robot work
| environment. If it's easy to mandate that there will never be
| an obstruction in front of the screw you're trying to
| install, and the machine must power down the servos if a
| human is inside the fence, and you can demand of the drill
| machine a certain tolerance on the hole location, you can
| have a more reliable, simpler to debug, quicker to build
| robotic cell. If keeping humans out of the equation and the
| environment obstacle-free is impossible (as on a battlefield
| or parking lot), then you have to reach for less reliable,
| more complex control algorithms.
| tlarkworthy wrote:
| open loop/closed loop. (though industrial arms will have
| proprioception too). Note a good fast moving robot arm needs
| position feedback in the 100kHz range, which a lot of sensors
| are nowhere near.
| fest wrote:
| From what I have seen, what some of the research gets wrong
| is focusing too much on actuators and less on the frame
| rigidity/dynamics. Even if it's possible to arrive at
| somewhat okay-ish position performance using vision based
| feedback, the control system can't really cope with dynamic
| issues (imagine an end effector on a thin, long piece of
| wood: even if you can move it around to a certain position
| based on vision feedback, once you change the load on it, the
| piece of wood bends, once you decrease the load it snaps back
| etc).
| yudlejoza wrote:
| Oh yes, this is one of my pet peeves.
|
| I do think taking into account the feedback from the load
| as well as the weight of each section of the arm itself,
| needs to be done. In addition, some aspects of vibration
| control also need to be incorporated. (I guess the right
| word is proprioception, as mentioned in another commentor).
| fest wrote:
| Yeah, it definitely needs to be done- if not for other
| reasons then just to find out exact machine limits and
| have more data for the next design iteration.
| bluGill wrote:
| In theory you can compensate for this by detecting the
| movement/vibration and moving the cutter to compensate. You
| "only" need 100khz sensors, fast processing and super quick
| actuators. You can lower this a bit with lower depth of cut
| and slower feed rates.
|
| Like I said in theory. In practice we don't really have the
| ability to sense that well. While drivers that are that
| quick exist, they are exotic, or have limited range of
| motion.
| throwaway9d0291 wrote:
| I disagree.
|
| I've been running a small CNC for a while now and though I've
| had skipped steps, they've never been the cause of a failure.
| When they've failed, it's been because:
|
| - I stalled the spindle and I'm trying to plow the no-longer-
| rotating endmill straight through my stock (and if steps
| weren't skipped, the tool would break)
|
| - I forgot to turn on the spindle and I'm trying to plow the
| endmill straight through my stock (and if steps weren't
| skipped, the tool would break)
|
| - I've somehow forced the machine to try to push through its
| limits and crashed an axis into the chassis (and if steps
| weren't skipped, the machine would be seriously damaged)
|
| Basically, the only time the steppers have failed is when not
| doing so would lead to much greater damage, so I'd go so far as
| to say that skipping steps are a feature, not a bug.
|
| If your steppers are failing in the middle of a job where
| nothing has gone wrong, either your steppers or your drivers
| are messed up but it's not because steppers are inherently bad.
|
| I'd recommend servos for applications that are demanding on
| torque, power, speed and/or accuracy. I wouldn't recommend them
| for your first DIY machine because of the additional risk,
| expense and complexity they add.
| beervirus wrote:
| I've always wondered why more home CNC machines don't just use
| closed-loop control.
| analog31 wrote:
| At one time, it was harder and more expensive. You could do
| open loop stepper control with four big transistors, some
| logic, and a whopping heat sink. Closed loop meant learning
| how to tune the loop, and also involved the cost of the
| encoders.
|
| If you're using surplus parts, then getting enough
| documentation to make a servo system work can be touch and
| go. Steppers are pretty much brain dead simple.
|
| Even with servos, the entire machine has to be pretty stout
| in order to ride through a bump that would cause a large
| stepping motor to miss a step. At that point, if it's a
| homemade machine, something else will end up out of kilter
| too, such as your clamping or the workpiece itself.
| sschueller wrote:
| Closed loop stepper controllers have become "dirt" cheap:
| https://www.aliexpress.com/item/4000684515100.html
| ashtonkem wrote:
| IIRC, Servos also can provide feedback, which also helps with
| precision and reliability.
| dbcurtis wrote:
| Steppers skip steps if you are asking for more torque than they
| can deliver. No other reason. It might be: 1) too small of a
| stepper motor, so it can not deliver sufficient torque for
| maximum load, 2) too small of a driver that can not deliver the
| current needed for the motor to reach its rated torque, 3)
| software bug that tries to accelerate the motor faster than it
| is capable of under the load at hand, 4) software bug that
| throttles the driver.
|
| They all boil down to commanded torque greater that the system
| is capable of delivering. Fix your design. Be suspicious of
| software trying to accelerate too aggressively under load.
|
| I have cut a lot of metal on a Tormach PCNC 1100 Series 3
| machine, with steppers. NEVER had an issue. Correctly designed
| stepper systems DO NOT miss steps.
|
| That said, servos systems typically are capable of greater
| accelerations for a motor of a give volume and current load,
| because of the closed-loop control. Use servos for speed, not
| because you are afraid of skipped steps from a stepper.
| jacquesm wrote:
| Correctly designed stepper based systems use encoders or
| other feedback mechanisms to detect missed steps and correct
| for them. Open loop systems will _always_ miss steps, and
| most hobbyist aimed gear is open loop because it is super
| cheap.
|
| FWIW I designed and built CNC equipment for a living.
|
| As for the Tormach machines, they use 3 phase, not 2 phase
| steppers, and use current sensing on the stepper outputs to
| give them a feedback mechanism, and an encoder to close the
| loop completely these drivers and stepper motors are better
| than the ordinary two phase kind that you find in regular
| hobbyist aimed gear.
|
| https://www.damencnc.com/en/nema-34-closed-loop-stepper-
| syst...
|
| They are properly classed as a hybrid servo system rather
| than just a stepper on account of that feedback mechanism.
| Damogran6 wrote:
| You're not wrong, and when the part being cut is worth 5
| figures for the raw stock, it's probably a criticality, but
| it's important to not gatekeep this process, lest it become
| a no-true-scotsman kind of thing.
|
| I built a couple of 3d printers from scratch BECAUSE the
| various components were cheap and approachable. Haven't
| done CNC because my interests haven't taken me there...but
| the thing about advancement is: While one fella is saying
| 'You can't do it that way!' someone comes around and does
| it that way, and the first person is left in the dust.
|
| You can't really stop Laser printers from dropping to many
| thousands of dollars to $70...all you can do is ride the
| wave.
| jacquesm wrote:
| The probability of any given step being missed is
| proportional to the amount of value lost of the step is
| missed. Pretty weird how that works ;)
| Kirby64 wrote:
| That's not necessarily true, it all depends on what your
| desired outcome is. Stepper systems can be open loop as
| long as you're aware of what the torque threshold is and
| make sure you don't exceed that. Obviously a crash would
| exceed that, but there's ways to detect that (e.g.,
| stallguard on Trinamics stuff) without adding an encoder.
| The whole point of open-loop stepper systems is that you
| make sure you stay under the torque limit by a margin (say,
| 30% or so) and you are fine. A properly designed system
| should never lose steps ever, besides in a crash event. Or
| if you load it up with too much side force, but you can get
| that on any machine.
| PragmaticPulp wrote:
| Servos and closed loop systems are almost mandatory on
| large commercial mills due to the sheer scale and mass
| involved, but they're not as mandatory on the hobby level.
|
| In practice, hobby level machines don't have near enough
| rigidity or spindle power to warrant high movement forces
| in the first place.
|
| Nearly all of the hobby CNC machines on the market use
| open-loop steppers. They're definitely not losing steps
| during normal operation.
|
| The topic of steppers vs servos has been covered over and
| over on every hobby CNC forum for the past two decades.
| Closed loop systems are great if someone has extra budget
| to spare, but they're unnecessary for machines using hobby-
| level spindle power.
| nielsole wrote:
| My guess is that the tormach detects skipped steps in the
| controller ("sensorless stall detection")
|
| So it probably does skip steps, but corrects for it
| aidenn0 wrote:
| If you detect missed steps, and apply feedback, isn't that
| now a servo mechanism?
| jacquesm wrote:
| That is exactly what it does. This is also a setup that
| will work fine, but it is actually much closer to how a
| servo would operate and negates quite a bit of the cost
| difference due to the far more expensive drivers, with
| encoders and current sensing on the stepper wires.
|
| The encoders will tell you when to increase power because
| you're about to miss a step, the expected movement is
| lagging compared to the amount of input current. The
| current sensing will help you to detect tool strike
| situations before damage is done to the motors due to
| overcurrent.
| rmu09 wrote:
| Stepper motors also have resonances that you can excite with
| typical step pulse trains, that can also lead to missed steps
| while technically not overstepping the torque budget.
| jacquesm wrote:
| You can work around those resonance points quite well if
| you know what you are doing, the trick is to realize that
| the back-EMF around those resonance points can be so high
| that your stepper is momentarily generating power rather
| than consuming it. If you try to force it through that
| point by adding more current then the stepper will stall
| completely. A properly designed driver that is matched to
| the load of the stepper will use a complex voltage/current
| model that will drive the stepper just right to avoid this
| problem.
|
| This technology originated with the Berger-Lahr company in
| concert with an Italian driver manufacturer for five phase
| stepper motors, which were the first to be driven past this
| resonance point, the tech was then perfected and adapted to
| other, cheaper steppers as well.
| YZF wrote:
| You just need enough margin with steppers so you don't lose
| steps. Particularly during accelerations. That margin shouldn't
| need to be x10. It also depends on what screws you're using and
| whether there's any other reduction. You can get huge linear
| forces from a relatively tiny stepper. You're also going to
| need margins with a closed loop DC brushless/servo system
| otherwise while you won't lose your position you will get a
| position error.
|
| There's also systems with steppers and encoders.
|
| A common issue though is that the steppers are driven at too
| low of a voltage. You also want the right kind of driver that
| PWMs a high enough voltage to maintain the current at speed.
| That's because as the speed goes up the motor has higher back-
| EMF voltage that the driver needs to overcome. Constant voltage
| drive really suffers as the motor speeds up.
|
| But sure, DC brushless + servos are nice, more expensive, and
| require more expensive controllers.
| PragmaticPulp wrote:
| Agreed. High powered servos and associated controllers are
| great with an infinite budget, but properly sized steppers
| are perfectly fine for hobby CNC machines.
|
| The forces involved can be estimated ahead of time with
| simple math. It's easy to verify stepper motor holding torque
| with a common kitchen scale. Cutting forces can be estimated
| with readily-available calculators online.
| imtringued wrote:
| What's wrong with a kit like this? https://www.omc-
| stepperonline.com/closed-loop-stepper-kit/ye...
| jacquesm wrote:
| Nothing, technically that's a servo system using a
| stepper motor as the actuator, which is fine.
| PragmaticPulp wrote:
| Those are great if they're in your overall budget.
| Depending on machine layout you could need 4 of those.
| Spending $400 on motors alone puts this firmly in the
| very expensive end of the hobby CNC spectrum.
|
| The closed loop functionality will never come into play
| with properly sized motors, though.
|
| If the machine gets to the point where the closed loop
| function is trying to make up for lost steps, it's almost
| certainly because something has gone wrong (crashed
| machine into workpiece, for example). At that point, it's
| actually better to halt the machine and alert the
| operator, which is what a lot of people end up using
| closed loop stepper feedback for.
|
| New Trinamic stepper drivers have some built in
| functionality to detect stalled steppers, which can be
| used for the same effect.
|
| Closed loop steppers definitely aren't bad, but they're
| not a must-have for hobby machines.
| archi42 wrote:
| Does this also hold when using drivers like the ones built by
| Trinamic? A servo is essentially a feedback control loop,
| ensuring your motor will slow down if is reaching its torque
| limit. As I understood the data sheet for the Trinamic
| controllers, they can measure various parameters (e.g. back
| EMF, applied current,...). Cooperating with the motion
| controller, a similar feedback loop can be implemented.
| (Thinking about this, a servo would need to "talk" to the
| motion controller as well anyway - if the motion is lagging
| behind due to a torque limit, the motion controller needs to
| compensate for that instead of just scheduling motion on an
| independent axis).
| jacquesm wrote:
| Those should work fine.
| IIIIIKIROY wrote:
| This is my Beast:
|
| https://h2919553.stratoserver.net/images/cnc1.jpg
|
| https://h2919553.stratoserver.net/images/cnc2.jpg
|
| https://h2919553.stratoserver.net/images/cnc3.jpg
|
| Spindel: GDZ-100-3.0 3kw
|
| Inverter VFD: HY03D023B
|
| Motors: NEMA 34 HS5435C-o2b2
|
| MotorDrivers: db860a
|
| Controller: Mach3 USB Controller
|
| Wiring and Components
|
| https://h2919553.stratoserver.net/images/01_Schaltplan.jpg
|
| if you have some questions, e-mail me:
|
| yuriy@mailbox.org
|
| List of Components:
|
| Mechanic:
|
| HGR20 Platz linearfuhrungsschiene 6 set HGR20 - 400/860/1240mm +
| SFU1605 - 350/800/1120/1120mm kugelumlaufspindel + BK12 BF12 CNC
| teile
|
| https://de.aliexpress.com/item/4001307299543.html
|
| Servo motors:
|
| Closed Loop Schrittmotor Kit:Nema 34 8,5 N.m schritt motor +
| Fahrer HBS860H
|
| https://de.aliexpress.com/item/4000324577196.html
|
| OR Stepper Motors:
|
| Nema 34 stepper motor 154mm (Dul welle) 1600 unzen-in 5A + CW8060
| 80VDC 6A motor fahrer + 145A 6 achse MACH3 bord
|
| https://de.aliexpress.com/item/723361510.html
|
| Spindle:
|
| 3KW Wasser-Gekuhlt Spindel Motor ER20 CNC & 3kw Inverter VFD 220V
| & 100mm clamp & wasser pumpe & rohre & 1set ER20 collet
|
| https://de.aliexpress.com/item/32880248302.html
|
| OR Spindle with Changer:
|
| 3KW ATC Wasser Gekuhlt Automatische Werkzeug Andern Spindel motor
| BT30 & 3,7 KW VFD Inverter 220V / 380V FUR CNC Router FRASEN
|
| https://de.aliexpress.com/item/32890491304.html
|
| Controller:
|
| MACH3 4-Axis USB CNC Controller Card Smooth Stepper Motion
| Control Board 100KHz https://www.ebay.de/itm/MACH3-4-Axis-USB-
| CNC-Controller-Card...
|
| Silent Compresor: IMPLOTEX 480W Silent 48dB
| https://www.ebay.de/itm/372008731441
| syntaxing wrote:
| I had a CNC, mill, and lathe but the biggest problem is how
| expensive it is to operate it (excluding the machine). You want a
| good end mill? $100. Vacuum plate because why not? $400. You have
| to use some serious cash to machine parts which forced me to
| pretty much use my 3D printer most of the time since it cost me
| $2 rather than $50 to make the part.
| PragmaticPulp wrote:
| I always warn people that they need to budget about 50% above
| and beyond the cost of their CNC machine to actually use it.
|
| End mills, work holding, dust collection, and other accessories
| will quickly add up.
| bluGill wrote:
| I bought a big old mill for $200. Where can I find even one
| cat-50 tool holder and cutter for $100? I have room for such
| a massive machine, most people don't which is why I got it so
| cheap. (or a way to move - the typical fork lift won't budge
| it)
|
| I actually got two for that price, but on closer inspection
| one has a fatal break in the casting and so it is scrap - I
| expect to make $2500 once I get all the valuable parts off of
| it
| snarfy wrote:
| This is a great resource. I've been slowly building one over the
| last couple months and had to learn all of it from various sites.
| It's nice to have this all in one place.
|
| It's a 1000mmx600mm gantry design I made in fusion 360. I've been
| mostly copying a commercial design (omio cnc). It uses 20mm
| aluminum plates, ground rails, and ball screws.
|
| For electronics I'm using a teensy 4.1 based grbl board (grbl-
| teensy-4) with external stepper drivers, 34mm steppers, and a
| 500w brushless spindle. I'd go bigger on the spindle but I'm
| limited by wattage.
|
| The hardest part for me is the hardware. My design is simple
| based around plates with holes in them, but a couple plates
| require threaded holes in the end.
|
| If you are a software guy, drilling a 12mm horizontal hole 30mm
| deep into the edge of a 20mm x 400mm plate is surprisingly
| difficult. It won't fit in my drill press that's for sure.
| konjin wrote:
| >If you are a software guy, drilling a 12mm horizontal hole
| 30mm deep into the edge of a 20mm x 400mm plate is surprisingly
| difficult.
|
| Punch to center the first hole, then a center drill to start,
| then pilot holes at 3mm, 6mm and 12mm, use duck tape on the
| drill bit to keep the depth right.
|
| If you really need the holes to be dead straight use a handheld
| router those are a great thing to have anyway and pretty much
| all of them have 100mm of or so of travel.
|
| If you're drilling into something very hard skip the 3mm.
|
| A good video on how to tap so you break fewer of them:
| https://www.youtube.com/watch?v=33wfSMsUbuc
| dekhn wrote:
| this is one of the main reasons I bought a CNC- to automate
| work that I can do precisely, but am too lazy to complete.
| yetihehe wrote:
| > If you are a software guy, drilling a 12mm horizontal hole
| 30mm deep into the edge of a 20mm x 400mm plate is surprisingly
| difficult. It won't fit in my drill press that's for sure.
|
| Welcome to the wonderful world of jig-making. "Making" jigs has
| about the same amount of "making" like "coding" in programming.
| You have to invent or search for a jig which will make that
| task doable. I suggest clamping lightly two planks to sides of
| your plate, make a thick block with your desired hole, then
| screw that block onto planks so that your hole is centered
| between them. Now you have a guide for drill.
| Stronico wrote:
| I've always wondered if I was the only one on HN interested in
| cnc machines
| justinclift wrote:
| Nah, there are quite a few people into CNC things on HN. :)
| mhh__ wrote:
| HN is small but self-selects to have people who tend to care
| about what they do so anytime I find myself thinking that for
| any topic it usually turns out I'm wrong.
|
| The most niche thing I actually care about is probably Cold War
| espionage, and even if the exact thing I mention doesn't ring
| any bells with any commenters, someone will usually chime in
| with at least familiarity with the people involved.
| hehehaha wrote:
| I would like to see/make a small CNC build with focus on
| accuracy...since not everyone can afford a KERN.
| yetihehe wrote:
| You are probably looking at PocketNc[0]. VERY small, for
| precision work and has 5 axis. Nice for making micro turbines
| for model engines[1].
|
| [0] https://pocketnc.com/
|
| [1] https://www.youtube.com/watch?v=vMY06dzf7UA
| throwaway9d0291 wrote:
| This is a really good starting place but as someone in the middle
| of retrofitting a commercial CNC, it's missing _a lot_ as well.
| My highlights while reading:
|
| - For an Aluminium frame, you could also use solid Aluminium bar
| or plate. Depending on your location, it might be cheaper/easier
| to acquire. One benefit is that plate especially can be purchased
| pre-milled, so you can get it _very_ flat, which is good for
| things like mounting linear rails, which require high-tolerances
| from their mounting surfaces.
|
| - Missing from the "Linear guides" section is the varying
| tolerances and rigidity specifications of the various options.
| Linear rails can have some crazy high ratings for stiffness (e.g.
| page 27 of [0]) and high degrees of parallelism and overall
| precision. Shafts are often unspecified. However a tradeoff here
| is that linear rails also _require_ high tolerances from the
| surfaces they 're mounting, otherwise they're out of spec and can
| wear out quicker. It also misses that rails can be quite
| expensive. I'd also add that though the rails are low-profile, if
| you want more clearance you can always elevate them.
|
| - Missing from the "Linear actuation" section is how much stuff
| and expense goes into a proper ballscrew setup. In addition to
| the ballscrew and nut (which usually have to be purchased pre-
| assembled together), you also need a fixed support to hold the
| motor-end of the screw (this keeps the axial load off the motor),
| a floating support at the opposite end of the screw, some kind of
| mount to hold the stepper motor concentric with the screw and a
| coupler to connect the screw to the motor shaft. Ballscrews can
| also be expensive.
|
| - I'd actually add a whole section for the stepper drivers. 3D
| printing in particular has led to some interesting options that
| can be applicable to smaller DIY CNCs. Trinamic stepper drivers
| for example are able to drive stepper motors silently, even with
| high current.
|
| - I'd add accuracy to the pros of servos. They're typically
| limited by the resolution of the attached encoder, which can be
| obscenely high.
|
| - The controller section is focused on Arduino-based or derived
| controllers which aren't much seen in much of the DIY CNC
| community. The most popular options by far are [1] Mach 3 and
| LinuxCNC/PathPilot. Personally, I really like EdingCNC [2] but it
| seems to see limited success outside the German-speaking parts of
| Europe.
|
| [0]: https://www.hiwin.com/pdf/linear_guideways_1.pdf
|
| [1]: https://www.cnccookbook.com/choose-best-cnc-
| control-2017-cnc...
|
| [2]: https://edingcnc.com/
| voisin wrote:
| Relevant startup: https://sienci.com/
| stevenpetryk wrote:
| This design seems like it'd be sort of easily replicated with a
| 3D printer and some 8020. I wonder if anyone has open sourced a
| clone.
|
| Edit: it is open source, and easily replicated by design!
| https://sienci.com/dmx-longmill/open-source-and-modification...
| dboreham wrote:
| Stretch goal: get it running BGP.
| daitangio wrote:
| Can I humble suggest to explain what is a CNC router in the
| second sentence of byour blog post? I do not know that is :)
| wccrawford wrote:
| Maybe you should Google it instead? Not every post has to
| explain everything. For regular readers, it would get very
| tiresome.
| daitangio wrote:
| Yes, but at least explain what about the post is...sometimes
| a 4-word phrase is enough... Google is not the solution to
| everything
| bencoder wrote:
| Excellent resource, thank you!
|
| I think the date at the top has the wrong year (2020 / 2021)
| unangst wrote:
| Best advice I read before I purchased my CNC: "buy your second
| machine first". Five years in and I'm _still_ growing into my
| 4'x4' CNC (CNCRouterParts /Avid CNC). Love this thing, only thing
| I wish for is more time to use it.
| wccrawford wrote:
| OTOH, I built an MPCNC router that is good enough for all my
| needs, and was also the cheapest solution I could find.
|
| I not only don't want to replace it, but I bought a diode laser
| CNC in addition to it. I could wish that the laser had a larger
| bed or was more powerful, but it really can do the vast
| majority of what I want. I maybe eventually buy a better one,
| but I doubt it.
|
| Going budget on both of these was a good move. It gave me what
| I wanted while not wasting money.
| noveltyaccount wrote:
| "Buy once, cry once."
| Stronico wrote:
| Valid - but building a crappy first machine is a great way to
| learn how to build a better second machine.
| the_cat_kittles wrote:
| corollary: buy nice, or buy twice
| ashtonkem wrote:
| * Depends on how much space you have to spare.
| jkelleyrtp wrote:
| If you're interested in a garage-size router and don't have the
| time to build, I suggest the Omnio X8 - starts at 2k, and all
| tooling an upgrades will probably run to a total of 3k.
|
| Here's some tips and tricks: https://www.chiefdelphi.com/search
| spindle wrote:
| I followed these instructions to the letter, but was unable to
| connect any of my computers to the internet through it.
| jbay808 wrote:
| Interesting to see a reference both to Moxer Technologies and Dan
| Gelbart's prototyping videos in this post. Is the author from
| Vancouver?
| YZF wrote:
| Dan's company, Creo, used to build high precision machinery
| very similar to CNC machines. He used to give some amazing tech
| talks and his videos are similarly amazing.
| jbay808 wrote:
| His new company Rapidia, which makes metal 3D printers, is
| pretty awesome too!
| YZF wrote:
| Just shows how out of the loop I am... Haven't heard of it
| yet...
| mferraro89 wrote:
| haha no I'm not from Vancouver but I do love Canada. Living in
| Northern California.
| kesor wrote:
| I very rarely use browser bookmarks, but after reading every
| letter of this post I just had to bookmark it. Such great writing
| with short and to the point explanations about ALL the things
| related to CNC mills.
|
| Some years ago I actually tried building my own desktop CNC. A
| lot of the warnings and "don't do this" mentioned in the article
| have gone into my design, which is why it never ever worked or
| did anything and is now laying disassembled in a box.
| pupdogg wrote:
| Building my own 5ft x 10ft CNC from start to finish (ie frame
| design/welding to integration of a controller/software) was an
| amazing journey to learning various engineering concepts involved
| in making an industrial grade machine that churns out accurate
| machined parts every time and all the time (my case being
| wood/composite materials and sometimes aluminum). Video of my
| machine here: https://youtu.be/qpLQEtcjPSY. Here's a video of the
| machine pocketing text CNCZone https://youtu.be/NQFKHyqxvJw.
| CNCZone is a great resource forum for DIYers.
| leon_sbt wrote:
| The machine you built is very professional looking! Great job!
| I wish more people did high quality "last mile" integration" on
| their machines. Energy chain and powder coat makes a huge
| difference in perceived quality.
|
| Couple of questions:
|
| 1. Why did you chose to mount the Y axis servos in that
| orientation instead of where the axis of the servo is
| perpendicular to the floor?
|
| 2. Since you welded the frame, how did you manage the mount the
| linear rails square? Shims? Post weld machining the frame via
| bridge gantry?
|
| 3. What was the total cost of this vs buying an OTS machine?
| I'm guessing around $12k.
| pupdogg wrote:
| Thank you!
|
| 1. How the Y-axis Servos are mounted isn't the ideal
| orientation. Some of my initial decisions, ie for linear
| rails, limited my options based of what I was able to
| fabricate in-house. There were a lot of lessons learned and
| if I was to do it all over, I would actually go with mag
| driven linear servos if I can afford them or have the same
| existing Servos mounted in vertical orientation with the gear
| rack facing outwards engaged with the pinion
|
| 2. Good question! One of the biggest challenges of starting
| to make your own machine are the real life unknowns, which
| might yield one answer theoretically, and another in
| practice. Trying to balance between a realistic budget and
| wanting a unicorn setup, I realized that it was out of my
| budget to machine the entire base frame for this machine. So,
| the Y-axis gear rack was basically mounted to base frame
| using self tapped holes, some shims from McMasterCarr and
| very long hours with a Mitutoyo dial riding back and forth.
| Since the gantry was much smaller compared to the base frame,
| I was able to get the X and Z axis machined from a local
| shop. Here's pix of that: https://imgur.com/a/RLEETAm. Due to
| the DIY nature of my project, I was also not able to stress
| relieve the weldments but was still able to achieve 0.001"
| tolerance for my use case materials (with the exception of
| aluminum which is probably around 0.01").
|
| 3. Having made some mistakes along the way and doing this for
| the first time, my actual expense was around $23k over 1.5
| years. However, that also includes a very nice 2x high volume
| Busch 20kW vacuum setup for the vacuum table (which I got for
| a steal deal on eBay). They would normally run $20k/ea but I
| was able to find and fix DOA units with minimal work for
| around $1600 for both.
|
| I hope this helps!
| jacquesm wrote:
| Fantastic work, very nicely put together.
| SV_BubbleTime wrote:
| I have an 8x4 foot machine, and it's a big boy, old software I
| don't like, steppers, i rarely use it... but I know ONE thing for
| sure, I would probably not recommend a wood frame. Our steel
| frame weighs a figurative ton (or metric literal, IDK) and it
| STILL is not stiff enough for large 3D contoured parts with tons
| of little steps.
| earleybird wrote:
| I'm running a 5x10 which physically is 7'x12'6" with Nema 34's.
| No lost steps over the years, aside from crashes. It will snap
| a 1/4" bit without losing a step. It's on a steel frame that is
| 900+ lbs of steel with 3 sheets of 5x10 3/4" mdf and it still
| vibrates every now and then. Machine time to planning/cad work
| is probably 1:10 which is about in line with my development
| work - 10hrs design for each hour of programming.
| utopcell wrote:
| This seems enormous. If you don't mind sharing, what are you
| making with this machine ?
| earleybird wrote:
| Mostly utility stuff around the house. At one point, a
| custom chicken coop. My use case is unlike
| commercial/industrial. It serves as an 'infinite jig', a
| work bench and a platform for experimenting. I can see
| driving it with Klipper. Mach3/gcode is like batch
| mainframe work. Klipper/Python could make for a much more
| interactive experience. eg. vision for work piece alignment
| and then be able to say "give me a 1/2" dado down the back
| with system 32 shelf pins.
| peter_d_sherman wrote:
| Absolutely gorgeous (and information rich!) web pages!
|
| Well done!
|
| Favorited!
| mianos wrote:
| And watch NY CNC and This Old Tony on youtube. Once youtube
| starts recommending more CNC channels on account of watching
| these two you will be addicted. Watching CNC cutting is probably
| _the_ most relaxing way to waste time.
| geokon wrote:
| The grad students in the lab next door have to sit meticulously
| for hours/days with dental drills drilling out samples from
| rocks. I was hoping to be able to automate it with an affordable
| CNC machine (and an attached scanner bed) - but I seem to not be
| able to find any clear information about step sizes. Here it says
| microstepping is bad....
|
| I also don't really need to do any milling, just adjust to the
| right x-y position and punch a tiny hole and collect the dust.
| Milling rocks in any case is a no-no from what I understand.
| Maybe someone could suggest some ideas for my .. unconventional
| requirements :)
|
| The samples are pretty small (maybe 20cm^2 at the most) and I
| don't need to do it fast... And I prolly don't have a huge budget
| imtringued wrote:
| stepcraft has cheap kits (https://shop.stepcraft-
| systems.com/stepcraft-2-300-construct...) and also offers them
| preassembled for a reasonable price.
| jbay808 wrote:
| Microstepping isn't bad. The author says it reduces torque, but
| it does not. That is a myth.
|
| As long as you are below the maximum pulse frequency that your
| controller can process, there's no penalty at all to
| microstepping.
| fest wrote:
| I recall reading some hobbyist experiments that show that not
| all drivers implement microstepping equally: some have very
| bad angular linearity.
|
| I can now find this article, but I think the one I remember
| reading also tested the torque in microstepping vs full step
| mode: https://hackaday.com/2016/08/29/how-accurate-is-
| microsteppin...
| jbay808 wrote:
| Definitely, if your driver is bad there might be no
| _improvement_ from microstepping, either.
| craftinator wrote:
| Bad microstepping timing in either the controller and the
| driver will definitely reduce torque.
| throwaway9d0291 wrote:
| > Microstepping isn't bad. The author says it reduces torque,
| but it does not. That is a myth.
|
| It's more complicated than that [0,1] and characterising it
| as a myth is dismissive and wrong.
|
| [0]: https://www.faulhaber.com/fileadmin/user_upload_global/s
| uppo...
|
| [1]: https://www.njr.com/electronic_device/PDF/application_no
| tes/...
| jbay808 wrote:
| It's not more complicated than that. There is a confusion
| between _incremental_ torque, which does get reduced (as
| correctly noted in the above) but only because the
| _increments_ get reduced, and _stall_ torque or _holding_
| torque, which in almost all cases do not. The latter are
| the ones that people generally care about, but because they
| read about a reduced _incremental_ torque, they get the
| misconception microstepping creates some torque compromise.
|
| But a full-stepping motor _also_ has bad incremental torque
| for small displacements; by disabling microstepping you 're
| just forfeiting the option to command them.
|
| If anything, microstepping lets you run even closer to the
| motor's torque envelope, because you're less likely to
| induce a dynamic stall by either exciting a resonance or
| letting the stator's magnetic field get too far away from
| the rotor angle.
| YZF wrote:
| I tend to disagree with the author there. Microstepping isn't
| "bad". The biggest issue with hobbyist setups is that they have
| problems with the higher step frequencies required. If you have
| a good controller and driver you should probably go for higher
| micro stepping resolution. It will give you smoother motion
| (less vibrations/unintended frequencies) and better positional
| accuracy.
|
| Anyways, for your use case it sounds like that isn't relevant.
| What positional accuracy do you need? What screws are you
| planning to use? Start there. Most likely a full or half step
| setup is more than enough for your purposes and just make sure
| you set the motion parameters right... The cheapest solution
| for X/Y positioning is going to be something like fixed voltage
| (just using some transistors to switch the stepper motor
| phases) and stepping via software at slow speeds.
|
| What's your budget? What's your more precise requirements?
| (working area, accuracy, speed etc.?) What can you build
| yourself vs. buy? Depending on what you need and what you're
| comfortable building it's either a trip to your local hardware
| store or just buy a cheap off-the-shelf 3-axis CNC kit.
| KaiserPro wrote:
| I would personally save your self a bunch of effort and get a
| openbuilds/ooznest workbee.
|
| Its a kit, should be ~$1700 all in. Its repeatability is rather
| good (0.05mm something like that) the firmware and software are
| all tuned for that machine (assuming you use a kit)
|
| sure you can just do it all yourself, but if you've never done
| it before its going to cost months of your time
| windexh8er wrote:
| Growing up my dad was a machinist. This was in the 80s and CNC
| was what he evolved into from manual die cutting. He did a lot of
| government work where they most often times didn't know what the
| part was for or it was only a subset of the components. Most
| often times he'd be working on a 10+ ton die for a huge part,
| think landing gear, where the tolerances were in the thousandths.
| I always thought that was amazing the precision he could achieve
| by hand. That became even more remarkable to me as I got older
| and realized machines were now doing the math. About 4 years ago
| I built a homelab CNC. I wanted something more robust than a lot
| of the belt driven options out there and settled on a company
| called CNCRouterParts (now called AvidCNC) [0]. The downside is
| it consumes a fair bit of space. But between the laser cutter
| (Glowforge), 3D printer (Prusa) and CNC (CNCRouterParts) you can
| do quite a bit of light fabrication at home these days.
|
| [0] https://www.avidcnc.com/
| jacquesm wrote:
| Large or precise, pick one :)
|
| Making large, precise workpieces is an artform, you have to
| take temperature of the workpiece into account, compensate for
| that, expansion of the bed and so on. Very tricky to do that
| repeatedly with any degree of accuracy.
| xupybd wrote:
| I work with commercial CNC machines. I think people are missing
| out on the second hand commercial market. One of our most
| reliable CNCs is an old pod and rail that cost $10k. It is much
| more than any hobby machine.
|
| Please if you're getting into this look around at second hand
| machines. You'll be able to do really well if you want to setup
| an old 90s machine with new electronics. It's not as complex as
| building one from scratch and you get much better mechanical
| components.
| freeqaz wrote:
| How much would these machines have cost when they were new?
| Just trying to get an understanding of the price break vs the
| "risk" with older equipment. Time goes on and I imagine the
| motors + other mechanical components improve.
|
| But maybe that's a bad assumption from working in tech for too
| long?
| xupybd wrote:
| They do wear out. But some of the things will last and last.
| The square frame will last forever unless it gets a really
| big impact. This is important because holding square is the
| only way you are going to get accuracy. I have no idea how
| people do this with a self assembled frame.
|
| The main spindle might have issues with bearings but you
| should get a lot of life out of one. Ours run 16 hours a day
| and last 10 years plus. As a hobbyist even if you buy one
| with 95% of its spindle life left you are not likely to wear
| it out.
|
| Keep the machine greased and it will last. A good machine
| will come with a service manual and tell you how often to
| grease each part. Most will have an auto greaser that will do
| most for you. Just have to keep it topped up.
|
| All parts are easily replaced. Except the electronics and the
| computer but if you are wanting to build your own you're
| replacing them anyway so it's not an issue.
|
| Vacuum pumps need regular servicing and replacement Blades
| every now and again but again hobbyist use they will last a
| long time just keep the filters clean. They are almost always
| 3 phase so that might be an issue.
|
| They have AC servo controllers that you would have to
| interface with and normally have a can bus for all the
| peripherals I don't think it would be too much to get all of
| that going.
| freeqaz wrote:
| Thank you for the details! That's super neat to know about.
| Going to keep this in the back of my mind for the future. I
| just moved into a place with a garage :)
|
| I'll have to search for a way to run 3 phase power out of
| residential. Not sure if that's even possible. I'm curious
| though!
| bluGill wrote:
| Most new industrial 3 phase equipment is running from a
| VFD which gives speed control. 20 years ago 3 phase was
| used because the power company would supply you 3 phase,
| and otherwise single phase was used. Today many home
| washing machines have 3 phase motors, since a VFD is
| cheap and 3 phase motors have some nice features.
| jacquesm wrote:
| And you can now get cheap single-phase to three phase
| inverters to drive that gear. You won't be running it at
| full power but a 240V socket will happily drive such an
| inverter/motor combo at rates that most hobbyists would
| be more than happy with.
| bluGill wrote:
| Single phase to 3 phase inverters are just a different
| name for VFD. Running a 3 phase VFD on single phase
| (tieing all 3 phases together) works if you derate the
| VFD/inverter. An inverter designed for this application
| should already be rated correctly.
|
| There is no derating the motor when running on a 3 phase
| VFD/inverter if you have the correct specs for
| everything. If you are trying to run a bigger motor than
| any link in the chain it might work so long as you don't
| try to draw more power from the motor than the weakest
| link in the chain.
|
| There is a static phase converter which does derate the
| motor. They are the cheapest way to run 3 phase from
| single phase, but otherwise don't have much to recommend
| them. They are NOT inverters.
| jacquesm wrote:
| > Running a 3 phase VFD on single phase (tieing all 3
| phases together) works if you derate the VFD/inverter.
|
| Interesting, I've never tried that.
|
| Yes, those cap-and-coil based 3 phase 'convertors' are
| more of a fake 3 phase than the real thing and they will
| put a lot of stress on one of the three phase windings of
| the motor and hardly any on the other two.
| jpitz wrote:
| There are rotary converters and variable frequency drives
| - the latter are more flexible.
| xupybd wrote:
| Oops just realised I didn't answer the price question.
| It's hard to give a price. Our pod and rail would have
| been $300k +- 50k new. A top end in that range could be
| up around $750k. The low end maybe $150k.
|
| The type I work with are for wood working. Manufacturing
| cabinets and furniture. So very big (6m long work
| surface) but not capable of metal work. But there is a
| huge range out there.
| yeuxardents wrote:
| Where does one look to search for second hand CNCs?
| LeifCarrotson wrote:
| You can look for second-hand components and machines at
| surplus industrial suppliers and auction houses. When an old
| product is deprecated, it's often cheaper for a big
| manufacturer to get rid of the equipment and buy new for the
| new product line, find out where obsolete equipment is going.
| It's not worth paying $100/hr for an integrator to repurpose
| with no warranty, but at hobbyist $100/week budgets that
| scrapyard is full of treasure. Some manufacturers and
| integrators will have "boneyards" of old equipment that
| they'll purge on occasion.
|
| The article said that Teknik Clearpath servos are considered
| a great value, and they are, but even their smallest
| fractional HP 24V motors cost more than some name brand Allen
| Bradley (unofficial slogan "you can get better but you can't
| pay more!") 3-phase servos at my local supplier:
| https://www.surplusindustrialsupply.com/motors-mot.html
|
| These places are like a garage sale for industrial lego.
| mtreis86 wrote:
| https://bidspotter.com
| xupybd wrote:
| https://www.ebay.com/itm/Biesse-Rover-18-CNC-
| Router/25435957...
|
| They are on most auction sites but your best deals are going
| to be liquidation auctions. There will be auction houses that
| specialise in these in your part of the world.
| oflannabhra wrote:
| Do you have a recommended process for accessing the second hand
| commercial market?
| HeyLaughingBoy wrote:
| Auctions. There are any number of online auctioneers selling
| off machine shop tooling (going out of business, upgrading
| and getting rid of old stuff, etc.).
|
| I haven't bought CNC machinery that way, but I've gotten
| tooling, measuring equipment, etc. for pennies on the dollar
| buying from auctions.
|
| And like jacquesm said, EBay.
| jacquesm wrote:
| Ebay, and specialized traders. Also: contact the sales people
| of new machinery for early access to trade-ins.
| Azrael3000 wrote:
| I just started building a MPCNC, so I still have time to change
| one thing or the other, so I'll give your post a good read.
| Thanks for taking the time to write everything up.
|
| In the German community Estlcam [0] seems to be used a lot. With
| a 50EUR price tag it seems quite reasonable and it might be a
| nice piece of software to try out.
|
| [0] https://www.estlcam.de/
| the_cat_kittles wrote:
| if you find cnc routers cool, as i once did, i recommend you
| check out the world of machine tools- i.e. things that are used
| to make steel (and aluminum) parts. i would suggest starting by
| understanding how a manual lathe and vertical mill work
| (blondiehacks on youtube might be a good place if you are totally
| unfamiliar), and then seeing how they are driven with cnc is very
| cool. though that part is somewhat similar to cnc routers, but
| just much more demanding. and the precision is _incredible_ if
| you arent familiar with the world of machining- even low grade
| hobby machines can hold tolerances of 1 thousandth of an inch
| easily across 18 " of travel. its also a very interesting world
| because its been steadily evolving over the last 100 years, and
| metalworking for who knows how long before that. just be prepared
| to watch 1000's of hours of youtube videos, machinists like to
| make 45 minute+ videos for some reason.
| Animats wrote:
| I miss TechShop. A Tormach 3-axis mill and Shopbots in several
| sizes. I don't have enough need to have my own shop, but I was
| happy to pay TechShop to use their variety of machines.
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