[HN Gopher] Someone Built an Engine Crane Out of Wood. Let's Do ...
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Someone Built an Engine Crane Out of Wood. Let's Do Math to See If
It's Safe
Author : NaOH
Score : 22 points
Date : 2021-03-28 04:45 UTC (18 hours ago)
(HTM) web link (jalopnik.com)
(TXT) w3m dump (jalopnik.com)
| kumarvvr wrote:
| As an engineer (electrical at that), there is no point in doing
| any math. That thing is dangerous.
|
| Any math to calculate resultant stress is meaningless, because we
| have no data on how uniformly dense the wood is.
|
| Not to mention it looks flimsy to the point of being cartoonish.
| LorenPechtel wrote:
| All the numbers he worked are far within the strength limits,
| the imperfect measurement of wood strength doesn't matter.
|
| What he showed is the crane is plenty strong enough to hold the
| engine--the failure mode is tipping, not strength.
| wmoser wrote:
| Ok, I glanced at the article and as another engineer, yes it
| looks sketchy and probably isn't safe (applying the rule from
| rigging of: if something doesn't look right it probably isn't).
| I felt the need to address the other issues you brought up
| about being impossible to calculate because it's wood. Wood is
| the original composite material and has been used to safety
| build bridges, buildings, ships etc. For the most part your
| calculations won't be as exact as with metal or other
| engineered material but there has been lots of research into
| this. The US Department of Agriculture/ US Forest Service even
| publish a free book about it. [1] The lumber looks like it was
| bought from a home center and so likely has minimum strength
| expectations [6-3 of afore mentioned book].
|
| I just felt the need to dispel this rumor that is quite
| dangerous that I see all the time at work where people use 1/4
| wire rope slings with unrated hardware as part of rigging
| instead of 1/2 inch Manila rope because "That rope doesn't have
| any rating, it's natural". (It does, about 1/2 the wire rope,
| but needs knots or splices to attach it to thing being lifted,
| not the unrated hardware that comes with the wire-rope.) Like
| someone posting further down, I'm more immediately concerned
| that there is no brace to prevent racking or the use of ratchet
| straps as a lifting device.
|
| [1]
| https://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr11...
| js2 wrote:
| The author is just having fun:
|
| > This whole article is a largely pointless exercise in
| figuring out how strong some random dude's wood crane is, even
| though I have no clue what the load case is.
| thiagocsf wrote:
| The imperial units used in the calculations made my brain hurt.
|
| On a positive note, I suspect Americans are a lot more proficient
| with fractions than people who grew up learning metric.
| OnlyOneCannolo wrote:
| Fun article to read. The author started to get into the more
| likely failure modes at the end when time ran out.
|
| Stability is probably the most important. Next is failure of the
| wood near the screws, which affects stability. Wood has its own
| considerations due to the grain. The American Wood Council has a
| fastener calculator which shows a few of the things that matter
| when doing structural design with wood.
|
| http://www.awc.org/calculators/connections/ccstyle.asp
| K2h wrote:
| 4 vertical 2x4. If they put some lateral cross bracing to keep
| from going all rhombus it will work. How many sticks do you think
| are in a wall?
| Gravityloss wrote:
| Good quality wood has very good bending strength for mass. The
| structure just needs some depth, like there is here.
|
| That's what trees evolved for.
| snypher wrote:
| By depth, do you mean cross bracing? Any discussion about
| lumber strength is beside the point, the fasteners will pull
| out as soon as it goes sideways.
| Gravityloss wrote:
| By depth I meant thickness. But thickness sideways doesn't
| help nearly as much as thickness in the vertical direction.
|
| A beam with a bending load like here can crack from the
| bending at the middle for example. The fasteners at the ends
| are not necessarily the limit. It's different for pure
| compression or tension, there the fastener area sees higher
| load.
| mikewarot wrote:
| There are zero triangles in that structure, it'll fold like a
| cardboard box.
| mindslight wrote:
| This. This is the answer.
|
| Compression load on the vertical members? Who cares.
|
| Strain on the long cross member? Wood fails gracefully and
| you'd hear cracking.
|
| Forward-backward stability? Probably okay if those joints are
| screwed really tight and ideally wood glued.
|
| Side-side stability? Good bye!
| rubyn00bie wrote:
| IMHO, the writing style of this article is horrible. It was truly
| a painful chore to read and probably the least satisfying drivel
| I'll read all day.
| greatgib wrote:
| I totally agree! Impossible to read with an ad break every
| paragraph.
|
| In addition, if doing such a long and detailed article, the
| author could have spent a few minutes to draw on computer clean
| version of his schematics. Instead of unreadable pictures of
| hand drawn thing.
| wrycoder wrote:
| The whole point was to get scrolls past all those ads. It was
| a listicle.
| pengaru wrote:
| This is why I will never own a Quattro vehicle.
|
| Every service involving the engine begins with something like:
| Step 1: remove headlights and front bumper Step 2: remove
| myriad heat exchangers Step 3: remove engine
|
| So of course you're looking at an Audi Quattro platform getting
| its engine pulled in a parking space. I wouldn't be surprised one
| bit if this was all happening just to replace an inaccessible
| $100 part.
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(page generated 2021-03-28 23:02 UTC)