Interesting To Know

Meaningful discussion outside of the potato gun realm. Projects, theories, current events. Non-productive discussion will be locked.
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jrrdw
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Sun Jul 12, 2020 2:28 pm

Enjoy!

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mrfoo
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Mon Jul 13, 2020 3:38 am

Interesting, but if you're talking about "shop sci-sc-sci-science!", you probably should spend the first part of the video talking about how much "power" you're getting from a screw press.

Also, he keeps going on about friction being the killer, but it's clearly not, as shown by his grease test. In normal usage, a bolt / nut engages only on around 3 threads, so it's unsurprising that shortening the nuts did little to improve matters. What's at play is the pitch angle, which he clearly sort of understands as per his bicycle graphics.

Limit conditions on this, assuming equal material strengths in bolts and nuts, and correct clearance machining for the whole, are:

1 - plastic deformation of the press tip. Dependent on surface area being borne upon until we reach bolt diameter.
2 - plastic deformation of the thread form. With equivalent materials and machining, the 3" bolt should withstand at least 3 times what the 1" bolt can.
3 - Materials failure in shear. The 3" bolt should withstand 9 times what the 1" bolt can, and I'd suspect failure would be around the welds on the nut rather than the bolt itself. We tighten 2" bolts with a sledgehammer, and they've generally been out in the weather for 10-15 years, haven't sheared one yet.
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jrrdw
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Mon Jul 13, 2020 2:50 pm

Question now is, What new project is he going to use his experiments findings / results on?
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farcticox1
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Sat Jul 18, 2020 8:14 pm

I would have guessed the larger screw makes more force because of the shallower angle of the threads :shock:

This is a good description I found in the comments 'Seems like the threads being further from the axis of rotation and thus the wrench having less mechanical advantage is a bigger factor than friction.'
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