I’m trying to design a ratchet and pawl to fit in a compact space ~40mm diameter and handle +200 ft-lbs or torque. Can anyone point me to some good references?
I know my 1/2" torque wrench with ratchet head goes above 150 ft-lb. There's probably some safety factor there. Life requirements were not stated. OP gave an envelope dimension that's a bit larger than the guts of a 1/2" ratchet, and a bit smaller than the typical 3/4" ratchet.
I should have said, copy the geometry, and scale it up to use the space available.
Taking apart a commercial ratchet is fine however, he will need to figure out the alloys involved, heat treatments, surface treatments, etc. This is an expensive process and still he will have no clue regarding safety factors. Any graduate mechanical engineer should be able to calculate the stresses involved. There is an important and crucial relationship in the pawl - ratchet orientation to insure that the ratchet will not slip and with larger the torque the lesser the slippage (till break).
Before I _write_ 'looks about right', I run a few numbers.
Yes, any engineer should be able to calculate the forces and the stresses. Even I can do that.
I suggested copying a successful design so you start with _geometry_ that's about right.
I've seen lots of projects fail, yes including from homebrew ratchet designs, because a designer was too proud to copy, or at least do some intelligent comparative anatomy and reverse engineering.
OR, if you're intending to use a bunch, see if someone like J.H.Williams would be willing to tool up and supply your ratchet assembly as a component.
Mike, thats why i what a reference book. I don't want to reinvent anything and I want to run a few numbers. Buying one from sears only gets me half the way.
I could swear there's an example ratchet in at least one of my textbooks, and something similar in one of the many 'design' reference books that I bought when I was younger.
I don't trust them so much anymore. The examples in textbooks are set up so the numbers come out nice, and rarely consider other than obvious details. The examples in other books are usually optimized to demonstrate the basic principles at hand, but the authors and artists probably never faced commercial realities, and they are primarily authors and artists, not engineers and designers.
That's part of why I usually take broken stuff apart before I toss it, and sometimes take new stuff apart right after I buy it.
Open up a couple of commercial ratchets, and you'll see what I mean; they won't look much like those sdp-si parts.
You can get greater torque capacity by using multiple pawls instead of a single pawl, but the multiple pawls must be capable of equal load sharing under all conditions to be effective. So the assembly and manufacturing of a ratchet with multiple pawls would require much greater precision (and thus cost).
The first link in your post is a copy from Mechanical Linkages and Mechanical Controls by Nicholas P. Chironis 1965 Page 144 "Ratchet Layout Analyzed" by Emery E. Rossner.
