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Ratchet and pawl design 2
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MikeHalloran
Mechanical
Sears.
Go buy a 1/2" ratchet, take it apart, and copy it.
Mike Halloran
Pembroke Pines, FL, USA
Go buy a 1/2" ratchet, take it apart, and copy it.
Mike Halloran
Pembroke Pines, FL, USA
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gearcutter
Industrial
I agree with Mike.
I'd start off by pulling apart the ratchet mechanism of a torque wrench rated at 200 ft-lbs or better.
Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
I'd start off by pulling apart the ratchet mechanism of a torque wrench rated at 200 ft-lbs or better.
Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
MikeHalloran
Mechanical
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.
Mike Halloran
Pembroke Pines, FL, USA
I should have said, copy the geometry, and scale it up to use the space available.
Mike Halloran
Pembroke Pines, FL, USA
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- #7
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).
For pawls see
For ratchets see
For ratchets see
MikeHalloran
Mechanical
Yeah, I do often _think_ 'looks about right'.
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 Halloran
Pembroke Pines, FL, USA
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 Halloran
Pembroke Pines, FL, USA
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MikeHalloran
Mechanical
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.
Mike Halloran
Pembroke Pines, FL, USA
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.
Mike Halloran
Pembroke Pines, FL, USA
Machinery's Handbook gives a brief outline of ratchet design.
Here's some other references:
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).
Here's some other references:
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).
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