Sawtooth Rack

[ConceptTransporters]

Does anybody know where I can purchase a sawtooth rack for a rack & pawl assembly? It's for reverse travel prevention. The best I can describe the mechanism is that it's the main functioning characteristic of a common jack stand that you put under your car. I need to bolt one between two linear-motion parts to serve as a safety feature and it has to be about 4 feet long. Standard racks have 14 1/2 or 20 degree gear faces. A sawtooth has a zero degree face on one side and some aggressive face angle on the other. I've seen plenty of rotational ratchet/pawl devices for sale in typical supply houses, but the linear version is looking like it has to be a custom make thing. Any help locating one of these for purchase would be greatly appreciated.

Thanks,

Concept

 

[tygerdawg]

It sounds like your tolerances are very fat or even undefined. Fatigue strength doesn't appear to be a strong consideration. It's probably very cheap to make from simple bar stock. Call a gear making shop.

TygerDawg

 

[hydtools]

In machining, keyways are broached in a bore. The broach looks like a saw-toothed rack. Would that work?

Ted

 

[eromlignod]

You'll probably have to design one and have it machined. There are circular ratchets that you can buy off the shelf, but I don't think I've ever seen a linear one.

The inside angle of the teeth is acute, so they can't be machined with an ordinary end mill. If you design them to be greater than 60 deg. (or, ideally, *exactly* equal to 60 deg.) then you can use a dovetail cutter in an angled mill head. The smaller the angle, the finer the pitch of the ratchet for a given depth. If the ratchet is big enough, I guess you could also mill it from the side with a regular cutter, but you would have filletted roots.

Another option is to design it with a rack and pinion and put a circular ratchet on the pinion shaft. You might also consider an overrunning clutch like a sprag or roller clutch, but you would need to design a release mechanism, since you would no longer have access to the pawl.

Don
Kansas City

 

[ConceptTransporters]

I wanted to purchase it because it's needed right away. But instead I'm going to have one laser cut out of 3/8" stock (with filleted roots, 60-degree angles and snubbed noses). It'll take a few days but I'll get exactly what I wanted.

Thanks for the input.

Concept

 

[GregLocock]

Probably too late, and lasercutting sounds like a good solution, but there are plenty of linear one way devices around, using offset fulcrums to provide a self locking action. Some jacks use them.

Cheers

Greg Locock

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