Identifying a thread

[DPittman]

Okay I started with my Machinery's Handbook and sort of got overwhelmed.

I think it is an acme thread with 8tpi.

Any hints on how to identify a thread without high end measuring tools. It seems to me there are acme, square and "unique" threads that can look very similar especially if they are worn.
Ive never cut acme threads before and this looks like a challenge that Id like to attempt.

 

[Arbutus]

Does't look like a true ACME thread form. Trapezoidal threads have flat shoulders, and the tooth root and tip are the same width

In fact i'd almost say its a worm. What is the mating part?

 

[Loosenut]

Could be a badly worn Acme thread?

 

[Susquatch]

My first thought is worm too, but the adjacent shoulder sort of rules that out. So does the lack of worm wear patterns

Next guess is worn acme. But the gnarly look of the metal at the thread roots says otherwise.

So I'm gunna go out on a limb and say that it's a poorly formed acme thread. The thread roots, the rest of the shaft surface, and the break all suggest that the part is cast. The basic threads were likely cast in too. If so, the surface of the threads were probably cut a bit or burnished afterward to achieve a smooth working thread surface.

Like most threads, you can follow standards to achieve compatibility or a machinist can make whatever he wants. This is a perfectly useable thread but it needs a custom matching nut because the thread profile ratios are not standard.

If you can't find an original replacement, I'd make a new one to match the nut. Forget about casting. Just make a better one out of steel.

Can, we see the rest of the machine where that fits?

 

[DPittman]

Can, we see the rest of the machine where that fits?

The part is from a winch of some sort (pretty sure a hand winch) but I don't have it as just the broken part was brought to me to see if I could remake.
The acme threads (or whatever they are) for a gear that threads onto them. The parts do look like cast iron in the picture but they are not. They are steel.

 

[Mcgyver]

Badly worn stub acme?

 

[140mower]

I'm pretty late to the party and don't have much to add, just curious how you made out.
Any idea why the gear is threaded rather than keyed?

 

[DPittman]

I'm pretty late to the party and don't have much to add, just curious how you made out.
Any idea why the gear is threaded rather than keyed?

I bailed. While cutting acme stub threads is a skill I would like to someday learn, I am not there yet and I have too many other irons in the fire at the moment.
I'm not sure of the exact reason for the design but it is from a hand winch and I believe it might have to do with being able to select two different cranking torque/speeds. I was only presented with the broken part and haven't seen the rest.

 

[historicalarms]

a good quality winch of any kind is always worm& a gear, better quality ones are always bronze/brass material....less binding force under power.

 

[FatherWes]

Are the treads intended to move the gear fore and aft along the shaft during operation? Or is the gear secured to the shaft by the thread? (So the gear rotates with the shaft but the gear is not intended to move longitudinally during normal operation?)

 

[DPittman]

Are the treads intended to move the gear fore and aft along the shaft during operation? Or is the gear secured to the shaft by the thread? (So the gear rotates with the shaft but the gear is not intended to move longitudinally during normal operation?)

Not sure, the gear moves along the thread until it hits the end then I assume the torque force is then directed elsewhere?