Help Me Fix My Thread Dial

did you mean the ID is .352"? otherwise, thats a TINY gear.

Shawn,

That's correct, the gear is .352" OD. Remember, it came off of a 7x14 mini-lathe. The one-piece gear/shaft is 1.4" long. The dial is .786" diameter. Here's what the shaft and the complete assembly look like. Let me know if you still want it and I'll get in the mail this afternoon.


Tom
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Credits: Images were copied from littlemachineshop.com

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Hmmm, do you think it would still work if I incorporated that gear into my dial? my dial and mount are about 4" in height and the number face is probably 1.25"ish... yours being that small, as is, no way wouldnt fit, but if things are somewhat universal, I'll make that bad boy work. a gear that small meshes with a 3/4ish 8tpi screw?
 
Hmmm, do you think it would still work if I incorporated that gear into my dial? my dial and mount are about 4" in height and the number face is probably 1.25"ish... yours being that small, as is, no way wouldnt fit, but if things are somewhat universal, I'll make that bad boy work. a gear that small meshes with a 3/4ish 8tpi screw?

If Shawn's 14T gear has an O.D. of .600'' as mentioned above, then a 16T gear that is .352'' O.D. will not mesh with his lead screw. It seems that a 16T gear that would work for Shawn would have to have an O.D. of ((16/14)x .600'').
 
I overlooked the gear size in post #1. I really think now that the one I have is probably too small to work with Shawn’s lathe, but I’m sending it to him anyway so he can play with it and maybe get something useful from it. If not, maybe he can pass it on. It’s just taking up prime space on my junk drawer that I need for more valuable junk anyway. ;)

Tom
 
It seems it would be possible to cut a simple gear and tilt the mounting to match the lead screw thread angle.
 
i was looking at my thread dial gear. it almost looks like someone made it. you can see scraping marks on the collar above the gear. why someone did this is anyones guess.
i started to figure out what i needed to make a new one.
i decided on 16t as i dont believe a 32t gear will fit within the dial housing.
the gear that is on there is 14t with a diameter of .600". i find this gear quite small and it jumps a bit when the keyway passes by.

so, if i take tubalcains math, i get a pitch of 26. (no idea if acme thread pitches are different... someone can correct me)
doing more math i determined i need a gear of 1.625" with a pitch of 26 with 16 teeth.

im sure i can find a website or an app that will help design a pie chart layout so i can just make this gear manually on the lathe, really. i was looking at a dividing head, and im still considering it, but, seems a bit much. but who knows when the next time ill actually need/want one and one will be available at a good price.
One thing that regulates the number of teeth is that the numbered lines on the dial indicate 1" distance traveled by the carriage; this universal in lathe design. The pitch of the gear will be determined by the threads per inch on the leadscrew, the diameter will be determined by the pitch diameter of the number of teeth plus twice the adedendum of the circular pitch of the gear. A worm gear meshing with an acme screw would be circular pitch, not diametral pitch.
 
As mentioned, the gear needs to be wide enough to bridge the keyway. On my Hercus (SB9A clone), it is about half an inch thick. When I made a threading dial for my Storebro lathe, I used ABS for the gear. Works great, but no keyway.

In this case, however, I would be cautious about using any plastic for the gear. As the keyway rotates past he gear teeth, it could act as a cutter and take a little bite of plastic with each pass. Not much, but over time, the teeth would get thinner. Better to use brass or mild steel.
 
If the machine has a keyway incorporated into the lead screw build an enveloping gear for the dial, I owned a Clausing lathe made in the 50's/60's that was made just this way. The enveloping gear shape will easily span the keyway without interruption.

Like this.
threaddialgear_zpshsukg1at.jpg
 
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