Involute Gear Pitch for ACME Thread

I'm trying to figure out which involute gear pitch works with 8 and 10 TPI ACME thread? By "work" I mean for low pressure application similar to a lathe thread dial or other low torque application.
 

Comments

.1 and .125 inch CIRCULAR PITCH gears. NO diametral pitch gears will be correct.

.1 cp gears are pi *1/.1= 31.4159 DP
.125 gears are 25.1327 DP
 
8 TPI ACME pitch = 1/8 = 0.125
10 TPI ACME pitch = 1/10 = 0.100

Circular Pitch = Pi*D/N

For a 32 Diametrical Pitch gear with a pitch diameter of 1" then

CP = Pi/32 = 0.0982"

That should be close enough for 10 TPI ACME?

Nothing works for 8 TPI ACME, at least with inch gears. Metric perhaps? What size gear is used on an 8 TPI lead screw thread dial?
 
You don't get to pick your circular pitch, diametral pitch, AND pitch diameter. Normally, one would select the desired lead (and starts, if applicable) for the worm, the desired gear reduction. The lead for a single start worm will be equal to the circular pitch of the mating gear. For a single start worm with a lead of .1 and a 32:1 reduction, the pitch diameter will be 1.019". For one with a lead of .125", the 32:1 reduction will require a gear with a pitch diameter of 1.273".

Because of the geometry of the worm, the O.D. will depend on the width of engagement of the gear with the worm Minimally. it should be 1.08" and 1.35" for the two cases cited.
 
Your gear will need to be quite narrow to even work at all. Worm wheels (your gear) have teeth that have an angle that matches the angle of the thread helix. You won't have that with a regular spur gear.
 
Your gear will need to be quite narrow to even work at all. Worm wheels (your gear) have teeth that have an angle that matches the angle of the thread helix. You won't have that with a regular spur gear.
Some one on forum posted using a tap as the work and cut a worm gear. Then turned the worm to match the tap. As PMartin noted, the worm gear would ideally have a radius matched to the worm for more tooth contact.

I'll do some searching and see if I can find the thread that had the tap/worm technique. You might be able to find an Acme tap to match your Acme rod.

Bruce
 
Your gear will need to be quite narrow to even work at all. Worm wheels (your gear) have teeth that have an angle that matches the angle of the thread helix. You won't have that with a regular spur gear.
You are right ... and I need to do it right. I have a PM935 mill and Z axis lock is crap. There are two lock screws/handles located on the left ways. Locking them is getting tedious. My initial thought was to replace the handles with small gears that interface with a vertical Acme threaded rod with a handle at the top. One light twist of the rod to rotate each way lock screw (timed of course). Time is money and messing around under the table to tighten lock screws is a poorly conceived shortcut on an otherwise perfectly mediocre machine.

I am open to ideas. The Bridgeports seem to have the Z lock activated by a handle on the front of the knee. Can this be rigged on my machine? If I had access to Bridgeport I could answer that.

I'm not going to let this go. I am really annoyed over this feature and I will fix it, somehow.
 
Here are some older posts with info on making a worm gear.

Bruce

 
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