Doggggboy
Ultra Member
The same on my little 11 by 36 Taiwanese. Leadscrew is 3/4 inch.
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Gear for threading dial
- Thread starter trlvn
- Start date
Ya, sorry about that. Kinda dumb to leave out the leadscrew diameter. Mine is 7/8"
So 7/8 - 8 with a 24 tooth gear on the thread dial that mates very nicely and firmly with the leade screw.
Also just for information: My South Bend has a 10 TPI lead screw (0.1" crest to crest) and the threading dial has 32 teeth. Since it tracks across the lead screw the pitch of the gear is also 0.1" between teeth which would make the outer circumference 3.2". There are 4 numbers on the dial with ticks half way between or 8 spaces.
Now if i disengage the half nut but engage the threading indicator I find that turning the lead screw through a distance of 3.2" turns the dial from line 1 to line 3. Of course with the half nut engaged it stays on line 1.
Now if i disengage the half nut but engage the threading indicator I find that turning the lead screw through a distance of 3.2" turns the dial from line 1 to line 3. Of course with the half nut engaged it stays on line 1.
trlvn
Ultra Member
Some searching has led to two possible options. First, I ran across a guy making a replacement gear for a Southbend lathe:
The key thing is that he 3D printed a gear that is fairly close and then let the lead screw on the lathe do the final shaping on the teeth. IOW, the printed gear had the typical tooth profile for a worm system. He mounted that on the lathe and pressed the new gear into the spinning lead screw. The lead screw has the keyway which acts like a single tooth cutter. Since the profile was 'pretty close' to start with, it only required a minute or so of fettling to end up with a gear that works pretty well.
Incidentally, the guy sells these replacement gears for about USD $20:
www.ebay.com
Craig
The key thing is that he 3D printed a gear that is fairly close and then let the lead screw on the lathe do the final shaping on the teeth. IOW, the printed gear had the typical tooth profile for a worm system. He mounted that on the lathe and pressed the new gear into the spinning lead screw. The lead screw has the keyway which acts like a single tooth cutter. Since the profile was 'pretty close' to start with, it only required a minute or so of fettling to end up with a gear that works pretty well.
Incidentally, the guy sells these replacement gears for about USD $20:
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Craig
I like this. A threading dial carries no load whatsoever. It just sits there and goes for a ride. If one printed a nylon gear, it "might" last forever.
Ive seen some BB Threading dials on the left side of the carriage. I don't like that. This would make it possible to move it to the right side (where it belongs IMHO).
trlvn
Ultra Member
At first, I wasn't really grokking this solution but I think I get it now: use a 8 tpi ACME tap!! The main issue that remains is size. The lead screw is 20mm so a 3/4" tap is too small. A 1" tap is a bit big. I would guess, though, that a 1" 8 tpi tap might work 'well enough'.
But next, like elephant stew, I'm missing that one key ingredient to the recipe!
Does anybody have a suitable tap that they'd loan me to try this out? The plan would be to do a test or two in plastic to check the size of blank necessary and to verify that the threading dial really does what it is supposed to. A final gear could probably be made from brass.Craig
Making a 20mm 8tpi tap would be a fun project
I agree. You go first......
Do you agree, To cut a nylon gear it wouldn't need to be tool steel, an old grade 8 bolt would work. It wouldn't need a lead-in taper to cut a gear and it would only need 1 flute?
Yup, I agree. Doesn't even need to be grade 8. Which is a good thing cuz I think it would be hard to find a grade 8 bolt with a course thread like that.....
My thought was to use a bolt larger than 20mm and turn to size then make a hss threading tool to cut the threads. Then cut the flutes in the mill. The threads are likely metric buttress not acme so grinding a custom tool would be necessary
Edit-sorry not buttress but some metric acme like thread
Edit-sorry not buttress but some metric acme like thread
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Mine is 22mm 8tpi but not a 60 degree thread. Could be 29 degree like acme but I don't have acme thread gages
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Ahhhh. GREAT IDEA! I Like that WAY BETTER than just machining an existing bolt. And yes, you could use a hardeneable steel but why bother. Any kind of steel will cut nylon. I also totally agree with grinding a tool to make it an acme thread.
Are ANY leade screws 60 degree? I would think they would all be acme or similar.
Acme is 29 degree and Metric trapezoidal thread is 30 degree but looks like acme but of course acme does not have metric sizes so I don't know what to call it.
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The gear on my threading dial is not a straight spur gear like I thought. It Is 32 teeth and the teeth have a slight angle to match the leadscrew
Yes. Mine also has a slight incline rather than square on.
For the CNC Router I used ACME threaded rod for the Z and made a tap for the nylon nut block. However it ended up being undersize and not working well. So instead I made my own.
For the CNC Router I used ACME threaded rod for the Z and made a tap for the nylon nut block. However it ended up being undersize and not working well. So instead I made my own.
Found the taps. The ACME allthread worked but not as well as the custom one. But I think for a threading indicator cut with the tap in the lathe and cutting the thread like a worm gear tilted slightly should work.
Here's also a photo of the two plastic pieces with screws to separate them for backlash. Really should replace this with ball screws like the rest.
Here's also a photo of the two plastic pieces with screws to separate them for backlash. Really should replace this with ball screws like the rest.
Attachments
What size is the acme tap?
Metritoxicated Acme.
I started with the 1/2" ACME all thread. OD is 0.497" for the 10 TPI stuff. The one I made has an OD of 0.506" and in the plastic just cut that little bit deeper and smoother as the rolled ACME all thread has a ridge in the middle of the crest of the tooth.
It's not that hard to cut an ACME thread but the tool tip width has to be customized for the pitch. I used my 5C Collet Indexer to rotate the threaded part and a ball mill to cut the slot. IIRC. Not sure. Many years ago.