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Gear for threading dial

trlvn

trlvn

Ultra Member
Hi:

A couple of us have noted that the gear in the threading dial on the Craftex CX-706 is a crappy fit to the related screw, as shown in the following:

Gear on thread dial IMG_4803.JPG


There are gear design programs out there that ought to be able to draw a better mate and then print a 3D version. Right?? This seems like the perfect application for a 3-D printed gear--virtually zero power being transmitted and low usage.

I know just about nothing about gear design, though. Is this effectively a "worm gear"? The lead screw is 8 threads per inch. The existing gear has 40 teeth and is about 1.323" diameter.

Is there a web page that would walk a newbie like me through the process? Or maybe a kind member can whip something up?

Craig
cc: @6.5 Fan
 
I had the same problem with my CX701 when I bought it. Took a bit to convince BB that there was something wrong, then they sent me a new thread dial that fits.
 
trlvn said:
Hi:

A couple of us have noted that the gear in the threading dial on the Craftex CX-706 is a crappy fit to the related screw, as shown in the following:

View attachment 32796

There are gear design programs out there that ought to be able to draw a better mate and then print a 3D version. Right?? This seems like the perfect application for a 3-D printed gear--virtually zero power being transmitted and low usage.

I know just about nothing about gear design, though. Is this effectively a "worm gear"? The lead screw is 8 threads per inch. The existing gear has 40 teeth and is about 1.323" diameter.

Is there a web page that would walk a newbie like me through the process? Or maybe a kind member can whip something up?

Craig
cc: @6.5 Fan
Click to expand...
Yes I'd say that is not the right profile gear to mate with the lead screw but it would work.
I think a gear like the one that came with my lathe is more correct.
Post in thread 'threading issues on CX 706' https://canadianhobbymetalworkers.com/threads/threading-issues-on-cx-706.7115/post-106108
 
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Larry_C9 said:
I had the same problem with my CX701 when I bought it. Took a bit to convince BB that there was something wrong, then they sent me a new thread dial that fits.
Click to expand...
Could you supply a picture of the replacement?

Thanks,

Craig
 
I should mention that the existing gear in my threading dial is not a simple spur gear. It has a slight helix angle. It does follow the lead screw but it must be only the very tip of the gear tooth that is in contact. A couple of times when I manually moved the carriage back, the threading dial seemed to get shifted and lose contact with the screw. Which would wreak havoc if I was actually cutting threads!

@6.5 Fan Has Busybee responded at all to your email yet? If they are making encouraging noises, I'll piggyback off what you are doing. If they are not helping, I can try piling on to see if they will recognize that it isn't right.

Is there somebody here that has a PM10xx that can verify what Precision Matthews supplies?

Craig
 
trlvn said:
Could you supply a picture of the replacement?

Thanks,

Craig
Click to expand...
I don't have a picture handy right now but could get one. The original thread dial had a 40 tooth gear. The one that fits properly has a 32 tooth gear if that helps Here is a picture of the gear that does not fit, it has 40 teeth. A way too fine.
 

Attachments

  • Thread dial gear.jpg
    Thread dial gear.jpg
    51.2 KB · Views: 9
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What a GREAT team project where sooooo many could benefit.

My lathe does not have this problem but count me in for support and lots of constructive helpful heart-felt criticism...... And yes, I'm being funny, but I'm also deadly serious - I'll help where I can.
 
If a fellow wanted to try to turn a worm gear himself to match your leadscrew better, here is a simple method that may be good enough for such a job.

This is one of the shorter videos and just shows the basic process, there are longer more detailed videos out there if anyone is interested.

 
i have never made a helical gear, but i have done several spur gears in fusion 360 then printed samples of before cutting on the mill, it was very simple

here is a quick video on how to make a helical gear in fusion 360

then it would be a matter of printing, nylon is the commonly recommended material for gears.....but its tricky to get to print, so be prepared, all metal hot end required
 
I never heard back from BB. Perhaps you should let them know of the issue as well, the more noise they get they may look into it. John Conroy posted in my original thread about a 32 tooth gear on the Precision Matthews machine a friend of his has. It works.
 
6.5 Fan said:
I never heard back from BB. Perhaps you should let them know of the issue as well, the more noise they get they may look into it. John Conroy posted in my original thread about a 32 tooth gear on the Precision Matthews machine a friend of his has. It works.
Click to expand...
Never heard back from BB - What a shocker.
Hope you guys get this figured out, Looks easy enough to manf.
 
phaxtris said:
i have never made a helical gear, but i have done several spur gears in fusion 360 then printed samples of before cutting on the mill, it was very simple

here is a quick video on how to make a helical gear in fusion 360

then it would be a matter of printing, nylon is the commonly recommended material for gears.....but its tricky to get to print, so be prepared, all metal hot end required
Click to expand...
Thanks, but I really want a worm gear; not a helical. Ideally I think I want an 'hourglass' worm gear. May also be called a "Hindley worm".

Craig
 
It occurred to me that the apron already includes a worm gear that is driven by the screw:

CX706 Apron parts.jpg


Part #31 is described as a 17T Worm gear. It transmits power to the longitudinal or cross-feeds as selected. I think it probably needs the hourglass shape to bridge the 5 mm keyway in the lead screw.

I suspect that the thread dial needs a gear that has a multiple of 8 teeth (40? 32? 24?) but I haven't really worked through the ratios.

BTW, the ACME threads on the lead screw are not the typical profile of a worm combination. The profile for the thread dial ought to be much like part 31 above. Which just makes the whole thing more and more complicated.

Craig
 
I don't know if this has value here or not. The thread dial gear on my lathe has 24 teeth and my leade screw is 8tpi. If nothing else, it's a data point.

Regarding Craig's discussion above, the only gear engagement for my leade screw is the half nut and the threading dial gear. The half nut is ONLY used for threading.

Feed operations all use a gear that engages a separate unthreaded feed shaft that is keyed to a sliding gear which in turn engages on a rack along the edge of the bed OR the lead screw in the cross slide depending on which one is selected.
 
You still have to figure out what the modulus is don't forget, that's the most difficult part imo
 
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