Thread dial gear

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Hukshawn

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Anyone remember ages ago I first came here because my lathe wasn't cutting threads right, and we discovered some gears were mismatched and my thread dial gear was wrong?
I finally have the ability to make gears, I'd like to make one for the dial. Forward and reversing the lathe to thread works, but it's very difficult when you have to thread to a shoulder or internally. I've chewed up many parts because the lathe spun too far.

I've never known the math or what resources guys use to figure out the gearing.
I need to figure out what size and how many teeth to cut.

Can we start this process?
 
I made one for my SB lathe about 40 years ago... Wow, I'm getting old! :) Anyways, if I remember correctly, I counted the number of threads per inch on my lead screw (6) and multiplied that by the numbers I wanted on my dial (4) and ended up making a 24 tooth gear. I made the dial numbered one, two, three and four 90 degrees apart with smaller lines between the numbered ones. Each numbered line represents one inch of travel on the lead screw. So, when the dial goes from lets say 1 to 2 it means 6 threads have passed (or one inch of travel).

So, count your lead screw threads and multiply it by 4 if using/making a four numbered dial, which is typical.

Good luck,
Ted
 
Oh that's quite easy.
How would I determine the size of the gear?
 
Thickness isn't important. I made a worm wheel, not a flat gear. I really don't remember how I came up with the total diameter of the wheel, probably from the Machinery's Handbook. The radius that is perpendicular to the axis of the gear is based on the diameter of the lead screw and pitch. You should be able to find all the info you need in the Handbook or on-line. Look up worm wheel.

You don't really need a worm wheel if you make the gear thin enough. The idea of a worm wheel is that the gears are cut at the same angle as the lead screws thread pitch and it "cups" the lead screw for full contact, although that is not necessary. I know a guy who found a gear with the right teeth and cut it down very thin so its' straight teeth would fit into the helix pitch on the lead screw.

I hope I explained that OK... it's hard sometimes with text.

Ted
 
I already anticipated the helix and cupping the gear. I just need to figure out the diameter. I've been searching online, but coming up with nothing so far
 
There is nice program to determine alot about gears here http://www.wmberg.com/resources/tools
I think that the sprocket download is the right one (maybe) it has been a long time since I downloaded the program---mine says "Berg Gear Specifications Program" on the top of the chart


EDIT: I don't think that is the right download---I can't find it on their website anymore.
 
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Must be you don't have a Machinery's Handbook available, but I would think you could find something on line. Check out the link jocat54 gave.

Bottom line:
For this application you really don't need to be all that precise. Basically, the gear teeth just need to fit into the lead screw without slipping. It's not like you're cutting a precision gear that will run at a certain distance spacing wise and needs exact clearances, engagement, etc. etc.. You'll just swing the threading dial in until the teeth mesh securely and as long as you have the right number of teeth and the dial is marked correctly for the gear you'll be good enough to function.

As a very crude way of doing it that will work is to do this: measure the thickness of one of the threads on your lead screw around half way deep or so in. Double this measurement (for one tooth and one space between the teeth) and multiply this by the number of teeth on your gear. This would be roughly the circumference of your gear. With the circumference you can calculate the diameter. Although very crude (I would only use this if all else fails because it's better to learn how to do it the correct way) this should work.

Good luck,
Ted
 
I went to the website. It offers you a .zip file to open. I don’t own a pc to open a zip file. I use mobile for this site. I’ll see if my (old) Mac book will open it.
I’m sure I could also use the dimension of the old incorrect sprocket that’s in the thread dial now, and just cut it with the correct number of teeth.
 
Google "worm wheel calculator". I just did and got information overload!

Ted
 
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