Make A Worm Gear

rdean

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Did you know you could make a worm gear if you had the old shaft? Well me either until I saw a post by another member on here a few weeks back (can't find it now) briefly showing how he cut four slots in a threaded shaft and mounted it in the lathe. He then mounted a piece of round stock on the tool post and proceeded to cut the threads into it.
Well I have to try this so I got a piece of 3/8" x 16 threaded rod and cut four 1/8" slots about 3" long 90 degrees apart and mounted it in the lathe with a live center for support. I had a 1/2" thick by 3" round aluminum slug so mounted that on the tool post. I started the lathe and moved the round closer until it started to turn and to my joy it started cutting into the slug. This is what it looks like after 30 min of cutting.

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So if it works that good in aluminum how does it work in nylon and what about a larger size. I had some 5/8" x 6 acme rod and some 9" diameter nylon rounds to try again. I cut off a 8" piece of the threaded rod and cut 4 slots in it but this time I used a 1/2" end mill offset from the center of the shaft 0.250. That way the end mill would just cut to the middle of the threaded rod and hopefully have a more aggressive cut.

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Never too old to learn something new!
Thanks for looking
Ray
 
Ray, an interesting idea. How did you decide on your gear diameter so the teeth would come out right when you made a full circle? Also how did you compensate for the reduction in diameter as the "cutter" went deeper into the work?
 
Being a newbie on lathe work, gear cutting was still fairly far away on my mental learning list, and then you just had to post this.
I have a need for simple inexpensive worm gear reduction sets for slow motion controls of manual telescope mount
positioning, nothing precision though, and then you just had to turn me into a potential worm gear cutting enthusiast.
I really should stay off of this site, my wife is starting to complain that she so seldom sees me, and were both retired!

Chuck the grumpy old guy
 
RJ
I would like to say that after hours of diligent research and measuring using several math equations I decided on the exact diameter and tooth for each gear but that isn't true. The aluminum one was just trued up on the lathe to be round and not even measured. I decided on the diameter of the nylon one because my lathe will only turn 9 1/2" . There is a formula for figuring all this out but since this was just for fun I just started cutting. The nylon gear has 165 identical teeth as far as I can see but the aluminum gear has three teeth that are cut somewhat narrower so if I plan on using that gear I would cut it down and start over.

ch2co
You have to give it a try really fun
Ray
 
I have seen this done many times on You Tube, but I would like to know how to figure the diameter needed to get a specific ratio. Yes you can make gears this way, but how to get the ratio needed for a project is the biggest problem.
It is very clever and looks great, now how do you make it useful.
 
Just looking at this I think it won't be too difficult to get close to a given ratio. If you take the input in threads per inch times the circumference of the gear blank, I think you will get the input to output ratio. Example: 14 tpi x 2 inch dia x 3.14 = 88.96 or 89 rev input for 1 rev output. Pick a given input thread, and ratio, then use algebra to get the necessary diameter, and see if it packages.
 
Just looking at this I think it won't be too difficult to get close to a given ratio. If you take the input in threads per inch times the circumference of the gear blank, I think you will get the input to output ratio. Example: 14 tpi x 2 inch dia x 3.14 = 88.96 or 89 rev input for 1 rev output. Pick a given input thread, and ratio, then use algebra to get the necessary diameter, and see if it packages.
It seems very simple from the little I've read (I've got a worm&wheel I'm thinking to replace on feed mechanism of my new old Marvel bandsaw), it seems that the ratio is 'number of teeth on wheel : number of 'teeth' (threads) on worm. ie: 60 tooth wheel, single thread worm = 60:1. 40 tooth wheel, 4 thread worm = 10:1. As I said, I'm early in looking into this so correct me please if I've misinterpreted what I've read.
The method shown by OP and further discussed is the way I was thinking to do it. The worm I need to replace is single start thread at 6 teeth per inch, simple enough to cut on the lathe and made extra long, used to cut the wheel. The cut edge of the wheel I need to replace is deeply concave. Which really threw me because in all the places I've looked for replacements, I've seen nothing like. But after I thought about it, it would seem the deep profile is a product of the face width of the wheel. Additionally, the number of teeth on the wheel is 65, strange but almost assuredly to make it proprietary. I'm thinking that a 60 tooth wheel will be just fine.
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Stan,
Sent from my iPhone using Tapatalk

Oh yea, haven't a clue about pressure angle and pitch diameters
 
Andre yes a tap would work much better as it is designed to cut. But I had this acme screw and no tap.

Well John got me thinking that I should make a gear with a predefined number of teeth or gear ratio to see how it works out. I cut out a blank today but ran out of time to turn the exact diameter. Maybe Tuesday I will have time to try it out.

Ray
 
Another trick is, to gash shallow grooves using a dividing head on a mill and a woodruf key cutter or dovetail cutter. These grooves are used to "start" the teeth so that they will aid in dividing the blank into the proper number of teeth.

If a mill and dividing head are not available, you can "go for it" as the OP did in his first post. You do run the risk of getting inconsistent teeth or something similar to making a knurl that has a double start....
 
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