- Joined
- Jan 14, 2013
- Messages
- 290
try this link for information on making a worm wheel.
https://books.google.com/books?id=aCcDAAAAMBAJ (page 209-210)
https://books.google.com/books?id=aCcDAAAAMBAJ (page 209-210)
It goes back to the question that I asked in post #2I had no idea when I started this thread just what I was getting into.
This is my setup.
View attachment 106740
Without doing any research I just assumed that at 6 threads per inch and wanting 72 threads on the gear I would divide 72 by 6 to get the circumference of the gear. Multiply the circumference by 3.14 to get the diameter of the gear. This is what I got.
View attachment 106743
It looked great with well formed teeth all the same size and evenly spaced. I was patting myself on the back when I decided I had better count the teeth just to make sure there were 72 of them. After numerous counts I found there were only 69 teeth.
What happened to the other three? Do I need to increase the diameter of the blank by three teeth and start over with that?
Finally I decided I should probably check out some of the videos and sites suggested earlier in the thread. Each place I went for information seemed to explain it differently or didn't give a clear cut answer. I came back here and did a search for worm gear on the forum. This thread from January of 2015 (http://www.hobby-machinist.com/threads/worm-gear-diameter.31182/ )was very enlightening and the formulas were mostly understandable. (No where have a found an answer to why you have to add 2 to the number of teeth)
I think Mark Stephen said it best: " I am beginning to suspect the need to sacrifice small furry animals while standing on my head reciting incantations to pull of this bit of black magic. :lmao: There seems to be very little hard math behind it. " I will gash the teeth first.
Inr 729 Richard offered in this same thread a calculator for free. Well let me tell you it is great and thank you Richard very much. The calculator covers many different subjects and I will recommend it to all.
Later
Ray
Well I haven't given up and will be trying again soon
As you cut deeper the pitch diameter decreases. The diametral pitch remains the same (it's determined by your cutter) so the number of teeth has to decrease. Now, your cutter is driving the gear so you are probably starting with 72 teeth. The mystery to me is how you morph from 72 to 69 teeth without having some malformed teeth........Also how did you compensate for the reduction in diameter as the "cutter" went deeper into the work?
Figuring the ratio is fairly easy. For a single start worm, each turn of the worm advances one tooth on the gear. The number of teeth on the gear determines your ratio. With in reasonable limits, the diameter of the worm doesn't figure in. Its kind of like a helical rack and pinon except the rack is wrapped around a shaft. The pitch diameter of the mating gear is determined by the pitch and the number of teeth.
I would think you need to make the worm. It would be cut like a screw thread but with the proper profile.This is kind of like the chicken or egg theory, which came first. Ok...I can see the worm diameter makes no difference. So, do you make a worm gear with the number of teeth needed and then make a worm to match or just pick a TPI and make the gears to match it?