at home worm gear forming

[dertsap]

I've got a project that i need a 25 : 1 worm gear reducer , after some thought about how i can do this simply from home with the stuff that i have , i came to this idea , i inserted bearings into the gear which has a v groove cut , and mounted it in the lathe tool post with a chunk of aluminum , then I put a piece of 1/2-13 into the lathe chuck , i engaged the gear into the threaded rod and applied more pressure every few minutes , so far I'm about 3/4 done and it works great
figured i'd post this for anyone else who has come across this issue of trying to make crap at home


"http://www.youtube.com/watch?v=jPiAJb7Wv4Y"]YouTube - homemade worm gear forming

[mactec54]

Hi dertsap

Yes thats' a great idea,But you could use a 1/2-13 tap & that will cut it away put a centre in the tap to hold it on centre

[dertsap]

ya , that was my first thought and I figured I would use a spiral flute tap but I was concerned that because of the intermittent cut it would shred the gear , Ive got another one to play with so out of curiosity I may try the tap when I go back out

[dertsap]

ok so in the time it took me have a smoke i mounted this and cut it with the spiral flute tap , its off center on the height but it was a test and it worked awsome

[HuFlungDung]

Did it turn out with 25 teeth or 27?

[dertsap]

no it actually turned out to be 46 ,
the two diameters that i started out with were a bit large (scrapped v-groove bearings from another project ) but I wanted to see if it would work out , after putting a bit more thought to it I come to realize that the dia for 25:1 would be a bit too small so the plan has changed to use a 50:1 ratio which will be slower but it'll do , the final part will actually be measured rather than using the blurry eyeball

[HuFlungDung]

The reason I asked is because, as you probably know, the OD of a standard gear (which yours is not, but still....) equals the (Number of teeth +2)/Diametral pitch.

So the threaded rod has no choice but to follow a different track as it evolves its way down from the OD to the minor diameter of the gear. This would mean on a rigid setup, that its going to have to 'drop' a couple of teeth as it wears its way in. But more likely what will happen is that the original track will more or less be followed, and the teeth will turn out narrower than they should, with less than perfect form.

Now I realize you may not need perfect form, but you may want to control the exact tooth number at some point. So you might need to consider what your starting OD should be in order to end up with the right tooth number, or else provide an external method of driving the blank positively at the correct ratio relative to your 'hob'. This applies also to hobbing with a thread tap.

[dertsap]

thanks for the tip
the last time i looked at anything that had to do with gear cutting was over 20 yrs ago , I don't need it to be perfect but I do need the teeth to fall in where they should be so i can definitely see the importance of starting with the correct od in order to get it on the right track

[Zathras]

This has already been done before (sorry) by the amateur astronomer crowd.
For some really good info on hobbing worm gears on a lathe, see here;

http://www.atmsite.org/contrib/JSAPP.../wormgear.html

and also here;

http://www.bedair.org/Worm/Worm.html

[Geof]

As Hu says, sometimes you do need proper synchronization between the cutter and the blank to keep the pitch correct right from the beginning. See post #6 in this thread: Single point gear cutting

[dertsap]

ok , now I totally get it , the pitch on these look pretty good by eye but that is by eye , I'll have to do some more testing and hog out a good chunk of material and see how many teeth i start with and how many I end with and hopefully it's all falling where it should be otherwise I don't have another gear to sync with and I'll be hooped

one thing that I have not been able to find is how to properly calculate the torque created with worm gearing , any ideas?

[Geof]

......one thing that I have not been able to find is how to properly calculate the torque created with worm gearing , any ideas?

With a 50 : 1 reduction one turn of the worm moves the gear 1/50 fo a turn so the torque, if there are no frictional losses is multiplied 50 times.

Friction does exist and just how much of the torque multiplication is lost due to friction can vary very widely. I think it would be surprising if your worm reduction is better than 20% efficient without lubrication and maybe 30% with lubrication. But I could be way off in these guesses.