Re: ATM Worm Gears

[Andy Saulietis <iss@pvtnetworks.net>]

Herb Watson asks:

>1) Will the tap track the way I think it's supposed to without ruining the
>tap and/or disc?

Self-feeding the tap probably won't work, you have to pre-notch
the teeth using a dividing head or *accurate* protractor so the
tap will follow the notches & finish the gear teeth.

>2) what happens when you get all the way around the disc and the threads
>start to overlap? What if they don't come out in exactly the same place? Is
>this a chance event or is there a formula I need to use?

You have to get the gear blank diameter to be the pitch diameter + depth
of tooth to not overlap or underlap the gear teeth.

>Is there a better way to do this?

Yes, but you need a means of rotating the gear blank synchronized with the
turning of the tap, via a rotary table & rt angle drive for the tap.
Synchronizing the tap/gear does eliminate the teed to pre-noch the teeth.
A gear made this way will only be as accurate as the turning mechanism. which
is why gear hobbing machines are so *expensive*. I make my own HDPE plastic
worm
gears this way, but I found a surplus 5 arc sec rotary table & built my
own hobbing machine. I use a 1/2-10 Acme tap which has a tooth profile 
almost identical to a regular single lead worm. These taps are ~$70-100 each
though.

Tom Krajci (see archives) has cast his own worm gears using JB Weld & a
flexible nylon threaded rod.





Andy Saulietis
ISS Enterprises
39 Silver Fox Trail
Mayhill NM 88339
Voice: 505-687-3067
Fax:   505-687-3021 (call ^ first)
e-mail: iss@pvtnetworks.net