[Les A W Harris]

Dfennell,

"I'd like to use a 1/10 pitch .500" Acme screw for the worm. I know this isn't a true worm,".

It is a true worm!
The Berg Data is for Fine pitch worms, the P.A. is fixed at 20*, You need Industrial wormgearing, Machinery's Handbook has the equations, P.A.'s range from 14.5*(Acme Thread form) to 30*, So you have to crunch a few numbers & you're ready to do it!

Got more medical appointments, will be back to check on you,
Happy Worming!

Cheers Les H.