Re: [CAD_CAM_EDM_DRO] Cool Worm Gear

Good point there about the gear ratio. Those photos and the description at
that web site Brian posted were a great help. I'm going to give this a
try...might even make a custom tap for the project.

I note how the blank is fed into the tap until you get the desired results.
This could mean two gears with the same number of teeth could wind up with
different pitch diameters when your done...sort of like having a standard
size P.D. and one with a bastard P.D. like we used to have to have for some
of our multi-spindle drill heads. Due to this, I'd strongly recommend
measuring the center to center distance between the cutter and the finished
gear. That way when you build your mounts for these parts you could get the
centers spaced accurately for minuimum backlash.

>Hi Smoke,
>
>With the tap method its quite simple - make some sort of fitting to go in
>place of the tool holder which will allow you to put the blank on a

vertical

>axle, freely rotating and at centre height (in my case with the Harrison
>lathe that involves removing the tool holder and putting a stack of packing
>washers on the bolt which normally holds the toolholder down. Now with the
>blank free to rotate in a horizontal plane, put the tap you want to use in
>the chuck or collet, set it going and wind the blank into it (in the 'Y'
>crossfeed direction). Let the tap
>cut its own teeth and, as it does so it will rotate the blank

automatically.

>Just keep feeding the blank into the tap a bit at a time until the teeth

are

>cut to full depth (whatever you want that to be). I normally cut them to
>almost the full depth of the tap teeth then just tidy the top edge up with

a

>bit of emery paper and cut a chamfer on each side to make it look pretty.
>That's it at its simplest. As another correspondent said, it can be useful
>to have first gashed the blank with the right number of teeth but it isn't
>really necessary if you have the size of the blank about right. This method
>can be quite useful if you want to make a worm and wheel with an unusual
>ratio - one that I needed was 127:1 - not a particularly easy number to
>divide.
>
>Ian
>--