Hi John,
Yep that does it nicely...

As you know I already have a power feed set-up on my mill and use it quite a bit now that it's there.
If there is a better way of delivering the power then I would certainly consider a change. At the mo I'm yet to be convinced.
My thinking is with a windscreen motor the worm drive gives quite a large gear reduction ratio, so the motor is not turning particularly slow at the lower speeds.
My other finding is that the lower speeds are not really of much benefit in real life and I tend to use it flat out 99% of the time.
Half speed can sometimes give a slightly better finish, but not for everything or every type of tooling/material I have used.
I think too much effort has been put into designing a precisely variable speed (voltage) output on my part. But this of course in in hindsight.
Two speeds, one at 5V and another at 18V would be more than adequate in my opinion. With this in mind I'm thinking an old computer power supply with 12V & 5V outputs would be more than sufficient for those electronically challenged. It's prob the way I would do it now if I had to start over.
A 9/18V transformer and rectifier would also be a very simple, cheap and reliable way to do this too. Don't worry too much about the exact voltages, it really is not that important

Oh, and these motors seem to be quite happy to run at 25V without any signs of distress too....
I hope that helps..

Any chance of the schematic, I've never used a 555 but I know what it is...
