I have a customer in Italy who purchased a VX 20 vise. He was having trouble finding the correct size drill bits to install the vise. There are no equivalent metric Forstner bits near the 2-1/2″ and 1-3/4″ sizes. We decided that the best approach would be to initially drill the vise parts with a 1-1/8″ Forstner bit and then open the holes up using a plunge router with a template bearing. There is a metric size drill bit very close to the 1-1/8″ diameter Forstner. My customer had an 8mm router bit and a 21 mm template guide bushing so I created a router guide template that will allow him to make the appropriate size holes.
The template (shown with a delrin front bearing and constraint washer for size comparison) is made from high density polyethylene which is rigid, smooth and machines beautifully.
To use the template you would drill a through hole using the 1-1/8″ Forstner bit and then clamp the template to your work with the hole centered on the drilled hole. You would then use a plunge router set to the proper depth to open up the hole.
My thought is that I would offer a template like this for metric and American size router bits and charge a small deposit fee for the template which would be refunded when the template was returned by mail. This would not be feasible outside the U.S. so I could also offer them for sale. The holes in the template would of course be sized for common router bit and template guide bushing sizes.
If you have any thoughts on this I would really like to hear from you.