"steamer" wrote in message
...
I've got a situation where I have to drill 3 holes, then accurately
cut out a slot in the lid of a small cookie tin. I made the fixture pictured
here to do the deed:
http://www.flickr.com/photos/steambo...57624880649814
--The trick I came up with: I layed the thing out with a measuring
tape, making certain that the center of the round thing was a little over
some nice round numbers in X and Y, relative to a reference corner. Once
everything was drilled, tapped and fastened in place I put the fixture in
the vise with a part mounted. Using a dial indicator that touched the outer
rim I found the exact center of the part. I reset my DRO to 0,0 here and
then went looking for the edge of the fixture with an edge finder. I marked
down the numbers, then milled those two edges to 'round out' the distances.
Next time I use the fixture I know the center of the round thing is exactly
6" in X and 2" in Y, instead of some weird number I'd never remember.
--Still and all I'm not real happy with the fixture and I'd be
interested to know what others may have done in similar situations. I didn't
want to go overboard on design since I'm only doing maybe 50 of these and
the 'customer' is me. ;-)

For one-off's I've used plaster of paris to make a holding jig. It's readily
removed with just water. In your case could you spray a part with mold
release and fill it with bondo, or similar, to make the jig?
Art