On Wed, 31 Aug 2011 13:31:00 -0700, "Artemus"
wrote:


"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


You must be thinking of dry wall compound cause plaster of paris is
permanent, been playing with the stuff for the last couple of weeks.
Took awhile to figure out the correct mix again, probably have it
written down somewhere. Plus BTW, water first, drill, then powder!

Wood works for the OP, I milled a perpendicular round hole through
thin walled round tubing once. For those lids, I'd made a jig to have
it centered and clamp it from the top. Like a plywood disk screwed to
a rectangle of plywood that is left bolted to the table then one clamp
to hold it down the work.

I'm getting to the point of being afraid to throw anything away cause
there are so many alternate uses for things. Like yesterday I was
using one of those rubber spatula's for an extended finger to thread
in a bolt that I could only reach with one finger. Might as well toss
that one in here. Yesterday I was cutting up maple slabs and the
cheapy 2X3 table saw stopped while cutting two at a time. The motor is
bolted onto a approx. 2" X 3" steel box. Found the clip broke that
holds onto the brush holder. Tryed to duplicate the clip and gave up
and soldered the wrong wire to right holder. Got it all together and
as I plugged it in I said "What could possibly go wrong?" and it spun
the wrong direction. Took it apart again, plus had to drill out the
housing to punch out the blind bearing, and instead of re-soldering to
the other brush holder I turned the stator 180 degrees. Took about 3-4
hours, but It has lots of life left now.


SW