DoN. Nichols wrote:
In article .com,
wrote:

I have a drill press, and I need to center a hole in the face of a
cylinder. I would be perfectly happy to one hundredth of an inch
accuracy. An X-Y table attached to the drill press stage would do the
job, but I suspect that for the level of accuracy that I need, there is
a simpler solution--and I just don't know it.

I've tried scribing diameters across the face, and picking where they
intersect--but the results have been less than impressive. Does
someone have a trick for this?


What did you use for positioning the diameters? A V centering
head on a combination square should do a pretty good job, as long as
your scribe has a very skinny point, and you angle it so the point is
right along the edge of the scale.

Then, you need a spotting drill and good magnification to get
the hole started as close to the intersection of the lines as possible.
Once that is done, you can move up to a larger bit. But 0.010" may be
pushing it if you don't have experience in doing this.

Better, of course, would be a lathe of sufficient size with a
4-jaw chuck, and a good indicator, and a center drill in the tailstock
chuck once you get the end running true.

Good Luck,
DoN.

Here's a very simple, but surprisingly accurate method.
Place a small pointed rod in the drill chuck, a countersink bit will do
at a pinch as long as it comes to a point. Place the bar in position as
close as you can by eye and lay a flat metal strip horizontally across
it - a 12" steel rule will do nicely. Lower the drill chuck so that the
pointed end of the rod gently pinches the rule between it and the bar.
The chances are that this pushes the rule off the horizontal because the
point is not on the highest part of the bar. Move the bar so as to get
the rule as horizontal as you can get it. Replace the pointed rod with a
slocome and start the hole.

If you do the maths you will find that the rule being off-horizontal by
1/2 degree translates into an accuracy of approx. 0.004 x the diameter
of the bar. Half a degree from horizontal is very easy to spot when you
compare it to other horizontal things around, so this method can easily
give an accuracy better than 2 thou on an inch diam. bar.
I hope this helps.

--

Regards, Gary Wooding
(To reply by email, change feet to foot in my address)