Using a 1/8" wheel, the pilot hole was the controling factor. As they
were already in, we could do those with a 5/32" pilot hole without
problems, but have also re-drilled the pilot and reground the entire
center when needed. IT's not an ideal solution, depending on the
condition of the diameter in the steady rest, it may come in to
tolerance, in our case .0002", or it may not. If the arbors were an
off the shelf item, buying new probably would have made more sense.
Some came in to nothing detectable with a .0001" indicator, others
would not come in to less than .001".

I would imagine that using a tiny point, and with enough rpm to turn
it, doing very small centers would be possible, not that I would want
to be the one to do them. PITA as it is.



On Thu, 8 Jul 2004 21:36:44 -0700, " Jim Sehr"
wrote:

How small a centerdrill could you grind?
Jim
wrote in message
.. .
On Thu, 8 Jul 2004 20:06:39 -0700, " Jim Sehr"
wrote:

I used to work in a gear shop and had to repair gear shafts that had been
centerdrilled and had more then the .001 runout that the print called
for.
I used a steadyrest with ball bearing rollers and that gave me dead true
runout. It is best to collet or chuck on a small part of shaft and let
the
steadyrest pull the shaft to dead true. Then I hand ground a 30 degree
angled tool to form one side of the centered part. Imagine half of a
centerdrill without the drill part in front of the angle. If you blue up
the
center of the part you can see it cut the high point of the runout till
it
is dead on.

In the last year or so we've had to recenter several inspection
arbors. Basically the same, except after putting in the steady rest,
we indicated the compound to 30 deg., then ground with a Precice
grinder, small CBN wheel. Used the normal bronze against the arbor,
gives less runout than BB would.
Lennie the Lurker


Lennie the Lurker