"Dave Baker" wrote in message
...

You've got to be bloody joking. That's the most half arsed way of finding
a
centre I've ever heard of.

Well that was nice. I'll agree with you in that the original poster's method
was flawed, but what's with the attitude?


Do yourself a favour. Turn a couple of short lengths of 1/2" bar. Stick
one
in the hole (it must be a tightish fit) and one in the chuck. Bring the
two
into line and eyeball them up until they are closely aligned. Put a
straight
edge across the two and you can see a gap of less than a thou. Move the
bed
until there is no gap in either plane. You are now aligned over the hole.

Well, speaking of bad ideas...


Option 2. Stick a tight fitting 1/2" bar into the hole and fix a dial
gauge
to the milling head. Clock the bar up until you're concentric.

How do you count the number of sheep in a field? Count all the legs and
divide by four.

Perhaps he should just clock the hole?

Machine time is expensive and extra operations like turning a pin to fit a
hole so you can clock it is a waste of time and/or money.


Option 3. If you insist on using an edge finder (horrible bloody things at
the best of times) eyeball it up until it's fairly central in the hole.
Move
X right until it touches and zero the DRO. Move X left until it touches
and
note the reading. Split the difference. Move back to the centre and repeat
for the Y axis.

I would have reservations about using an edge finder on a curved surface...


Option 4. Stick a length of 1/2" bar in the chuck. Mount a dial gauge on
the
bed. Move the bed until the 1/2" bar goes in and out of the hole when you
move the quill down. Touch the dial gauge against the bar. When the bar is
perfectly centred the dial gauge won't move as the bar moves into the
hole.
If you're off centre the bar will still go in by forcing itself a bit one
way or the other but the dial gauge will show up the error. Jiggle until
you're centred in both planes.

I can appriciate that there are frequently many ways to perform an
operation, but this method introduces many errors and would be very
sensitive to operator error.

At work I clock holes because it's fast, accurate, and intrinsicly safe (as
in, no surprises).


There's a bunch of other methods, any of which is better than the one
you've
been using which is close to useless.

More encouragement for someone who would probably appriciate it and could
probably use it.

Regards,

Robin