"Dave Baker" wrote in
:


wrote in message
...
I'm locating the center of some holes .500" dia with a Starrett edge
finder.
The tip of the edge finder is .200. I'm just not sure if I'm doing it
the BEST way.
Maybe I'm missing something. Basically, I lower the tip of the edge
finder just inside
the hole. I then move the X axis until It touches. I then move the Y
axis until it's
not touching. Then back to the X until it touches. I keep this up
until rocking the Y axis
no longer provides any clearance. Then I move the X in .150 and zero
the DRO.
Then I repeat this process again for the Y axis. Basically, I'm
finding
the
tangent of the 2 axis.

Is this the way it's normally done? This takes me a long time
(inexperienced)
The only instructions I've found on line, tell me how to locate a
straight edge.

Any PRO suggestions appreciated.

RonL

You've got to be bloody joking. That's the most half arsed way of
finding a centre I've ever heard of. The geometry of chords says
you'll be miles out because it takes a large movement in the X plane
to make a small one in the Y plane as you approach the true diameter
of a circle. I know I've explained that extremely badly but I know
what I mean.

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.

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.

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.

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.

There's a bunch of other methods, any of which is better than the one
you've been using which is close to useless.
--
Dave Baker - Puma Race Engines (www.pumaracing.co.uk)




How about doing it the right way, and use an axial indicator......Amazing
how well those things work...since that is precisely what they are
designed for....


--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

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