On Thu, 18 Mar 2004 12:13:05 -0600, Jon Elson
wrote:



Mike wrote:
Please help need some co-ax instructions...



Guessing that you have one of these knock-offs of the Blake Co-Ax indicator,
and need to know how to use it.

You need a rod that screws into the side of the body to keep it from
rotating.

As your run the spindle at dead slow speeds (ie less than 60 RPM)
a feeler wipes around the ID of the bore you are trying to center over.
If the bore is not very smooth and round, you will find it very difficult
to make the indicator work.

Assuming a round bore, the dial will wobble back and forth. By watching
the dial and the feeler at the same time (making the spindle run even
slower, maybe 25 RPM helps) figure out where the "high spot" is, and
move the table to pull that high spot away from the spindle. When you
get that axis right, the dial will read the same when the feeler is
touching points in line with that axis. Now, adjust the other axis
in the same way. When you get close, the pointer will only wobble a
few thousandths each way. Make very small movements in each axis to
minimize the pointer movement. At some point, you may not be able to
reduce pointer movement below some small amount. This is due to
a bore that is out of round, or possibly a bore that is not parallel
to the spindle rotation. But, the spindle should be as close to
coaxial to the bore as you are going to get.

Jon
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

Hey Mike,


On the very basic side of things, you chuck the shiny part of the
shaft (1/2" ??) in a collet or drill chuck, and put on the anti-rotate
bar and something on the mill for it to rest against so the "body" of
Co-ax Indicator is in a position where you can see it easy. A
magnetic indicator-holder and rod, stuck on the side of the mill
head, or even on the work-piece or table, will do fine. Anything that
stops the Co-ax indicator from being able to turn when the spindle
turns. Then extend the quill down to just above what you want to
locate on, and rough center locate on the work-piece with the X & Y
hand-wheels.

Now just the same as on any DTI, you put on a useful contact tip to
reach the hole sides (or the boss) and "bend it" so that as you lower
the quill some more it will enter the hole (or touch the boss) and
will deflect the Co-ax needle all the way around the hole (or boss) as
you turn the spindle. If you didn't get the "rough centering by eye"
part close enough, the Co-ax indicator will peg out, but it won't hurt
it. Of course, it won't do it's job until you get centered to the
point where it can make a full rotation with-out "pegging".

I don't use "power" to do the centering. Maybe because my J-head is a
step-pulley, and I'd have to fiddle around to get it in back-gear for
the slow RPM's, I've never spun mine under power. I just rotate the
spindle by hand to the four quad points and adjust the co-responding
axis at each. I try to get the centering as best as I can first with
these four point stops and gently moving the X or Y to see half the
deflection on the dial. When I think I have the four points set, I
try full and constant rotations and watch for "wobble". You are
looking for "zero" movement of the needle of course. Works for me.


Hey, .... Good Luck, and have fun. Neat to watch.

Take care.

Brian Lawson,
Bothwell, Ontario.