On 12 Nov 2010 06:01:52 GMT, "DoN. Nichols"
wrote:

My WML hates you. It swallowed your post again. OTOH it is not
prejudiced, it swallowed my last reply, too.

[...]

2) In the chuck, using a different indicator from last time, the TIR
3/8" under the jaws, 2" and 4" respectively was 0.001", 0.003" and
0.006". Re-tightening made no difference.

O.K. The drill chuck, or its arbor is not true. Bent arbor, or
burred chuck jaw.

3) In a collet the figures were 0.001", 0.0015" and 0.002"

Better, but not perfect. How are your collets mounted? Since
you don't use R8, presumably you have a Morse taper shank socket and a
Morse taper holder for something like ER collets. (Or perhaps you are
using Morse taper collets?) I can't remember the details of your
machine at a distance like this. :-)

I did some repeats after the tramming today. The collets are Chinese
ER look-alikes on a MT3 shank.

Today the dowel pin run perfectly parallel at 0.0015" in a collet.

I put the No. 3 and 4 center drills in their respective collets and
they run at 0.001" both.

I put the chuck back in. The dowel pin run 0.002 at "zero" and 4"! But
then I repositioned it slightly and re tightened and the wobble
appeared - 0.004" at 4".

I tried the center drills: No.3 was better initially at 0.003", but re
tightening I could make it 0.005".

No. 4 was 0.007"

For the sake of comparison I put the dowel pin in my drill press:
0.0035" and 0.007" at "zero" and 4".


Anyway -- since there is runout with the collet, and still a
lack of parallelism to the spindle, check for burrs in the Morse taper
socket in the spindle. (Try spotting blue (Prussian blue) in a very
thin film on the Morse taper shank of the tool, then put it into the
socket lightly, twist a few degrees, and pull it back out. Check the
bluing for where it is rubbed off. If widely spread on one side, and in
a narrow location on the other side, then there is likely a burr in the
socket (which will need application of a Morse taper finishing reamer to
clean off). Or -- there *could* be a burr on the Morse taper arbor
instead -- patterns of blue built up around a clean spot could indicate
that, and require a little stoning to remove the burr. There could be
burrs on both the collet's arbor (assuming ER style collets) or the
individual collet (assuming a Morse taper collet).

I tried this with the chuck arbor MT3 taper. I got somewhat
inconsistent result but no large areas. Nothing I would want to attack
with abrasives remembering that I could screw things up rather than
help.

I thought it would be helpful to check the run-out of the JT33 arbor
and tried to remove the chuck. I made a wooden jig to support it but
it seems that the helpful Chinese glued the thing in so I desisted
before things got out of hand.

4) Repeat test with the same 3/8" drill I used before the TIR under
jaws was 0.001"

5) I tried my 3/8" reamer. Under the jaws the TIR was the same but
2-1/4" down the shank 0.0115" !

Reamers (assuming a chucking reamer instead of one with a square
tap wrench drive on the end) have a soft shank which can bend, so you
can't trust that for indicating runout away from the chuck.

A lesson learned...


6) The No. 3 center drill runs out at 0.008"

Weird.

7) The No. 4 at 0.007"

Again weird. This is in the chuck, or in the collet?

See above. I am beginning to think that the main problem is how this
chuck grips things in the jaws. I think it likes longer shanks. The
area between the flutes on the center drill is quite short. In a
collet it does not matter.

8) I repeated the center finding tests. the two instruments varied
sometimes by as much as 0.02"

Still using the chuck -- or the collet?

Chuck. I forgot to do the collet test today.

[...]

11) I cleared the table and returned to the dowel pin in the collet. I
used the machinist square and could not see any deviation at all. The
two squares I have pretty much agreed with each other. Note I did this
along the X axis with the spindle in 4 different positions. The table
is too small to do this effectively along the Y axis.

O.K. The axis is pretty perpendicular to the table, then. Did
you have a light behind the square and pin?

I put a piece of white paper behind.

[...]

1) Do not use digital indicators for this sort of work.

You had been using a digital one? I don't remember you saying
this. *Some* digital ones are more accurate than some mechanical ones.
The Starrett "Last Word" mechanical if the bias spring is not applying
bias throughout the range. (A bump on the side of the point can cause
it to skip in the spiral, so there is a major deadband in the range.)

I did the first time. It was a part of an existing set-up. They are
nice for some things, axis movement, measurements over 0.1", but for
this analog is better IMHO.

2) Change the center drilling procedure as outlined above.
3) Grind a spotting drill?

How about *buy* at least one, so you know what it needs to look
like? I recently got (from a sale flyer from MSC) a couple of 1/4" x 60
degree spotting/centering drills (MSC #FJ71332167). If the sale from
that flyer is over, the "FJ" won't do any good, and the price will be
back up to whatever it was.)

Probably right. Getting the point exactly co-axial is probably
something I could not do with a Dremel.

4) To locate cross lines on a work piece it seems preferable to use
optical punch first and then locate the center on the machine. This
probably makes center finder and spotting drill unnecessary and can be
done with a twist drill directly.

Probably -- especially with a drill with split points. For
larger standard bits, the chisel point may be wider than the dimple left
with the optical punch, in which case the drill is likely to walk away
from the punched center point.

In that case I would probably be drilling a smaller pilot hole anyway.

[...]

7) Ideally one should try to correct the spindle axis. From what I
read of others' experience this is very difficult with this machine.

It is certainly a source of error.

One has to consider at what point the error generated this way exceeds
that introduced by the operator.

Michael Koblic,
Campbell River, BC