On 11 Nov 2010 05:50:14 GMT, "DoN. Nichols"
wrote:

BIG snip

So, here is the result of 3 hours' work:

1) I found a dowel pin. At least I am pretty sure it is a dowel pin.
It is pretty and shiny, 0.5" x 6", it has those black caps either end
and on it it says USA made, 1/2". I do not know how I got it.

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.

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

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" !

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

7) The No. 4 at 0.007"

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

9) As the punch mark have definite dimensions I tried just locating
crossed lines. This is quite difficult: Just because you can see the
lines on the bench does not mean you will see them clearly under the
spindle, paint etc. notwithstanding. The results, confirmed with
center drilling , were considerably worse than center-finding a punch
mark, however small.

10) In view of the discussion spotting drills vs. center drills I
thought it made more sense to abandon using No.1 and No.2 and I used
No. 3 instead to make a small dimple with the pilot only. This should
approximate a starter hole produced by a spotting drill. This was a
definite improvement and the difference between the center drill hole
and subsequent 1/8" twist drill position was only 0.005" on the Y axis
only.

It should be noted that I used my machine screw length drills so the
actual distance from the chuck jaws to the point was pretty much the
same for both the center drill and the twist drill.

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.

12) Tramming:

a) The machine was out of tram to the tune of 0.008" over the X axis.
This was quickly corrected to 0.0005" with the head low. With the
head high this increased to 0.0035".
b) Moving the table along the Y axis produced no significant change. I
interpret this as the table being flat.
c) A spindle sweep in an arc from back to front, however, showed a
change of 0.005" over the 2" available in the Y axis. I interpret this
as the axis of the spindle being off in the Y axis plane.

Conclusions:

1) Do not use digital indicators for this sort of work.
2) Change the center drilling procedure as outlined above.
3) Grind a spotting drill?
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.
5) Consider acquiring better center drills.
6) Use collets whenever possible.
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 what it is. Like they say on South Park "I have learned
something today". I should be able to minimize the errors by being
aware of the pitfalls.

Thanks again for the help.

Michael Koblic,
Campbell River, BC