- posted 13 years ago
The dealer in the next town had a magnetic base and an indicator combo on
sale for $30. So I decided to make like a real machinist and bought one to
see what my various turning implements are doing.
First of all, I do not have a clue about differing qualities of indicators.
However, all the tests were done with this one, so hopefully if not
accurate, at least repeatable. I understand that using an indicator is not
straightforward but I tried to be careful to have everything clamped down
tight, the arm at 90 degrees to the surface etc. and I even tried different
positions of the indicator with similar results.
I tried my new drill press first. I put the indicator on the outside of the
chuck first and there was no more than 0.001-0.002" runout. Then I chucked
my biggest and bestest drill bit (3/4") and tried again. This time I got as
much as 0.015" runout. I tried rotating the drill in the chuck a quarter
turn at a time (re-chucking by tightening all three holes but not
excessively). The run-out varied between 0.010 and 0.015". I tried
differrent drill bits with very similar results, down to 1/8". I should say
that I tested by rotating the spindle manually holding the pulley.
I found I could bend the chuck 0.007" ether way without any tremendous
effort on my part.
I then tried the same but abbreviated test in my old cheap drill press - the
runouts were of the order of 0.007".
The reason I tried the drill bits is that I do not have anything round that
I am confident is machined to a close tolerance.
So a number of questions:
1) What is the expected stiffness of a drill press spindle? Is bending arc
of 0.014" to be expected? What would you expect in a mill? Or a lathe?
2) What are the expected tolerances of drill bits? Is 0.010" out of round
usual?
3) What are the expected tolerances of Jacobs 5/8" chucks? Is 0.010-0.015"
reasonable? I understand that 3-jaw chucks on lathes are not as good at
centering as manually adjusted 4-jaw chucks. Is this about the order of
things?
4) Given that the runout was of the same order throughout the testing would
you say that it is predominantly due to the chuck rather than the drill bits
being out of round?
Thanks,