On Thu, 10 Jul 2008 22:44:21 +0000 (UTC), Hul Tytus
wrote:

rec.crafts.metalworking
measuring play in quill+spindle of milling machines & drills

I'm hoping that some here have measured the play in the quill+spindle
of bridgeport & equivilent millers, which will be a deciding factor when I
buy one in the future.
The measurements that I have made were by chucking a 10 inch piece of
bar stock and pulling 10 lbs left then 10 lbs right at the end with a spring
scale with the quill lock, when present, loose. A dial indicater set on the
spindle indicates the play.
A small bench size drill press, a $60 version, showed 13 thousandths
of an inch play, 8 for a full size and heavier drill press, and 5 for a
spanking new mill/drill from Harbor Freight. The last omitted the scale
which leaves it a bit questionable.
If anyone has made equivilent measurements, posting the results
here would be greatly appreciated.

Hul

There should be very close to zero play. Not more than a few tenths
between the quill and its housing, and none between the spindle and
the quill. What you've been measuring is play plus deflection. If you
were to plot your indicator reading vs. force applied, the play would
appear as a steep line starting at the origin; the elastic deflection
would be a relatively gentle and more or less straight slope. The knee
where the two parts of the curve join represents total free play. In
other words, play is the parts rattling around when small forces are
applied; after the free play is taken up, and you apply more force,
you're elastically deforming the machine.

Measure the quill play with the indicator base on the quill housing
and the point applied to the quill close to the housing. Try it with
the quill both locked and unlocked. Stick the indicator base to the
quill to detect spindle looseness. As much as possible, you want to
isolate what you're trying to measure.

The spindle runout, measured on the inside taper or with a known good
collet and pin, should be less than about 5 tenths. Perhaps a bit more
or less depending on what sort of work you expect to do. A good BP
spindle will be less than about .0002, though more may not be a
problem for non-critical work.

Any play in the spindle bearings in a mill is likely to cause trouble.

--
Ned Simmons