Re: Semi-good high speed spindle idea? - Proxxon collet chucks

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Chris Horne" <chris@s...>
wrote:

>
> Irby,
> how low did you get your runout on your collet mounting ?

Chris, I ended up with no measurable runout of the machined part
using a .001" last word indicator. But I didn't have the "spindle"
mounted in bearings. If you look at the part I linked to as you read
this it will help. The part I made was to slip onto the shaft of a
stepper motor. I turned the end that slipped over the 1/4" motor
shaft first. After drilling the 1/4" hole undersize, I cut it to a
very light press fit with the motor shaft using a ball-end 1/8"
carbide mill turning in a toolpost grinder. I also roughed out the
outside of the threaded end that held the collets. Then I removed it
from the lathe and in the mill, drilled and tapped the two clamping
screws, and cut the clamping slot. Then back in the lathe, I turned
another piece of steel rod to exactly 1/4" diameter, fitting it to
the previous 1/4" hole as I went for a light fit. Then I clamped
the "spindle" part over the turned rod and finish cut the outside and
threaded it. I turned a centering hole in the end and used a live
center to steady the part as I cut and threaded the outside. I turned
the lathe by hand to do the threading, never releasing the half-nut
from the lead screw. Then I drilled the centering hole deeper and
just under the diameter required to hold the straight part of the
collet. I finish cut the ID and the taper with the same 1/8" carbide
mill in the toolpost grinder. I had measured the 30 degree angle for
the end of the collet, but as I cut it, I kept trying the collet in
place and made a slight adjustment to the toolpost slide angle to
make the collet bear evenly in the taper. I used a marker to see the
fit in the taper. I took a light skim off the OD of the rest of the
part while it was still in the lathe. Then I polished the diameters,
taper, and such with some 600, then 1500 paper. When I finished, I
measured the runout of the ID and of the taper, as well as OD back
near the 1/4" hole end, and the .001" indicator essentially didn't
move. I would turn and stop, turn and stop, and the dial never moved
from the mark. When I mounted the part onto the motor shaft, I could
see no increase in runout with the same indicator. I mounted several
drills in the collet and measured the runout of the shafts with
a .0001" indicator. It ran out .0002" max. on all of them. I had
measured around .001" runout of the Proxxon collets holding the same
drill in the Proxxon flexible hand spindle unit.

>
> In theory, the absolute best result is to machine the end of the
> spindle after it is mounted and driven, that way you can reduce the
> runout to a virtually unmeasurable amount.. machining it on the

lathe

> means the least runout you can achieve is the runout on the lathe
> chuck. Using the lathe I have not managed to fit the collet chuck

with

> less than 2 thou runout yet.
>
> One of my next experiments (when I get round to it) will be to
>
> 1. cut a cutting edge on the end of the spindle,
> 2. mount the spindle on the mill in the bearings it will run in,
> 3. severely preload the bearings to reduce runout to nil.
> 4. cut a hole using the spindle into a peice of stock mounted on

the

> table
> 5. drill the end of the spindle using an 8mm centre drill mounted

in

> the hole in the stock
> 6. cut the taper in the end of the shaft using the taper reamer I
> made previously. (it is already made from 8mm drill rod)
> 7. hand cut the thread for the collet nut.
>
> I am hoping I will then have a shaft with indetectable runout at the
> collet.
>
> Chris (-=Spiyda=-)

I agree you should do the final ID and taper machining with the
spindle mounted in it's bearings to get the lowest runout. Although
since the ID is a loose fit on the collet straight part, it's
concentricity may not be that important. The collets probably just
bear on the taper and don't touch the ID. But anyway, you may want to
try roughing out the ID and taper on the lathe as you machine the
rest of the spindle to match the bearings. Then hold the
spindle/bearing assembly by itself somehow so you can turn the
spindle and use the lathe carriage to finish machine the ID and taper
on the spindle. I would trust cutting the taper more than using a
reamer on it. I've never had good luck keeping near zero
concentricity with just a reamer. Same with drilling holes. I usually
drill under size and the finish with boring or, on small holes like
these, using the toolpost grinder and a carbide ball mill.
Theoretically, you should mark the bearings, housing, and spindle
radially so you can reassemble them in the same positions as you
final machined them if you take them apart.

Irby