On May 14, 11:22*pm, "DoN. Nichols" wrote:
On 2009-05-14, Charles U Farley wrote:
Don Foreman wrote in
...
I don't know about your dividing head, but mine had a knurled
thumbscrew which will disengage the worm from the spindle, allowing you
to turn the chuck much more quickly by hand. It also has a ring behind
the chuck with a lever-controlled pin for simple dividing
(2/3/4/6/8/etc) so you don't even need the plate for simple dividing.

The exploded drawing shows a screw behind the index plate that may
lock the eccentric worm engagement.

My past experience has been that a three jaw is adequate for the class of
work done on items that require plain indexing cuts. For more complex and
higher tolerance dividing work like cutting gears the job was placed
between centers and driven with a dog. I've not had a project that
required the hold of a four jaw or accuracy exceeding a 3 jaw with a bit of
shim to correct chuck runout. ...

Personnally I've mostly done either lengthwise grooves or flats on a
shaft, between centers or in a collet, or cuts on or near the OD of a
disk which was centered on a mandrel and clamped to a faceplate. Two
examples are the tractor steering gear and a circular tee slot. I've
made a number of long adjusting screws by milling a hex on threaded
rod, which doesn't fit collets very well.

I bought some 5C-mount lathe chucks to index a turned part accurately
and found that they didn't hold securely enough unless I took very
light cuts. I didn't want to overtighten and damage them. The
instructions for the Sherline chuck warn that it's for light duty
only. If the shaft rotates while cutting flats one side jams into the
end mill. Then the belt slips and I weld up the gouge and regrind the
tool, but that would be expensive on a geared-head mill.

Some commercial jobs I've worked on were more difficult, the most
complex was a rotating ink jet print head somewhat like the crankcase
of a radial engine. I think the machinist made a fixture with
centering plugs to locate both sides.

If you use a faceplate you can clamp all around the edges and remove
each one to cut under it. You could center the work on a rod in the
center collet by making a cone that slides on it, or a slightly
tapered bushing for more precision.

jsw