On 2009-05-15, Jim Wilkins wrote:
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.

That could be it -- but IIRC, it is near the other end of the
worm screw from the hand crank and index plate. It both allows the
screw to be disengaged (it is in a bearing which is pivoted near the
index plate), and to be adjusted for minimum backlash when it is
engaged.

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.

Hmm ... I've made some by using a hex collet and hex stock,
turning the OD down using a box tool (in a bed turret) and threading
using a Geometric die head, then parting off. Very quick if you need to
make more than one -- slow to set up for the first one.

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.

Yep. My dividing head has a center with a T-bar just behind the
point. The T-bar is slotted parallel to the axis on each end, and
drilled and tapped for a square headed setscrew on each end. You set up
the work between centers, clamp a dog (also using the same style of
square headed setscrews) around the arbor or some direct part of the
workpiece, and then tighten one setscrew in the T-bar against the tail
of the dog so there is no give in the connection of dog tail to T-bar.

It also has a hefty three-jaw chuck which screws onto a 1-1/2x8
(or something similar -- I really need to check that again and make a
mount for the smaller 4-jaw chuck which I used to use on the old 2-1/4x8
spindle for the Clausing before I converted it to L-00 spindle nose.)

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.

And, of course, something to prevent rotation of the workpiece
relative to the dividing head.

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.

Right -- but I don't have a faceplate for the dividing head.
Perhaps I should make one of those, too. The thread should not be
difficult to turn using the Clausing.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---