On Jun 26, 8:17*pm, "DoN. Nichols" wrote:
On 2010-06-26, Searcher7 wrote:

On Jun 25, 12:10 am, "DoN. Nichols" wrote:
On 2010-06-25, Searcher7 wrote:

* * * * [ ... ]

There, one of the threaded holes would get a short bar screwed
into it with a large ball handle on the end for tightening and
loosening. (Not when using it in a rotating chuck of course, because
the handle would unbalance things -- unless you had three identical
handles screwed in at 120 degree intervals.

Actually, that would be four at 90 degrees.

Oh -- eight holes total, not the six I thought there were? I
never had a view which made it truly clear.

Yes, eight. Every other hole is threaded.

* * * * O.K. *I knew that every other hole was threaded, but I somehow
thought that there were a total of six holes, not eight.

The small bar I still think might be used to turn the small ring
onto the end of the collet and back off.

There is no place for the small bar. The ring that threads onto the
rear of the collet is solid, and actually threads about halfway on
before it bottoms out.(But I assume that is enough).

The small ring has a series of depressions around the OD. If
the spacing between that and the wall surrounding it is just right, the
pin on one end could be slid into a depression and used to chase it
around with the outer wall keeping it engaged.

The small ring is knurled, but that is all.

* * * * But is it knurled deep enough to allow the pin on the end of the
small rod to act to spin it on or off?

Well, I guess so, if I wanted to damage the knurls, but the rod is not
a tight fit, and I could just as easily use a screw driver, dowel,
etc. In fact I can get the ring on tighter with my fingers while press-
turning it.

* * * * * * * * * * * * * * * * * * * * * * Nevertheless, I can thread
it onto the rear of the collet with my fingers. But like I said it
will bottom out when it is approximately halfway on.

* * * * Sure -- you could probably thread it on a little more if you
were pressing in the collet nose while installing the ring, but that
would limit the size range of the collet.

Well, if I pressed hard enough to hurt my fingers it would turn
perhaps 1/16" more.

No! You would create an adaptor which mounts on the spindle
nose which has a cylindrical bore which is a slip fit for the OD of the
device, is deep enough to hold the body, but to leave the large black
ring accessible, and with a thin slot along the length of the bore and
some means of compressing it to hold the body.

Like a large collet or split bushing I assume. (Since the body of the
collet chuck is 2.75" long that would be a deep seat).

Yes -- except that the bushing would mount directly on the
spindle nose instead of through an adaptor.

Thinking about the material, thickness, and shape of this bushing, if
would appear that it would have to be made up of two main parts.

* * * * I see it as only two parts -- a cylinder perhaps an inch larger
in diameter than the holder body, and a screw threaded in to close the
slot. *(Oh yes -- also the studs to mount it on the spindle nose and the
corresponding nuts. :-)

* * * * But it will need a tricky bit of work to cut the slit along one
size to allow the screw to clamp it onto the body. *You'll need the mill
and some way to mount the rather large piece of metal to do that.

How about three slits in a tapered sleeve that is bolted to the
spindle. The sleeve would be slightly thicker at the front end, and at
the base there would be a tightening collar that is I.D. threaded at
the rear and rounded at the front end? Screwing it forward would
tighten the sleeve around the collet chuck.

Or perhaps a collar with a circular wedge that would be put on the
collet chuck body before inserting the body into a solid sleeve that
is bolted to the spindle. This way the collet chuck would seat first
and then the collar would be screwed back resulting in the circular
wedge sliding between the collet chuck body and the solid sleeve.

So here is the problem. What is to keep the front of the collet chuck
from rotating clockwise relative to the body under cutting forces,
which would result in opening the collet.(And making things really
exciting). :-)

Well ... normally the anti-rotation pin is not expected to
handle much torque -- but here it might have to.

Can you verify which direction of rotation closes the collet
(moves the large black ring away from the body)? Is it left-hand thread
or right-hand thread? If it is a left-hand thread, the cutting forces
would *tighten* it, thus preventing your problem.

Turning it clockwise will screw it onto the body.

* * * * So turning forces would normally loosen it.

* * * * * * * * * * * * * * * * * * * * * * * * * But I can understand
what you're saying. (I'm probably just worried too much).

* * * * I think that within the normal size range of the collets, it
would work. *If you went to one of the pot chucks that would be a
different matter.

If not -- then it is likely intended to hold a workpiece on a
surface grinder or other low force operation.

[ ... ]

Again -- forget it. You're thinking of the large black ring the
wrong way. It *has* to be free to turn so you can loosen and tighten
the collets.

But how does one keep it from turning under cutting forces?

Pray that the anti-rotation pin works? Look for a place where
the small pin slides into to prevent it from turning? Add provisions
for clamping the ring to the sleeve which holds the body? Run your
lathe spindle in reverse? (I think that is not an option on your lathe
anyway.)

Yes, reverse is an option. But I think that this would probably be
secure enough either way. Especially since it was no doubt made for a
more powerful machine than I have.

* * * * Certainly for the size range of 0.750" on down I see no problem.
Light cuts up to the 1.125" maximum should work as well.

So it comes down to this. Should I proceed with this collet chuck or
concentrate on the idea at this link:http://www.sc-c.com/metallathe/MLA21.html
(The MLA-21 would seem to be the best way to go).

* * * * I agree that the MLA-21 would be the better choice. *What
remains to be seen is how difficult the machining is to make it from the
castings.

* * * * Why not buy the drawing first to see what you will have to do.
The "lathe only" construction suggests that the side clearance holes for
the tommy bar access to the ring would be part of the casting -- though
a mill and a dividing head might be used to dress up the edges a bit.

* * * * Checking -- yes you still get partial credit for the drawings
which you purchased if you order them first, and the casting kit without
the drawings later.

* * * * One of the things which I consider best about this is that you
can mark the spindle and the casting where they join prior to turning
the closing taper and bore for the collet, so you will get the best
repeatability.

I'm starting to think that this should be my first project.

I attempted to take the lathe out of it's box today. Unfortunately it
looks as though I'll have to tear the box off around it. Something I
didn't want to do until I could put it in it's permanent location.(So
I won't be able to open the headstock just yet).

And instead of using the ring at the rear of the chuck, I'd use a
drawtube, if I can modify the machine to use a modified 5C spindle.
(Just throwing out ideas). :-)

You can't make your current machine have a large enough through
diameter to work that way. For a 5C collet closer, you need at least a
1-3/8" through bore, not your near 3/4".

Yes. That is why I am investigating installing a 5C spindle. I just
may have to shorten a drawtube shortening one. And the worse case
scenario would be a need for a different set of gears, if I can't
enlarge the center hole of the existing ones that directly drive the
spindle the spindle.

Of course I'll have to open up the headstock so I can see and measure
what is possible.

I expect that you will find that the entire OD of the spindle is
smaller than the needed bore through the spindle for a 5C collet closer.