On Wed, 7 Mar 2012 00:06:21 -0500, Wild_Bill wrote:

I'm not sure that I could find a picture of the type of hand crank
attachment I made, but I'll try to describe the methods used.

Turn a length of stock to within a couple of thousadths of the ID of the
spindle (ID minus ~.002") and long enough to reach into the spindle maybe
about half the depth.
The stock should be long enough to have a shoulder just outside of the end
of the spindle, and a suitable amount of remaining stock for the attachment
of a handle/crank (flat bar stock or handwheel with a speed knob).

Drill a center axial hole into the stock that includes the full length..
which may require drilling from both ends (depending upon available length
of twist drills).

The stock then needs to be cut at an angle (a little less than 45 degrees
worked well), so that when a bolt/stud passing thru the hole draws the two
pieces together, the angled cut causes the parts to shift off-axis,
expanding in the spindle to securely lock it in place.
The sharp edges around the angled cut of both pieces should be rounded over
with a file so as to not cause digging or gouging inside the spindle bore.

The ends of the holes nearest the angled cut can be filed out-of-round or
oval shaped to allow the shift to take place without too much tightening of
the bolt/stud.

A stud can be threaded into the shorter end (deepest in the spindle) in
tapped threads and staked to lock it in place, or pinned etc. and the stud
extends outward to the left passing thru the longer section enough to allow
a nut to be installed on it.

So, with the shoulder of the longer section against the left end of the
spindle, there should be ample stock sticking out for attaching the
preferred handle/crank.
As the nut is tightened firmly but not extremely tight, the angled cut
causes the two sections to wedge securely in the spindle bore.

I understand. Nice clear description.


I tried using a split expanding collet type of locking bar (quartered
sections), but it didn't grip as well as the second model utilizing the
wedge type bar.. which doesn't mean that it wouldn't be a good choice for
others.
I think the wedge type is actually easier to fabricate, though.

It is interesting that the expanding collet didn't work as well.
Torque-holding ability ought to be proportional to the outward force,
which ought to be greater with the expanding collet because it
probably has a much shallower angle than 45 degrees. Probably there is
some secondary effect that I am not thinking of.

One caution about using an expanding bar in the spindle, would be to only
tighten the nut enough for a secure grip in the spindle bore.
Some lathe spindles can be somewhat wimpy as far as wall thickness, so
over-tightening an expanding accessory with a grunt could potentially
distort the spindle.

The scale of the Prox lathe being somewhat small, may present more of a
challenge than the spindle bores of my machines, where I could use a 1/4"
diameter (or larger) stud to draw the wedged sections together.

The 230 model specs show a 10.5mm spindle bore which is considerably smaller
than the bores in my machines, so a different method of attachment may be a
better choice.. it's difficult to try to determine what other methods may be
suitable without knowing what features the spindle may have at the left end
(smooth OD, threaded, locking collar etc).

The left end has the "spindle gear" (actually a timing belt pulley) at
the end, with essentially no free space beyond it. In normal turning
the belt is on the outer end of the pulley. For screw cutting it sits
a little further in, some one could think about clamping a handle to
the pulley, but that is a little worrying, and besides there are two
different pulleys for inch and metric threads.

It think that the inside bore is the only attractive scheme.

Bob