Hi Ian,
I have seen bike handlebars done that way. My thoughts on such a
locking mechanism were more on a par with a masonry bolt. Slit your
close fitting shaft - even crudely with a hack saw - at every 90
degrees say. Then turn a cone shape to partially sit inside your
close fitting shaft as a spreader. Tap at 8mm for the draw bolt.
That should eliminate any misalignment during tightening. In either
case, during removal you need to loosen the 8mm bolt but NOT use it
to pull the close-fitting shaft out of the spindle as that would
tend to re-lock it.
Just a thought. Both approaches lend themselves to reversal. Turn
the 8mm bolt around and use an off-the-shelf nut on the outer end.
Key the inner end to the cone or wedge section by milling a slot or
pinning. This avoids cutting a long thread with any associated
angst. It also means both bolt & nut can be high tensile with little
chance of ever stripping and easy replacement anyway. Or were you
figuring on cutting the 8mm thread in the lathe?
John
--- In 7x12minilathe@..., "steam4ian" <fosterscons@...>
wrote:
G'day John.
You are lucky to have a significant length of thread left on the
end
of your spindle, I have next to none.
I don't see the expanding shaft as being too difficult, pull the
handle bars out of the neck of a bike to see what I mean. You
can't
make it longer than you can drill anyway.
I am now considering this for an indexer attachment using the
change
gears. What I plan is a close fitting shaft (to the inside of the
spindle) with a relatively steep taper towards the outboard end to
ensure centering. This would be turned down at the end to the gear
diameter and a key way cut in it. The whole would be drilled
through
to take a 8mm bolt. The locking mechanism would be two parts of
the
same diameter as the shaft(close fit in the spindle) made by
turning
down one piece then making an inclined cut through it. The
outboard
piece would be drilled through over size for the 8mm bolt and the
other drilled and tapped for the 8mm bolt. Tightening the bolt
would
force the two pieces to the walls of the spindle thus securing the
indexer. Being two pieces the opposing forces should not misalign
the
attachment too much.
This same method could be used to mount the hand wheel to the
spindle
without risking your spindle bearing preload. There would still be
room for longer work pieces or an excuse to use the steadies.
I must make a hand wheel/ crank to save using the chuck key in the
chuck as a tommy bar to rotate the work when taping.
One good turn (even by a crank) deserves another.
Regards,
Ian
--- In 7x12minilathe@..., "born4something" <ajs@>
wrote:
--- In 7x12minilathe@..., "roylowenthal"
<roylowenthal@> wrote:
The proponent of that is Mike Tagliari, he did it to allow
turning
long pieces with a handcrank. The only downside is having to
make
sure you don't move the nuts, changing the HS bearing preload.
Roy
And using a hand crank with a long bar poked through the middle
must
be a PITA. But a nice option when necessary. <G> Good argument
for
a
big cast valve wheel!
I just checked. My spindle has a full 4mm of thread on the
outside
of the locknut. That should be sufficient to attach a threaded
crank
onto which would tighten under load in the forward direction.
That
begs the question of how to secure it to allow reverse. Maybe a
pin
into a hole or a slot cut in the spindle end? To avoid loosening
the
spindle lock nut during removal a collet spanner could be used.
Thinking through the keyboard here. Is this the makings of a
viable
crank idea?
