DoN. Nichols wrote:
Ah. Did not think of No.1.

You should *always* consider what might fly out when you could
be in the path.

As my old boss used to say: "You can recognize it only if you think of it."

Someone else suggested a light dimmer which is typically quite
inexpensive -- and as for motors -- a cheap hand held electric drill
could be clamped onto a shaft in bearings to drive at a lower speed.
Or -- you could salvage a motor out of a vacuum cleaner or a kitchen
blender or anything else with a DC/universal motor. (Just look for
brush holders to verify that it is not AC only -- and the holders may
be hidden inside, as is common in cheap hand held electric drills.)

1) I might be wrong but the DC motor controllers usually have a feed back
which will increase the power in response to loading conditions. I do not
see a light dimmer doing it.

2) A router speed regulator is a thought, however, typically these motors
turn at 30,000 rpm give or take so major gearing would still be required.
And I am still not sure about the feedback thing. Some routers have it built
in now (EVS).

3) I have a DC motor from an old Sears drill sitting somewhere. As it stands
it would also need the whole gear box to get the speed down to something
useable. The speed regulation with it is basically the slow start. When it
is turning slowly there is hardly any torque which brings me back to (1).

4) It is a thought to make a controller along the lines in (1) for the
motor. However, given that the motor is a 12V one I usspect that the current
at the lower speeds would be appreciable.

[...]

I was thinking of just getting two more Taig pulleys ($24.49) and
making *two* countershafts.

Two extra pulleys (and an extra belt) would make *one*
countershaft, not two.

How is that? One pulley=motor. Belt to second pulley=countershaft 1
(reduction by factor of 3) Belt to third pulley=counteshaft 2 (reduction by
factor of 9). Belt to spindle pulley (reduction by factor of 27). A single
coutershaft would require pulley 2 and 3 to be on the same shaft with no
reduction of speed between them.

The lowest speed would be just over 60 rpm.
Even with just one pulley the speed would be under 200. And the
theoretical maximum speed of 47,250 rpm. I wonder what the 3-jaw
chuck sounds like at that speed...

Hmm ... what *is* the sound of a 3-jaw chuck flying into pieces.
That speed (if the motor could put out the needed torque) would
certainly explode the chuck. A 12" chuck is considered dangerous at a
bit over 3000 RPM IIRC.

Or 2 rpm if dropped from a second storey window.
I know what sound a hockey puck travelling at 80 mph makes. I almost wish I
did not...

The two questions that bother me about the concept of a countershaft
a

1) Is the 3M belt big enough withstand the torque at the lowest
speeds? Or would one have to go to a completely different
transmission for the final step (countershaft 2 to spindle), e.g.
timing pulleys and belt?

I would suggest that you make a timing pulleys and belt for the
step from the countershaft to the spindle to handle the extra torque.
Look for pulleys for about a 6:1 ratio which will get you down near
100 RPM or a bit more.

Yes, that appears to be the consensus.

2) If one were to make a pulley, how critical are the groove
dimensions?

The angle between the walls is critical, and the spacing has to
be tight enough so the belt does not touch the bottom.


The only pulley I made was the wooden one (and it works just fine)
but the process can hardly be repeated with aluminium (or can it?)

It could be -- but a lot of careful filing. And it will take a
lot longer than doing it on the lathe. You will either need a
compound set to make the proper angle for the walls, or a form tool
ground to cut both angles at the same time. And I don't think that
your machine can handle the amount of metal removal involved in a
form tool, even for that small a belt groove.

Agree. I have demonstrated it with the first parting tool. In any case your
comments above re-timing pulley make this issue probably moot.

And bear in mind that the speeds I give above are with no
slip. It will be slower with normal slip. Fore example, the 1650
RPM motor would be 1800 RPM with no slip. (900 with no slip becomes
something like 825 RPM with slip, and 600 with no slip becomes 550
RPM with slip.) That 550 RPM would get you down to 316 RPM with
your existing gearing.

Ah, with slip I can get down to zero, no problem...

Yes -- you can get down to zero -- but between zero and a bit
below the nominal speed with slip you will have no torque to work
with, so the descent from normal slip to zero will be very sudden.

Also do not forget the smoke...

But a DC motor a Variac, and a rectifier would be more flexible,
giving you a much wider range of speeds, and the ability to change
the speed in mid cut without having to stop the motor and change the
belts.

That is clearly the preferred option but the prices I have seen so
far really make it uneconomical.

An electric drill motor (a hand-held electric drill is called a
"drill motor") with variable speed hooked to a shaft mounted in
pulleys should do it -- until the drill motor burns out. They
typically don't handle long run times well.

[...]

Interesting. I get rather quiet parting even with 3" diameter
stock -- but I'll probably be running at about 210 RPM.

Maybe I should reduce speed...:-)

And increase rigidity too -- which is another feature of my 12"
lathe which you don't have.

Story of my life...

--
Michael Koblic
Campbell River, BC