DoN. Nichols wrote:
[...]
But consider things like an old Singer sewing machine motor and
controller (such are are on the model 221 portable). It is simply a
DC/universal motor and a foot pedal which controls the current to the
motor (AC, but DC would work just as well). The foot pedal is simply
a stack of blocks of resistance element between two electrodes. The
harder you step on the pedal, the harder the blocks are pressed
together, and the lower the resistance, so the faster the motor runs.
I cannot imagine that a lot of torque was required of Singer sewing
machines. What hapens to torque at the lowest speeds?
You don't *need* the kind of regulation which the fancy
controllers give for this lathe. And you could use a pedal speed
control from a Dremel (from before Dremels came with built-in speed
controllers). I can't find the Dremel ones on eBay at the moment, but
this looks as though it might work as well. It is poorly described,
but
I expect a controller for a DC/universal motor.
Ebay auction # 260291509189
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).
The speed regulator is based on the speed a given motor is
capable of. It won't make motors not designed for it turn at 30,000
RPM. Find a 120V motor which is closer to 1000-2000 RPM and see what
happens.
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).
This sounds good -- until you mention later that it is a 12V
motor, not a 120V motor.
I got one of them drills, too. But again, what happens to the torque at the
low speed if using a rheostat? On mine there is a slow start feature which I
take to be nothing more than a rheostat. I can stop the chuck by hand at the
low speed.
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.
You want a drill which plugs directly into the AC line, not one
which runs from batteries.
I got a 13.6V 20A power supply - that's 1/3HP.
[...]
Oh -- you are thinking of two belts on each pulley except the
end ones. That restricts you to combinations which don't need the
same groove for both incoming and outgoing power. And I think the
lowest
speed with triple reduction would be both too slow for the size of the
machine and those tiny belts could not handle the transmission of
power over the last two stages.
63 rpm. But I take the point about the torque.
Use timing belt pulleys. Figure the largest diameter which
would clear the base when mounted directly on the spindle, and then
look for the smallest pulley of the same pitch which will mount on the
countershaft. At a guess, you might be able to get a 5" diameter
pulley plus the belt on the spindle (make sure that it is available
with a hub which matches the OD of the spindle at that end), and
assuming 5 teeth
per inch of circumference, that would be about 78 teeth. Then a
smaller pulley with 12 teeth would give about a 6:1 reduction in a
single pass.
O.K. Looking in McMaster Carr's web site, I find 1/2" wide belt
pulleys with a 0.200" pitch (MXL series). Let's see the largest
which will fit within 5" diameter.
The range for this size is 60 teeth max and 10 teeth minimum, or
6:1 ratio.
OD Teeth Bore Cat No Price
0.87" 10 3/16" 57105K11 $7.40
1.13" 14 1/4" 57105K14 $7.51
3.80" 60 5/16" 57105K33 $17.15
So -- if you need to fit it on a 1/4" shaft, you will need at leat 14
teeth (60:14 ratio, or about 128 RPM for 550 RPM in.
If you can turn the end of the shaft down to 3/16", you get a full 6:1
ratio, or 91 RPM.
These (and others) are on McMaster Carr's catalog page 1044 via
the web. (You'll also need to select a belt to fit including the
proper spacing between pulleys.) The pulleys which I have listed are
acetal plastic, and I would suggest that you go for the steel ones
listed a bit later in the page for stronger gears. And you'll
probably need to pin
the hubs instead of just use setscrews to get enough strength with the
small diameter shafts.
This would mean turning the spindle shaft down to at least 3/8". I do not
think this is possible.
AFAIK the spindle is 5/8" with a 5/16" ID. Some of
the plain bore pulleys have large enough bores but maximum of 24 teeth or
so.
It is beginning to feel like trying to make a silk purse out of a sow's ear.
Some limitations will have to be accepted I think.
12" swing,
Increased rigidity,
The Holy Grail...
--
Michael Koblic
Campbell River, BC