I am "working" on having a motorized feed for my lathe. The VFD control
on my drill press is SO convenient that I think it would be nice on the
lathe too. The biggest problem is getting the speed range, but I also
needed to know how much torque is required, for motor sizing.

I have already extended the lead screw on the tailstock end, so I made
an adapter that fits over that and has a 3/8" diam stub. I chucked the
stub in a cordless drill, set the DOC worst case, started the lathe,
then started the feed with the drill. As it was cutting I turned down
the clutch on the cordless drill until it slipped. That setting being
too small, I increased it one step.

I then took the drill and chucked up an L-shaped rod, with a 10" free
leg. Putting the end of that leg on a scale, I very slowly pulled the
trigger and noted the scale at the point the clutch slipped. It was 1
lb - 8 oz. Times the 10" arm gives 240 in-oz, or 15 in-lb torque.
Surprisingly small!

Admittedly, this is not a very precise way to measure torque, but it's
close enough for me. I'll probably double it when I come to chose the
motor needed, just to be conservative. YMMV.

Bob

Bob Engelhardt writes:

Admittedly, this is not a very precise way to measure torque, but it's
close enough for me.

Drill improvised into a dynamometer. Not bad.

I would consider a PMDC motor and speed controller instead of AC and VFD.
Better economics in this low-power size, and a gutsy low-speed torque
reserve.

XL or L belt and pulleys will solve the shaft alignment problem, while
allowing you to change the ratio if your torque target turns out wrong.
Will avoid slippage that will make your feed (and part finish) uneven.

Richard J Kinch wrote:
....
I would consider a PMDC motor and speed controller ...

I have been considering that combo. But I'm looking for about 30 rpm on
the lead screw and I don't know if that's doable. My short list
includes a cordless drill motor & gearbox.

XL or L belt and pulleys will solve the shaft alignment problem, ...

That's something new. How do they do that?

Will avoid slippage that will make your feed (and part finish) uneven.

Good point.

Thanks,
Bob

Bob Engelhardt writes:

XL or L belt and pulleys will solve the shaft alignment problem, ...

That's something new. How do they do that?

How were you planning to couple the motor to the leadscrew? You must have
some sort of coupling that transmits torque through misaligned shafts.
Belt-and-pulleys is one method. For direct methods:

http://groups.google.com/group/rec.c...f26dc704d6d31c

"Bob Engelhardt" wrote in message
. ..
I am "working" on having a motorized feed for my lathe. The VFD control
on my drill press is SO convenient that I think it would be nice on the
lathe too. The biggest problem is getting the speed range, but I also
needed to know how much torque is required, for motor sizing.

I have already extended the lead screw on the tailstock end, so I made
an adapter that fits over that and has a 3/8" diam stub. I chucked the
stub in a cordless drill, set the DOC worst case, started the lathe,
then started the feed with the drill. As it was cutting I turned down
the clutch on the cordless drill until it slipped. That setting being
too small, I increased it one step.

I then took the drill and chucked up an L-shaped rod, with a 10" free
leg. Putting the end of that leg on a scale, I very slowly pulled the
trigger and noted the scale at the point the clutch slipped. It was 1
lb - 8 oz. Times the 10" arm gives 240 in-oz, or 15 in-lb torque.
Surprisingly small!

Admittedly, this is not a very precise way to measure torque, but it's
close enough for me. I'll probably double it when I come to chose the
motor needed, just to be conservative. YMMV.

Bob

Am I missing something here???

It doesn't take much torque to simply turn the leadscrew (and, presumably,
move the carriage. But, when you are trying to take a heavy cut, the torque
can be pretty substantial...

Jerry

Jerry Foster wrote:
Am I missing something here???

It doesn't take much torque to simply turn the leadscrew (and, presumably,
move the carriage. But, when you are trying to take a heavy cut, the torque
can be pretty substantial...

I think that you did miss it. I can be too brief in my posts, so it was
probably easily missed: I took the torque measurement during a heavy
cut, the heaviest that I would expect to make (.050" DOC & .050 advance,
IIRC - it's not a heavy lathe).

Bob

I think that you did miss it. I can be too brief in my posts, so it was
probably easily missed: I took the torque measurement during a heavy cut,
the heaviest that I would expect to make (.050" DOC & .050 advance, IIRC -
it's not a heavy lathe).

Bob

for what it's worth, the manual for my logan PL92 lathe says that the clutch
slips at 900 pounds force



--
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William Noble wrote:
for what it's worth, the manual for my logan PL92 lathe says that the clutch
slips at 900 pounds force

YOWEE! Are you sure? There's a unit missing there, but even if it's
900 INCH-pounds, that's a LOT of torque (75 ft-lbs)!

Or maybe that's the axial force on the clutch plate. In which case it
really doesn't say anything about the torque.

Bob

On Sun, 13 Jan 2008 20:20:49 -0500, Bob Engelhardt
wrote:

William Noble wrote:
for what it's worth, the manual for my logan PL92 lathe says that the clutch
slips at 900 pounds force

YOWEE! Are you sure? There's a unit missing there, but even if it's
900 INCH-pounds, that's a LOT of torque (75 ft-lbs)!

Or maybe that's the axial force on the clutch plate. In which case it
really doesn't say anything about the torque.

Bob

Actually, it's 900 pounds of THRUST on the carriage.


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On Jan 12, 12:11 pm, Bob Engelhardt wrote:
I am "working" on having a motorized feed for my lathe. The VFD control
on my drill press is SO convenient that I think it would be nice on the
lathe too. The biggest problem is getting the speed range, but I also
needed to know how much torque is required, for motor sizing.

The manual for my Atlas-Craftsman 12x36 cabinet lathe (underdrive)
says to set the leadscrew safety clutch at 5 ft-lbs. It has only
kicked in once, when a chip worked its way into the apron gearing and
jammed the entire mechanism. I generally take fairly heavy cuts to
maximize productivity.

woodworker88 wrote:
The manual for my Atlas-Craftsman 12x36 cabinet lathe (underdrive)
says to set the leadscrew safety clutch at 5 ft-lbs. It has only
kicked in once, when a chip worked its way into the apron gearing and
jammed the entire mechanism. I generally take fairly heavy cuts to
maximize productivity.

That's really useful information, thanks! If 5 ft-lbs is the safety
limit on a 12x36, the 1 1/4 ft-lbs (15 in-lbs) that I measured for a
heavy cut on my 10x24 sounds realistic.

Thanks,
Bob