Thread: Torque vs RPM?

Have you ever looked at Robin Wood's work?

Torque allows you to remove a lot of material quickly with only basic tool control.

Speed allows for cleaner, smoother 'finishing' cuts. (Or, at least, so it seems to me.)

If I had to choose I'd go for speed over torque. Lots of small fine cuts will give you a nicely finished product... eventually. Quickly roughing out a form doesn't get it finished any faster if you have to spend several hours sanding.

Personally I prefer a pulley driven system, where you can trade off speed for torque - or vice-versa - as needed.

(I'm not a big fan of electronically controlled 'direct drive' motors... but I've no real experience with the latest generation. )

When applied to a 'manual' lathe, there's no reason not to have a large fly-wheel connected to pulleys; my treadle lathe (and most others I've seen) do!

Originally Posted by jimbur

Have you ever looked at Robin Wood's work?

Yeah, someone else pointed me in his direction too. Very interesting.

I see he has written 'the definitive book on wooden bowls', which sounds like a real page turner. :P

Top work though.

Originally Posted by Skew ChiDAMN!!

Torque allows you to remove a lot of material quickly with only basic tool control.

Speed allows for cleaner, smoother 'finishing' cuts. (Or, at least, so it seems to me.)

If I had to choose I'd go for speed over torque. Lots of small fine cuts will give you a nicely finished product... eventually. Quickly roughing out a form doesn't get it finished any faster if you have to spend several hours sanding.

Personally I prefer a pulley driven system, where you can trade off speed for torque - or vice-versa - as needed.

(I'm not a big fan of electronically controlled 'direct drive' motors... but I've no real experience with the latest generation. )

When applied to a 'manual' lathe, there's no reason not to have a large fly-wheel connected to pulleys; my treadle lathe (and most others I've seen) do!

Thanks Skew, just the info I'm looking for! Do you have pics of your lathe? I'd love to see how you've tackled it.

Cheers

Removal of a a specific amount of wood will require a minimum amount of power.

Power = Torque x rotational speed,
or more specifically
HP = Torque (ftlbs) x RPM /5252

To achieve a specific power you can choose to have high torque/low RPM or vice versa.

In practical terms SCD's comment on finish is important.

Hiya Berlin!

I didn't make mine myself; it's an old ship's lathe from some time around the late 1700s. I think.

I don't have any recent pix, but I posted a few when I first bought it in post #1 of the ooh-ooh-ooh-got-me-new-lathe thread. (2006? I bought it that long ago?)

The drive belt wraps around the fly-wheel and, obviously, up over the small brown pulley on top. This pulley can be changed for others of different radii to change the speed, although it can be quite fiddly trying to get the drive belt tensioned properly again.

If I was building it for myself I'd add a lay shaft into the drive-train, with one end driven by the fly wheel and a pulley cluster at the other end, to drive the headstock. It'd be much quicker to change speed then. It'd need careful selection of the pulley sizes though... it is only one me-power after all and it'd be soooo easy to gear it down to something I just couldn't treadle easily!

I have also considered yanking the reeve's pulleys from one of my MC-900 type lathes, for 'on-the-fly' speed changes instead of using a pulley cluster. Might still try that, although it means mucking around with keyed shafts...

Wow. That's a sweet ride you've got there!

I won't pretend I understood all of mods you suggested but I have an idea of where to start.

Cheers

Originally Posted by BobL

Removal of a a specific amount of wood will require a minimum amount of power.

Power = Torque x rotational speed,
or more specifically
HP = Torque (ftlbs) x RPM /5252

To achieve a specific power you can choose to have high torque/low RPM or vice versa.

In practical terms SCD's comment on finish is important.

Hi Bob,

I see what you mean. The question is how I develop the appropriate power not the torque or speed separately. But the higher the RPM the smoother the finish. (operator skill not withstanding)

Is that right?

Originally Posted by Berlin

Hi Bob,

I see what you mean. The question is how I develop the appropriate power not the torque or speed separately. But the higher the RPM the smoother the finish. (operator skill not withstanding)

Is that right?

Sure but high RPMs has its own problems particularly with large objects.
This is why high rpm works well for spindle type work but the low RPMs that limit turning of large objects have to be compensated for by higher torques.

Ok. Thanks very much for the info Bob. I can see how that all works.

As a related aside, a large diameter blank would presumably have a lot of momentum once up to speed. Is the action of this 'extra fly wheel' of any significance?

Originally Posted by Berlin

Yeah, someone else pointed me in his direction too. Very interesting.

I see he has written 'the definitive book on wooden bowls', which sounds like a real page turner. :P

Top work though.

A member of this site eats his breakfast cereal from one of Robin Wood's bowls.

Originally Posted by jimbur

A member of this site eats his breakfast cereal from one of Robin Wood's bowls.

Just his breakfast cereal? That's a very specialised bowl. There's probably a chapter in the book about them, tracing cereal bowl development from Roman times with pointers on how to avoid confusing, say, a Saxon grule dish and an Alpine birscher muesli bowl.

Hi Skew just had a look at your lathe just a thought you could put a tension pully in the system that would help when changing drive pullys to keep the belt even

Cheers Ian

Hi Skew,

Lovely treadle lathe. An automotive serpentine belt works fine in place of a leather one. They do not slip or stretch.

Of course they are not original equipment.