Torque vs RPM?

[Berlin]

Hi all,

I'm a hand-tool guy who likes making his own tools and have a treadle or pole lathe on the cards, but I'm not a turner and would be interested to know what's more important in a lathe, torque or speed?

Obviously, I won't be able to approach a powered lathe on either count but if I had to preference one attribute which would it be? I could gear it generate higher RPM or I could beef up a fly wheel for greater torque, for example. I'm just mulling it over at the moment so any ideas you might want to throw in, please do ('don't be an idiot and just buy a normal lathe' is taken as a given ;) ).

Cheers

[jimbur]

Have you ever looked at Robin Wood's work?

[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. :rolleyes:)

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! :D

[Berlin]

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.

[Berlin]

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. :rolleyes:)

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! :D

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

[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.

[Skew ChiDAMN!!]

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 (http://www.woodworkforums.com/f8/ooh-ooh-ooh-got-me-new-lathe-41189/) 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! :rolleyes:

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... :think:

[Berlin]

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

[Berlin]

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?

[BobL]

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.

[Berlin]

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?

[jimbur]

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.:U

[Berlin]

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

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.

:U

[ian thorn]

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

[Paul39]

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.

[Skew ChiDAMN!!]

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

Yeah. Originally I was thinking of a simple weighted lever/pulley to tension it, but first I want to be sure I'm not making any other mods. I keep flip-flopping between keeping it fairly original and making it more versatile. (It's currently too slow to turn pens, for example.)


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.

And I suspect they're a lot easier to source too! :2tsup: Good thinking. It was an interesting experience to learn how to make my own belt; getting the overlaps & stitches flat and straight is a skill set all by itself. :rolleyes: But if/when the current belt needs replacing, I think I'll wander down to the automotive section instead. :wink:

[Bushmiller]

Is this the Robin Wood referred to previously? Lost out on speed (just) but cut the bowl deeper, so maybe not.

battle of the bowlturners - YouTube (http://www.youtube.com/watch?v=tDgIGzw4VtA)

Matt in regard to your original question perhaps you should just concentrate on developing your leg muscles, although I suspect that will be an ongoing development :wink: .

Btw, I thought everybody had a wooden cereal bowl :? .

Regards
Paul

[jimbur]

[QUOTE=Bushmiller;1609002]
Btw, I thought everybody had a wooden cereal bowl :? . /QUOTE]
Some of us stick to fine porcelain and Georgian silver rather than replica Elizabethan wooden bowls and spoons.:D
Yes Paul, it's the same Robin Wood.

[Bushmiller]

[QUOTE=Bushmiller;1609002]
Btw, I thought everybody had a wooden cereal bowl :? . /QUOTE]
Some of us stick to fine porcelain and Georgian silver rather than replica Elizabethan wooden bowls and spoons.:D


Jim

I understand. Even in this household there is discrimination . SWMBOs cereal bowl on the right and on the left......:( .

253452

Regards
Paul

[Berlin]

Oh Paul, that's not a bowl :roll: that's a Basque Chaff Box (page 382). You have a mighty appetite. Either that, or I have misjudged the scale in the photo and your wife eats out of a teeny weeny doll house bowl.
:U

Matt

[Berlin]

In reference to my original question: I am really pretty open to the option of a lathe with a tail, but I do like the idea of a person powered lathe and it's nice to see people like Robin Wood, Roy Underhill, Peter Follansbee ... and Skew ;) using them. I won't make any claim to huge ambitions as a turner but it's a skill I admire and would love to learn the functional rudiments of.

To that end: does anyone have any argument for a pole lathe over a treadle? I assume the orthodoxy is the other way 'round, but are there things theoretically possible on a reciprocating lathe that aren't possible on a normal lathe?

Thanks for indulging a novice :)

Matt

[Bushmiller]

Oh Paul, that's not a bowl :roll: that's a Basque Chaff Box (page 382). You have a mighty appetite. Either that, or I have misjudged the scale in the photo and your wife eats out of a teeny weeny doll house bowl.
:U

Matt

:) Matt

I did use a little, but not much, licence there in that SWMBO's bowl is a desert bowl, which does tend to be a little smaller, but my bowl is big :D. And heavy as it was made from ironbark by my son. I do use it every day, but I don't have the heart to tell him I can't afford to fill it up :- . A fist full of natural meusli looks rather lost in the bottom.

I have to be careful I don't drop it as I think it would go straight through the timber floor.

When you build your lathe we can expect to see a whole dinner service in timber? :wink:

Regards
Paul