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Dr. Rob
11-22-2002, 01:48 AM
...about speed control on the bench lathe.

Wanted this for ages, and have considered various electronic tricks (Model Engineer's Workshop for example has an article about using components purloined from a washing machine) but the result is always the same: Circuit boards put me to sleep. Completely meaninless to me; you can look at one for hours, and nothing happens. Nothing moves. (Although they look kinda cool- they look like satellite photos of small cities).

So I was thinking about variable speed V-belt pulleys, the expanding ones. Why not use one of these? Because of the loss of torque.

Okay then, is there any reason to not replace the existing 1/3 HP motor with something bigger, like 2 HP, to provide ample torque, and then use an expanding pulley trick? If so, why have I not heard of it?

11-22-2002, 07:29 AM
Well, I seriously doubt you need a 2hp motor on a bench lathe, but the variable-speed pulley idea is certainly nothing new. I think the Rockwell lathe uses (used) it.

Why do you think you'd lose torque, any more than you do with the regular setup? It shouldn't make any difference whether you use a variable-speed pulley setup, or regular step pulleys.

Personally, I'd go with a 1/2hp 3-phase motor and a variable-frequency drive.

Oh -- it would really help if you'd put more explanatory titles on your notes. "New Thread..." doesn't tell us much.

Dr. Rob
11-22-2002, 07:48 AM
The torque thing? Because I'd also like to do without the intermediate pulley for the low speed ranges. It may be impossible, since the range of the expanding pulleys just won't allow it. But, ideally...

The post titles? Yes, I'll admit they are sometimes a little obscure, but I'm under the impression that many folks click on them out of curiosity anyway. Like movie titles. (Saw 'Oceans Eleven' yesterday. Silly title, silly movie.)

Besides, you fell for it!

11-22-2002, 07:53 AM
Unless you are looking for another project to do, I would recommend that the best way to achieve speed control for your lathe is to install a 3-phase motor and a VFD. A somewhat larger HP rating than you are using now wiould take care of the slight fall-off in torque at very low RPM, and most VFDs will provide infinite adjustability of the motor with just fingertip adjustment or digital entry from a keypad. It sure beats the mechanical arrangements for speed control.

I have installed a VFD on both my lathe and my mill/drill, and find the resulting ease of control to be great. I am using two Mitsubishi VFDs. Other makes would be comparable and price/availability has improved significantly . . . sources such as Dealers Electric have both motors and VFDs at reasonable prices and specs.

Good luck.

Rich Kuzmack

Pi = 355/113 . . . to
<85 parts per billion

11-22-2002, 10:16 AM
I got a 2hp DC motor and speed control off a treadmill for just such a purpose. I just don't have the lathe anymore(12 inch Logan)It seems a little too large for my SB, but I might try it out anyway.

Don Clement
11-22-2002, 11:25 AM
I have two 12" lathes; a Rockford Economy belt drive lathe and a Birmingham 12x36 geared head lathe. The Rockford came with a 3HP 3phase motor. I originally used a phase converter and ran the Rockford 220V single phase. I then made a rotating phase converter from a 5HP 3Phase motor. Surface finish using the Rockford lathe was greatly improved using the rotating phase converter which generated almost true 3 phase. Some examples of the surface finish from the Rockford can be found on an old web page: http://www.inetworld.net/clement/cabledrive.html
I would suspect that a 3Phase motor and VFD drive would give similar results.
Surface finish on the Birmingham with a 2HP single phase motor is not so good. Seems to be phonographing due to the pulse nature of single phase motors. An analysis could be done to determine if the frequency of the phonographing matches the gears and speed of the motor. I am thinking of either replacing the single phase motor with a 3 phase motor with VFD or a 2HP DC variale speed motor.

Don Clement
Running Springs, California

C. Tate
11-22-2002, 12:32 PM
buy a new lathe.... thats the best way to fix it

Don Clement
11-22-2002, 01:28 PM
<font face="Verdana, Arial" size="2">Originally posted by C. Tate:
buy a new lathe.... thats the best way to fix it</font>

Are you talking about the Birmingham lathe? I have owned this Chinese made lathe for a couple of years. The Birmingham great lathe for the money. The three things that I didn't like about the lathe were: 1. no carriage stop 2. small footprint on lathe stand 3. single phase motor. I solved 1 and 2 by making a micrometer carriage stop that clamps to the pyramidal way and built outriggerers that tripled the footprint of the stand. Last item is to replace the single phase motor.

Don Clement
Running Springs, California

metal mite
11-22-2002, 02:49 PM
Dr Rob,
Why don't you rig up that mechanical variable speed drive (Reeves Drive),
write a an artical, and create prints, and we can all enjoy reading how it's done in H.S.M.

Dr. Rob
11-22-2002, 04:44 PM
Meaning what? That you are tired of reading it here and want this thread to die? Okay..

But lastly, the question I wanted to get to was, if variable pulley drives are so good and easy and cheap, why don't all machines have them right out of the box?
VFD's are comparatively expensive, no?

Ragarsed Raglan
11-22-2002, 05:01 PM
Dr. Rob,

Here's one way it was done in the past (1950's), on the Raglan lathes from the UK:-


There's a lot of images on this page so it may take a while to load.

The lever on top of the headstock controls the spindle speed. The range using back gearing was 35 - 2000 rpm. I've also added a VFD running a 3 phase motor on mine ~ so now I can get down to about 10rpm, still with enough power to die 3/8th steel bar, and up to about 2500+ (I limited the VFD to 70Hz max ~ UK supply AC is 50Hz).

I agree with the comment about 3 phase being smoother running than single phase ~ if it wasn't I'd be worried!! I went for a 1.1Kw motor (1.5HP)

I know where there is a nice Raglan for sale (NO it's not mine!!), should you be interested!?


[This message has been edited by Ragarsed Raglan (edited 11-22-2002).]

Peter S
11-22-2002, 05:23 PM
Dr Rob,
I don't think the torque available at the chuck will be different from any other speed reducing/increasing method.

I know of two lathes that use variable speed - Colchester "Chipmaster" uses a Kopp system, and Graziano 12S uses a Reeve drive. One problem with the reeve drive is - the pulleys must be rotating before you can adjust the speed. So what happens if you have it on max. speed, and want to start on the lowest speed? Well, the Graziano system seems to have the Reeves drive running constantly, with a clutch (actually two clutches, forward and reverse, plus brake) to disconnect the drive to the spindle and allow the drive speed to be altered while the spindle is stopped. BTW, the pulley is moved by a small servo motor, so all controls are by switches on the apron.
You can also alter speed while the spindle is engaged.
So a system like this is not that simple, but I think, on a serious lathe, you need to be able to alter the speeds while the spindle is stopped. So it is not as simple as just fitting a Reeve drive between motor and spindle (although you may get away with it on a small lathe, and I have a drill press and a band saw that work like this).
The Graziano also has a backgear, so the Reeves drive has two ranges, 55-360 RPM, and 310-2000. You can also get a two speed motor to widen the range further.

Will send you a photo of the Graziano 12S system.
2nd thoughts, I can't unless you send me or post an e-mail address!

[This message has been edited by Peter S (edited 11-22-2002).]

11-22-2002, 11:11 PM
Dr.Rob - The Delta variable speed drill press uses an expanding pulley arangement, or two, for a High/Low speed and variable within each. It works very well on the drill press, something like 150 to 3200 RPM, claims full torque at any speed. Maybe parts from Delta could be used for your lathe drive.

11-22-2002, 11:24 PM
Dr. Rob:
Sure you can make a variable dirve pulley set, but why?

It is far more cost effective to just go with a 3Phase motor and VFD. You will get smoother power and have enough money left for a year's worth of Viagra - so you are always up to the lathes level of performance. http://bbs.homeshopmachinist.net//biggrin.gif

Dr. Rob
11-23-2002, 09:12 AM
Thanks, Ragarsed for the link; I'll download that in a minute. I'm afraid I live too far away to make it worthwhile to buy a Raglan.

Peter, thanks for the photo offer, but things like that are disaster to my Hotmail account; Redlines it every time.

And Thrud, my little sweetheart of a lathe needs no additional help to get my interest...
Why? Oh, I don't know...I guess I just like the idea of speed control rather than changing the belt around, and I guess I like mechanical better than electronic. But You're right; it is probably easiest. A while back I bought a motor (3-ph x 0.5 hp) and a speed control thing of apparent expensive manufacture from a commercial ventilation fan guy. Speed control works, but not the torque thing. Don't know why.

One more thought, since I don't know anything about electronics...Remember sewing machines? They often have a foot-pedal speed control device. (electric ones, not pedal-power) How does that work, is it another type of motor?

Wanna know something kinda funny? Long ago, I used to be really into making sure that all turning speeds were mathematically and practically correct, and all was according to established workshop doctrine. Then, one of the lathes belts wore out, and I didn't bother to replace it. I figured that I was confident enough to shoot from the hip and get it right anyway. So now, my lathe has for the last two years only run on two speeds- 350 and 850 rpm. Works fine. Results are way-ok. One for aluminum, one for steel. Brass depends on what mood you're in!

If it is really a sensitive job, I use another lathe. (Lorch)

11-23-2002, 09:56 AM
Yes -- sewing machine motors are typically "universal" motors (with brushes) and their speed control is a totally different proposition. The speed of an induction motor, on the other hand, is locked to the power line frequency. The only way to change the speed of an induction motor is to change the power line frequency...which, in effect, is what a VFD does.

Several places sell surplus VFDs that are actually pretty cheap -- $200 or less, in the sizes you're looking at. By the time you got done screwing around with setting up variable-speed pulleys, I bet you'd be getting close to the cost of a VFD, not to mention the hassle factor.

Take a look at
http://www.dealerselectric.com/ and click on "inverter drives." Also http://www.vfds.com/ to get an idea of what's available. There are other places that others have mentioned.

The Nov/Dec issue of HSM has an article I wrote describing my own expeirences with putting a VFD on my milling machine, which you might find useful. (Unlikely, but anything is possible!)

Oh -- with pulleys, the torque ought to end up the same at the end, no matter what pulley arrangement you put it through, as Peter says.

11-23-2002, 10:28 AM
Torque with belts is solely dependant on slippage of said belts - perhaps a linked polyurethane belt is in your future (A & B widths)?

As to VFD, depending on the quality of the unit & features torque boost is an added bonus feature. It should be noted that continuous torque boost is just stupid - buy a bigger motor if it is a problem. It is normally only used at very low speeds or to accelerate say, a conveyor belt from a dead stop (a common feature required inindustrial applications).

11-23-2002, 02:04 PM
I agree. Don't use the subject name "New Thread". I almost didn't open up this one and now am glad I did. Brother-in-law gave me a treadmill with a worn out track so I ripped it apart and kept the elevator mechanism which was a linear actuator. Don't have a use for it yet. But, now I know what to do with the 1 hp drive motor with VFD. It goes on my lathe!! Thanks.