Speed Control or Countershaft for Flexispeed Lathe?

[James AlfordParticipant @jamesalford67616]

The motor for my Flexispeed arrived yesterday and looks good. I now need to set it up on the machine and am not sure which would be better to use to reduce the speed: a PCW speed controller or a countershaft. The motor speed is 1,350 RPM.

I seem to recall somewhere that using a countershaft is more effective at reducing chatter than a direct drive, but am not sure whether this is the case.

I would appreciate ideas.

Thank you.

James.

[James AlfordParticipant @jamesalford67616]

[Les Jones 1Participant @lesjones1]

Hi James,
First. What kind of motor is it ? Single phase / 3 phase induction motor. Series (Universal.) , shunt or permenant magnet ? I do not know what a PCW speed controller is. Do you mean a PWM (Pulse width modulator.) speed controller ? Even with a speed controller I think it is a good idea to have a few belt ratios to give you more torque at lower speeds. (Unless the lathe has backgear.)

Les.

[James AlfordParticipant @jamesalford67616]

Les,

Thank you.

It is a single phase capacitor run motor (not sure about induction or other). I did mean PWM and the lathe has a back gear.

Regards,

James.

[Michael GilliganParticipant @michaelgilligan61133]

James,

As I'm sure Les will be able to explain in detail … that type of motor does not lend itself to electronic speed control.

I would definitely go for mechanical speed reduction … preferably using Poly-V pulleys and belts.

[there have been several threads on the forum, discussing the merits of these]

MichaelG.

[Les Jones 1Participant @lesjones1]

Hi James,
I agree with Michael's comments. A capacitor run motor is a form of induction motor.

Les.

[James AlfordParticipant @jamesalford67616]

Thank you for the advice. I take it then that induction motors do not like speed controllers.

Is there any advantage in a countershaft other than offering more ratios than direct drive?

[Les Jones 1Participant @lesjones1]

Hi James,
Single phase induction motors would require a very complex design of speed controller. As well as a variable frequency supply (Which is quite easy to achieve.) they would need some way of providing a phase shift to the auxiliary winding. With a fixed frequency the capacitor does this but as the frequency is changed the value of capacitor would need to be changed. A 3 phase induction motor is relatively easy to change its speed by changing the frequency and amplitude of its power supply. This is why changing from a single phase motor to a 3 phase plus a VFD is so popular.

Les.

[Roderick JenkinsParticipant @roderickjenkins93242]

The big advantage of the countershaft is that the full torque of the motor is always available throughout the speed range. There are some very sophisticated variable speed systems available for various other types of motors but, while they are very convenient, none of them provide the full torque (and therefore power) of the motor at the lower speeds.

Rod

[Roderick JenkinsParticipant @roderickjenkins93242]

What I should have said was that the stepped pulleys from the countershaft to the lathe spindle give you the speed variation. The motor to countershaft pulley ratio brings the countershaft speed down to a suitable value for the lathe whilst still retaining the full torque/power available from the motor. If you had a motor running at 500 rpm then you wouldn't need a countershaft.

Rod

[James AlfordParticipant @jamesalford67616]

Thank you for all of the replies. I'd best go and find some pulleys and make up a countershaft.

Regards,

James.

[WorkshopPeteParticipant @workshoppete]

Hi All

Is 1350 RPM for an induction motor not odd should it be either 950 or 1675 rpm for 50 hz? ( see James first post).

Regards

Peter

[Les Jones 1Participant @lesjones1]

Hi Peter,
I don't know haw you have calculated the speed for a 50hZ 4 pole motor. Your value of 950 RPM is about right for a 6 pole motor. The synchronous speeds for 4 pole and 6 pole motors would be 1500 and 1000 RPM (50 x 60 = 3000 3000/2 = 1500, 3000/3 =1000) There always has to be some slip so current flows in the rotor bars so the actual speed is always a bit less than synchronous speed. I agree that 1350 rpm does seem a bit low (I would expect 1400 – 1450 rpm.)

Les.

[Michael GilliganParticipant @michaelgilligan61133]

For info.

On 10-Jan-2015, in his previous thread, James kindly posted the ebay link to the motor that he was buying.

MichaelG.

.

Edit: [quoted]

Michael,   Here it is as an actual link.   **LINK** Regards, James.

 

Edited By Michael Gilligan on 17/01/2015 08:52:47

[James AlfordParticipant @jamesalford67616]

Posted by Peter Newby on 17/01/2015 08:16:48:

Hi All

Is 1350 RPM for an induction motor not odd should it be either 950 or 1675 rpm for 50 hz? ( see James first post).

Regards

Peter

I have just checked the motor and realsied that the correct listed speed is 1,370 RPM, not 1,350 as I originally stated. Sorry for any confusion.

Regards,

James.

[Ian S CParticipant @iansc]

A motor that size would usually be a shaded pole type, and probably inefficient enough to run at 1350rpm. Two shaded pole motors that I have, including the one that drives my Super Adept lathe require a capacitor to run.

Ian S C

[Bob Brown 1Participant @bobbrown1]

RDG do multi groove pulleys may be suitable

**LINK**

Bob

[Michael GilliganParticipant @michaelgilligan61133]

James,

You mentioned, on your other thread, that the lathe was a Flexispeed Meteor II

If you haven't already done so; the lathes.co.uk page is a very good place to start.

… and perhaps create an Album here, with some photos of yours for us to see.

MichaelG.

[WorkshopPeteParticipant @workshoppete]

Sorry Les

Yes of course you are right Having worked on both sides of the pond I was getting 50hz and 60hz speeds mixed up but still 1370 seems very slow.

Regards

Peter

[oldveloParticipant @oldvelo]

Hi James

Can I add a little more info on "Chatter"

"I seem to recall somewhere that using a counter shaft is more effective at reducing chatter than a direct drive, but am not sure whether this is the case"

Here is a link to a query I posted on another forum why my lathe with a 180 volt DC motor with speed control ran so much smoother than the original AC motor. May be of interest to you and others following this thread.

http://www.homemodelenginemachinist.com/showthread.php?t=17383

Thanks to Ken for the full explanation of why this is so.

Have you considered a DC drive and speed control. Personally I think they are Ideal for the home workshop machine tools.

Eric

[James AlfordParticipant @jamesalford67616]

Thank you all for the extremely helpful and detailed replies.

Bob: thank you for the link to RDG which I shall look at.

Michael: thank you for the link to lathes.co.uk which, as you say,is very good and helped me to clarify the spindle thread. I can now keep a better eye out for any 1/2" BSF faceplates or chucks…………

Eric: I shall read you link about chatter. I did consider DC rather than AC and pulleys, but the DC things that I found looked very expensive, unless I was looking at the wrong type of thing.

I am happy to create an album on the lathe once I have cleared the garage enough to find my work bench again. I currently contains large amounts of my son's BMW E30 which he is rebuilding and a pile of kitchen bits from work in the house.

Regards,

James.

[James AlfordParticipant @jamesalford67616]

For a variety of reasons, mainly being busy rebuilding the kitchen and now the workshop, I have yet to set up this lathe. I have been looking for a set of suitable pulleys to make up a countershaft, but still like the idea of electronic control if affordable and practicable.

I have seen these on E-bay and wonder whether anyone can suggest whether either would be suitable for a single phase, capacitor start AC motor of 120 watts?

**LINK**

or

**LINK**

Thank you.

James.

[Les Jones 1Participant @lesjones1]

Hi James,
The simple aswer is no and no. Single phase induction motors are not suitable for speed control. I did see a design in the "Elektor" magazine once that claimed to work but I would not reccomend it. The solution is a 3 phase motor with a VFD or a permanent magnet or shunt DC motor with a suitable PWM speed controller or brushless DC motor with a suitable speed controller.

Les.

[Ian S CParticipant @iansc]

When you make up a counter shaft, as well as the 3 pulleys to the lathe, it's worth while putting a 2 or 3 speed pulley from the motor to the counter shaft, that along with the back gear gives you 12 speeds, and if you work it right, your low speed could be 30 rpm or less, just don't go for excess speed at the top end. Use HSS tools, be prepared to run a bit slower, and the wee lathe will work to the maximum it can handle.

Ian S C

[James AlfordParticipant @jamesalford67616]

Thank you both for your replies.

Les: that is pretty much what I had expected, but it was worth checking, especially at the low price of the two controllers.

Ian: a good idea about the additional speeds. I shall see what I can find in the way of pulleys.

Regards,

James.

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