Speed Control or Countershaft for Flexispeed Lathe?

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.

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.

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.

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.

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

Les.

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.

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

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

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

Regards,

James.

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

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.

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]

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

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.

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

RDG do multi groove pulleys may be suitable

**LINK**

Bob

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.

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

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

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.