Newbie needs advice about a lathe

[Steamchick]

Thanks Baron, VERY USEFUL. Must check, but I suspect my controller is limited to 5A continuous rating... but off-hand, I think it is the same size body as my 750W rated lathe motor. - To get the extra 330W it must have better magnets, better cooling (I can see the bigger fan!), and better armature windings (Thicker wire?) - and is possibly longer internally?
A nominal 40% increase in torque, as it is rated at the same speed as my lathe motor. Perhaps I shall buy one and see? But if I have to limit the volts, in order to stay within aa safe max working current for the controller, then I may lose all the benefits of the 40% extra torque, so need to do my homework on the controller now.
Thanks,
K2

 

[BaronJ]

Thanks Baron, VERY USEFUL. Must check, but I suspect my controller is limited to 5A continuous rating... but off-hand, I think it is the same size body as my 750W rated lathe motor. - To get the extra 330W it must have better magnets, better cooling (I can see the bigger fan!), and better armature windings (Thicker wire?) - and is possibly longer internally?
A nominal 40% increase in torque, as it is rated at the same speed as my lathe motor. Perhaps I shall buy one and see? But if I have to limit the volts, in order to stay within a safe max working current for the controller, then I may lose all the benefits of the 40% extra torque, so need to do my homework on the controller now.

Thanks,
K2

Hi K2,

If your machine has the Kbic controller like my mill then the sense resistor would need changing to allow higher power motors to be usefully used. As I've just discovered on my mill ! Which also explains why the power drawn from the mains is very little changed.

FWIW, I get my treadmill motors from the local scrap yard usually for a fiver, with the option to take it back should it prove faulty ! So far I haven't had one.

 

[Steamchick]

Thanks for the advice! Very useful. I'll see what I can buy for scrap value!
K2

 

[hanermo3]

I tried a DC treadmill motor on my 12x lathe with a gecko 320 servo and encoder.
And a 180 V DC motor driven at 48 V.
This was a bad idea.
It sparked, smelled, overheated, while working.

The original motor is industrial 1.5 kW continous AC 220V single phase.
With belt drive and backgear.

I now have a 2.5 kW AC brushless servo, driven via 1:3 30 mm wide HTD-8 belts.
This is fantastic !

I get about 90 Nm peak torque, very much more than the original, and not belt changes ever, and c axis, and 0-1000 rpm via industrial pots on the control panel.
And "perfect" speeds for css and excellent finishes.

I never knew lathes really want much more torque.

 

[Bentwings]

Cutting 4130 and 5140 takes even more . Make sure skids are in perfect order or you will get chatter as it is the cutting forces may actuator deflecvthe chassis make sure your tools are securely mounted an not sticking out too far cast iron can be tough too especially raw un machined castings just make everything well secured interrupted cuts will hammer everything .

 

[william_b_noble]

FWIW, I have a 12 inch lathe, it has a reeves drive and dual drive belts from a 2 HP 3 phase motor to the reeves drive. the belt will slip in back gear when tapping 1 1/4 or 1 1/2 inch holes, depending on the particular steel I end up using. at the other end, when I am reducing the diameter with heavy cuts, the VFD fan goes into full speed mode - in both cases that's an indication of the need for more torque and more torque will need more HP.

running a DC motor on 1/4 voltage (approx 180 to 48) gives you 1/8 of the HP, and the sparking is telling you that the motor was greatly overloaded. Destroying a good motor by operating it outside of its specifications can be a learning experience -

 

[BaronJ]

I tried a DC treadmill motor on my 12x lathe with a gecko 320 servo and encoder.
And a 180 V DC motor driven at 48 V.
This was a bad idea.
It sparked, smelled, overheated, while working.

The original motor is industrial 1.5 kW continous AC 220V single phase.
With belt drive and backgear.

I now have a 2.5 kW AC brushless servo, driven via 1:3 30 mm wide HTD-8 belts.
This is fantastic !

I get about 90 Nm peak torque, very much more than the original, and not belt changes ever, and c axis, and 0-1000 rpm via industrial pots on the control panel.
And "perfect" speeds for css and excellent finishes.

I never knew lathes really want much more torque.

I tried a DC treadmill motor on my 12x lathe with a gecko 320 servo and encoder.
And a 180 V DC motor driven at 48 V.
This was a bad idea.
It sparked, smelled, overheated, while working.

I'm not surprised, at 48 volts it wouldn't be rotating fast enough to utilise the fan assuming that there is one. Also some of these motors are designed to only spin in one direction.

A note to K2.
I changed the current sense resistor to a 0.02 ohm 10 watt one ! It made little or no difference to the supply current with the motor at full speed no load. Which I suppose is to be expected. At the moment the mill is set up for a turning job, so the load is quite light.

 

[william_b_noble]

note, if you are using a DC motor that the motor's top speed ocurrs when the back EMF is equal to the applied voltage (this is for an ideal motor with no friction or losses, a real motor will be close but not quite equal).