Which lathe motor..?

Hi all,

I need a new motor for my small 3 3/4" 'Corbett's' Lathe. the existing motor is a 1/3 HP single phase motor, 4-pole, so 1500rpm (or so).

Before the motor failed, it seemed to run the lathe well, though I did seem to use the higher gears more to get a fast enough speed to get a good finish.

I have access to 1 of 2 potential replacement motors at a good price. One is a 1/3hp 2-pole (3000rpm) unit and the other is a 1/2hp 4-pole (1500rpm).

So neither is a straight like for like replacement.

Would it be better to:

1. Go for the (perhaps over powered for the size of the lathe..?) 1/2hp unit at the same speed as now...?
2. Go for 1/3hp unit at double the current speed, but at the existing power...?
3. neither and continue looking for an exact match for the current motor...?

I'd appreciate your thoughts..

Many thanks in advance

Paul

IMO I would opt for the 1/2HP

You are considering over-speeding your equipment by 100%? Possibly dangerous! No problem if changing the drive pulleys to avoid this, I suppose.

The stronger motor might be a problem with the lathe if attempting to work it too hard, but would be my choice of the two, if they are your only options.

Personally, I would likely go for a 3 phase motor and a VFD, but that does not seem to be an option for you.

I would definitely go for the 1/2hp 1500 rpm option.

A 1500 rpm motor is a 4-pole machine and since power = rpm x torque then the torque will be much higher. That means the lathe isn't going to slow down as much on a big cut. The one thing you need on a machine tool is lots of torque.

Although most of the time the extra torque isn't needed, when do need it is available without running the risk of overloading the motor.

my 2c worth!

The 1/2HP - it's only a modest increase and will give you slightly steadier drive at lower speeds so you don't have to run flat out all the time.

Doubling speed might not be wise with a plain bearing lathe and it could overspeed your faceplate.

Neil

Thanks for you replies - Much appreciated!

You've all confirmed what I had assumed was the best choice - I just had enough of a doubt that I thought it best to ask!

Thanks again

Paul

The 4 pole motor seems to be the most sensible choice for a mill or a lathe, 2 pole motors seem more sensible for where speed takes precident like a grinding wheel or a miniature spindle. I have never tried 6 pole motors. If you want higher speeds using a different pulley/gear ratio can make up the difference and is probably the best way to get a good drive at low speed.

Michael W

PS. I bought a 4 pole B56 framed imperial motor from newton tesla recently and would recommend them, very well constructed. 

Edited By Michael Walters on 12/06/2016 00:19:53