Bantam Motor

[Alan .204Participant @alan-204]

[Alan .204Participant @alan-204]

I seam to have lost my book on the Bantam Lathe, problem is the motor's packed up and now I need a new one, it's been using a 240 volt but I would like the replacement to be a three phase running through an inverter, can any one advise me on the HP and RPM the motor should be, the Bantam is the mark 1 1600 any advice would be helpful, the lathe speed would go to 800 RPM but would like to use the full range of speed's up to 1600 RPM.

Regards Alan.

Forgot to say there isn't a data plate on the 240 volt motor that's the reason for the question.

[Martin CottrellParticipant @martincottrell21329]

Hi Alan,

Speak to Pete at Transwave, he's really helpful and I'm sure he will know exactly the motor/inverter combination you need for your Bantam. I have no connection with the company other than as a very satisfied customer. I have recently fitted one of his 3ph motors to my Warco lathe and have to say the transformation has been incredible, quiet, smooth and a real pleasure to use.

Regards Martin.

Edited By Martin Cottrell on 19/11/2014 19:03:53

[Chris GunnParticipant @chrisgunn36534]

The original Bantam motor is a 2 speed motor, 1500 nom rpm in low speed, 3,000 nom rpm in high speed, if your original motor would only take the lathe up to 800rpm, it was probably a 1500 rpm motor, unless the pulleys were changed as well.

Chris Gunn

[Boiler BriParticipant @boilerbri]

I swapped mine for the same size hp in three phase. The frame size was different and I had to drill the mounting plate to suit.

The wiring of the on off and the reverse were also changed to suit. The inventor was fitted in a box withe the isolated and speed pot accessable. It is a worth while change as there is infinite speed control.

Bri

[Alan .204Participant @alan-204]

Thanks Chris for the info, would you know what HP the motor should be.

Alan.

[Bob Brown 1Participant @bobbrown1]

There were two motor sizes a single speed 1hp and a two speed 1 to 2 hp both 3 phase motors.

[Alan .204Participant @alan-204]

I think I have a 3000rpm 3hp motor what do you think, is it over kill.

Al.

[Chris GunnParticipant @chrisgunn36534]

Al, Bob answered the original HP question as far as your 3HP motor, if the motor is the right voltage for an inverter, in my opinion it would not hurt to have some extra power, but do not overdo it and overload the machine when turning, as you could break something. The motor may be "free" but you would need a more expensive inverter to run it.

Chris Gunn

[MuzzerParticipant @muzzer]

3hp 3000rpm sounds pretty sensible. You should still be able to develop similar torque at low speeds to the original in low speed mode as well as being able to develop decent power at high speed. You can make more use of the variable speed and less of the gearbox if you have more power reserve like this. It's handy for varying the speed as you face off a workpiece with power feed, allowing you to keep the surface speed more constant.

With an inverter you can always overspeed it a bit as well, eg for small diameters. A bit of an overspeed isn't going to bother the bearings unduly, as the forces will be fairly light.

3-phase motors are smaller than the equivalent single-phase motors and there's plenty of space at the back of the machine anyway. My 3-phase motor is only something like 1.5 – 2hp and I've managed to bog it down a couple of times, so wish I'd been able to get hold of a larger example when I changed it. I have a 5.5kW inverter, although obviously I have set the limits to suit the actual motor nameplate ratings.

Murray

[Alan .204Participant @alan-204]

Thanks chaps I have a 1HP Inverter with Pendant so I am going to fit a 1HP motor to suit and see how I get on, the motor is 1400 rpm so with the inverter the speed will be easy to reach and for what I do 1hp should be enough, if not the bigger motor will be fitted at a later date and the 1hp motor and pendant will be fitted to the mill as the spindle motor, it cost me £110 for the motor as apposed to over £400 for a pendant and inverter for the 3hp motor, trying to save up to build a new workshop.

Thanks again Alan.

[Chris GunnParticipant @chrisgunn36534]

Alan, that sounds like a plan, my only comment would be to still use the gear box a little, so that you keep the smaller motor running at a good speed, a) to keep the torque up, and b) to keep the motor cool. If one is working at a lower spindle speed. select a lowish gear and fine tune the speed with the inverter.

Chris Gunn

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