Options for Variable speed drive on Atlas 12" lathe ?

I have a 12" Atlas 3900 series and it came with a large Hoover 1 pH, 1 hp, 1420 rpm motor, what are my options for a variable speed drive on this machine?

The motor will be mounted underneath. I don't have space in my workshop for the countershaft arrangement.

Rich

Have a look on Lathes UK site, it looks like you have a choice of 16 spindle speeds covering an excellent range.

To get variable speed means a new 3 phase motor and a VFD to control it.

Emgee

Edited By Emgee on 24/07/2022 15:03:22

I assume you are intending to get an new 3 phase motor.

As I want to avoid a counter shaft on my (very slowly progressing) lathe rebuild I went for a 6 pole 3 phase motor. This gives a 50Hz speed of only 910 /1000 RPM and has very little torque ripple. Not as common as 2 and 4 pole though. Coupled with a qualty vector mode VFD (I got a Toshiba) I think this will work well.
The 1/2 HP motor I got was a bargain but is a bit small for your Atlas. It has everthing I want for the ML2 though. Inverter rated, totaly enclosed etc.
www.ebay.co.uk/itm/324955281773

Edit, Had a look and this looks like it might do your job
https://www.ebay.co.uk/itm/232778108037

NAWTS

Robert G8RPI.

Edited By Robert Atkinson 2 on 24/07/2022 15:21:28

+1 for Roberts suggestion of a 6 pole motor rather than the usual 4 pole. Generally not that much more expensive is our sort of sizes.

The lower base speed of the 6 pole motor means torque and power hold up much better when speed is reduced using a VFD.

For practical purposes the "don't see a significant difference in motor performance" range of a modern motor running from a modern vector drive VFD is ± 1/3 rd the nominal speed. So a 6 pole motor runs up to pretty much same speed as the original with no practical difference in performance and goes down to around half the original speed before you seriously have to start engineering for the lower power.

Obviously you don't get the torque multiplication of changing to a lower gear or belt pulley step ratio but if you choose your normal operating gear or pulley step wisely the VFD and back gear can handle the most of your desired speed range without the motor running out of oomph.

I'd probably reduce the primary drive ratio a bit to further enhance the useful low speed range. High speeds are for smaller jobs so you don't need that much power anyway. It's pretty rare that my S&B 1024 goes over 1,000 rpm let alone makes it to the 2,200 top end!

Using a 4 pole 1,400 rpm motor tends to waste the higher speed capabilities of the VFD.

Clive

Ive just put a 3 phase motor on my lathe. Everything came from Newton Tesla. Maybe they can help you.

Can the original counter shaft arrangement be mounted underneath?

Hi Rich2502, you can have the countershaft wherever you like as long as the belt will allow. My Boxford underdrive has the countershaft in the cabinet directly below the lathe, but of course the lathe and cabinet was designed that way.

Regards Nick.