[serriadh]

I've somewhat unexpectedly come into posession of a mysterious old 7x20ish lathe which I belive to be an "RandA Model A Long Bed", judging by a trawl through lathes.co.uk which gave me a bunch of images here.

It seems to at least be in working condition... I've had a quick fiddle using a dial test indicator and it would appear that runout is minimal and that the ways are flat, though I'm not certain how much to trust the indicator yet as it isn't brand new and I've no idea how you might go about testing one

It isn't perfect, and I've come across a few issues. Looks like the previous user managed to crash the carriage whilst driving it under power with the leadscrew. The half-nut mechanism is a bit warped, and I'll probably need to replace a couple of bits there. There's a long slot on the tailstock spindle... the idea being there's a little pin that engages with it to stop the spindle turning when you want to move it in and out by rotating the tailstock handwheel. The pin is missing, and the bit of the tailstock casting that held it appears to have been smashed off. Also not too hard to fix.

Lastly, there's a motor provided but no speed control circuitry or anything. I've not even any idea if it is AC or DC. Moreover, there's only a single belt joining the motor sheave to the headstock pulleys, no countershaft or anything. This suggests to me that the headstock spindle is going to be turning far too fast to be very useful.

The first thing I'd like to do once I've cleaned up the lathe and re-oiled it is to use a motor I actually know something about with a decent speed control and see if everything runs smoothly, and this is the thing I'd like to pick your brains about first and foremost.

It seems that the recommended motor power for a small lathe is half a horsepower or so. Now, what I want to know is why. Is it because larger motors generate too much torque? I'm looking at a high-torque, low-rpm induction motor like ths one which I can control with a little vector drive. Though the power output is low, the torque is quite high. Now if having too much torque is a problem, should I be avoiding this sort of motor?

[colin gibson]

0.37kW is a normal size for a small lathe. Torque at the motor is not so important as long as the transmission ratios are in range. The torque at the lathe spindle is what is most important, this changes to capability to apply pressure on the tool at the various diameters and feed rates you apply to the work.

We created a calculator for this - See...
http://www.inverterdrive.com/lathe-drive-select.aspx

Let me know if this is understandable and useful?

Regards - Colin
www.inverterdrive.com