Making a lathe variable speed?

Question

I have a bench lathe where the speed is adjusted by moving belts on different sized pulleys. As this requires stopping the lathe and opening the access panel, I would like to be able to change the speed on the fly. I have seen variable speed control boxes that you plug a tool into then dial the speed up and down. They all state that they are not for use with slow start motors. How do I know if the motor I have is slow start? Does anyone have any other suggestions?

Answer 1

Since your MOTOR isn't gear drive, but belt drive, it seems to me it was manufactured at its highest level of strength, to support the various alterations via the belts. I have to assume it's an older model.

I'm not an electrician but I've used many lathes, often.

I suspect that a "Rheostat" would only put more strain on a motor not designed in that technology. I'll also assume that most or all lathes aren't instantly at 25,000 plus RPM's, as Routers aren't strictly either. To recreate a slow start motor is better left to those more qualified, or who understand the design and dynamics of the motor.

Steven Wolf
(The Rev.)

Answer 2

It sounds to me that it is a slow-start motor. Merely because it is belt driven. However, you would know best! Does it start slow. That is really what a slow-start motor is. Does it take a a little bit to achieve its full speed/rotation? Or, does it go to an instant on? My lathe is quick start, but when I was a kid, we had a slow-start. You can use a variable speed control box with it even if it is a slow-start, but you will wear out the motor (brushes) fairly quickly. Why, you ask? The motor is not designed to run at a variable speeds and what you would be doing is slowing it down - in turn causing the motor (brushes) to overheat. Belt drives run at one speed and the various belts determine the speed - as you already know! However, quick start motors are made to run hot and it would less of a strain on the motor. Lathes can be fairly cheap to purchase these days and they will last as long as the way you use it. Check on the web and find wharehouse tool distributors. I bought one 2 years ago for $90 and it still works just fine! If you decide to use a variable speed control box, be concerned of overheating or a fire.
Good Luck to you!

Answer 3

Without getting into the electronics, most lathes with variable speed are DC voltage motors and use a rheostat to control the speed of the lathe. You have to use a transformer to change AC voltage to DC voltage and use a motor large enough to do what your lathe is designed to do. It can be expensive.

Answer 4

I don't quite agree that using a variable control alone heats up the brushes and the motor. What is happening is that AC speed controls work on the principle of chopping part of the AC's sine wave off. As a result, the motor slows down but also and more importantly, loses mechanical power. You, using your cutting tools on the work piece, cause a mechanical strain on the motor which "he" can no longer deliver, and therefore heats up.

Any solution that really works, be it electronically or a mechanical gear box, is likely so expensive that you rather continue to swap your belt positions.

Answer 5

first off, dont stick a light dimmer on there....seen that one to many times...

you can control the speed of an AC motor but its not good for it and DC motor controls are much more precice.

you should upgrade the lathe or just stick with the belt changes.

yea its not fun as its how my drill press is set up but it works...

Answer 6

My suggestion is you could use a frequency inverter.this changes the speed of your A.C.motor by controlling the hertz.normal American power is 60 Hz.and can be taken up to 180Hz.or down to10Hz. depending on motor load.This is not a difficult install but could be expensive..This will work with slow start motors as you may change the ramp up or ramp down speed to meet your needs

Answer 7

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