Variable rpm control for watchmakers lathe

Is there a variable rpm speed controller, that can be used to control watchmakers lathe ac motor, that uses a knob instead of a foot pedal?

I expect you don’t actually need one, per se. Simply replace the foot pedal with a suitable rotary potentiometer?

Edited By not done it yet on 19/03/2021 06:50:23

I have just taken a foot controller of a sewing machine to pieces. Basically, its a pile of 1/2" diameter discs (carbon like) stacked on top of each other contained by a sturdy ceramic block. When the discs have no pressure on them, no current flows through the pile. Increasing the pressure on the pile increases the speed of the AC motor (This is intuitively wrong ?). This arrangement could be converted to a knob type basis I suppose.

.

The once-very-popular ‘Drill Speed Controller’ should do the job nicely ... early versions used SCR devices and were only half wave, but the later ones used Triacs and ‘zero crossing point’ circuitry: These should give smooth and interference-free control.

If you want to build one: There should be plenty of designs available.

MichaelG.

.

A very quick Google search : http://www.google.co.uk/search?q=triac+drill+speed+controller+schematic

Edited By Michael Gilligan on 19/03/2021 07:42:37

Henry, when you say ac motor, what type? Does it have brushes?

+1. The answer the Henry's question is almost certainly yes, but the type of controller needed depends on the sort of AC motor fitted. Most likely it's a Universal with a rheostat foot pedal as fitted to older sewing machines, but it may not be.

Any information on the motor plate? A picture of the motor and the foot-pedal might identify it. Brushes are a good clue!

Dave

.

Mea Culpa ... I assumed it to be the classic ‘Sewing Machine Motor’ implementation.

MichaelG.

Aha! The ever rare 'Zambesi Pile' - an early form of variable resistor. Used in large form for a high amperage battery test system. I've got one of these buried in my shed which is capable of loading a 500 amp car battery to test the plate condition. Glows red and sparks inside when you 'load' the battery with the big screw on the front of it. Must admit I had never realised sewing machine motors were controlled by these but can see the potential.

Martin

I have a VFD and induction motor on my watchmakers lathe. The control box has speed pot and jog functions, plus reverse. I called Newton Tesla and spoke to them - they put together a set - watchmakers lathes requirements being a bit different to a larger bench lathe.

Dave

In September 1980 issue of ETI magazine there was an article on an electronic speed controller for an electric drill using a Triac. I think this would do the job for you. As ETI is no longer with us, I think I will be OK sending you a copy, as an attachment to an email. Please send me a PM with your email address. John

John Fletcher, pm sent...please.

My watchmakers lathe is driven by a simple sewing machine "universal" motor.

I implemented a speed controller to replace the crude foot switch (3 speeds and off*) using a standard 400W lighting dimmer switch. It was very cheap from fleabay and works fine.

* The three speeds were full power, half wave rectified and half wave rectified with series resistor. The pedal applied power then  shorted out (in sequence) the resistor then the diode.

Edited By Peter Cook 6 on 19/03/2021 13:13:30

If a universal(brush type) motor then a speed controller from an old vacuum cleaner will work or as said by Peter a 3 0r 4 hundred watt light controller will work and very cheap. Noel.