Lathe Motor

John_S · 14 Nov 2017

Hi, I'm new to diynot, but not new to diy; this is my first post so please forgive me if I say too little or too much.
I'm trying to restore to working order a mid-1900s wood lathe - good quality and in overall good condition, and one particular problem is the motor. It's non-standard but I don't want to change it unless I have to because it seems in fine condition and fits the bracket on the lathe. It's 1hp single phase 230V AC capacitor start, and although it has a 3-pulley block it runs too fast at 2850rpm rather than preferred 1425rpm.
Is there any practical way to reduce the speed electrically rather than try to find a mechanical reduction system? A friend said try a Variable Frequency Drive but I want to get a second opinion before I start spending money on a solution that might not work.
Thanks for reading this.

Jackrae · 14 Nov 2017

Basically there's no "decent" method of reducing the speed of a 1Ph capacitor start motor as it will have a centrifugal switch installed to switch out the capacitor once the motor is up to speed and so must run fast enough to operate this switch. VFDs are excellent but for that you'll need a 3-phase motor with a winding suitable for 230v phase to phase. Your choices are, change motor for 1425 version, install different pulleys, install lay shaft to build in multi belt pulley system or change to a 3-phase motor via a VFD. Note that "domestic" 3-phase output VFD units designed for operation with a 1-phase supply are readily available.

stillp · 14 Nov 2017

Unlikely that a VFD will help - they are a good solution for 3-phase motors, but won't work with a capacitor start single phase. How many poles is your motor? (How many terminals are in the terminal box)

John_S · 17 Nov 2017

Thanks for the information so far. Beginning to look like I'll need to get a 3ph motor and fresh bracket made. But to answer stillp's question, there are 4 terminals on the motor (excluding earth which is straight to the casing). Does that get us any further?

Jackrae · 17 Nov 2017

Probably not. A photo of the terminations would have helped with a definitive answer, but this link shows a typical 4-terminal motor connection.
http://www.instructables.com/id/Wiring-up-a-Brooke-Crompton-single-phase-lathe-mot/

stillp · 18 Nov 2017

John_S said:
Thanks for the information so far. Beginning to look like I'll need to get a 3ph motor and fresh bracket made. But to answer stillp's question, there are 4 terminals on the motor (excluding earth which is straight to the casing). Does that get us any further?

It does, but not in the way you want - it confirms that you cannot change the speed of that motor.

conny · 18 Nov 2017

Your motor is a 2 pole and you want a 4 pole. There is no way to convert it. You will have to buy a 4 pole or use reduction gearing.

John_S · 29 Nov 2017

Thank you all for comments & suggestions. I'm working on the results now but it'll doubtless be after Christmas before any useful progress is made.

Taylortwocities · 30 Nov 2017

John_S said:
it'll doubtless be after Christmas before any useful progress is made.

Wow, that's one heck of a party that you are going to. Can we all come?

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Lathe Motor

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