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single or 3 phase ?

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Gary Maynard23/02/2018 10:42:42
8 forum posts
5 photos

Hi real newbie question I have a Raglan mk2 lathe and in the process of setting it up in my workshop, It has a 3ph motor and i already had a single phase to 3 phase converter but as its a 440v motor this will mean running it at 2/3 the speed . Do you think this is an issue or should i go the single phase motor route to get maximum speed ? I have read that 3ph motors produce a better cut i that true ?

The only lathes I have experience of have been 3ph

Neil Wyatt23/02/2018 19:32:06
13410 forum posts
576 photos
68 articles

Hello Gary,

Yes 3-phase gives smoother power than 1-phase and many people report a better finish with 3-phase.

Using a converter shouldn't affect the speed of the motor.

If the converter is powerful enough for the motor, what you need to do is rewire the motor from star to delta. Most 3-phase motors make this easy by having moveable links in the wiring box, often with a diagram of how they should be moved.

Can you post photos of the motor's rating plate and inside its terminal box?


Jon23/02/2018 20:59:53
774 forum posts
42 photos

Presume mean rotary convertor that run at least 3ph 400V from 1ph 240v input, will do the job no mods if its big enough.

Have a 5.5kw its not man enough for my 2.25kw via gearbox not to mention the noise.

Geared head will show up more with 1ph, last lathe looked like chaff marks as the motor pulses think its twice per rev. 3ph 4 pulses per rev, some one correct me but definately shows up.

Martin Connelly23/02/2018 22:31:15
623 forum posts
67 photos

The lower voltage will not result in a 3 phase motor running slower but with lower power. This will cause it to slow if it is loaded but unloaded speed is set by supply frequency. This is why variable frequency drives are used for speed control.

Search for star and delta motor connections, you may be able to change the motor to 240V.

Martin C

not done it yet24/02/2018 00:56:07
1800 forum posts
11 photos

As it should only be a 1/2 horse motor, a 415V inverter, from single phase 220V supply, is not that expensive. I fitted one to mine and was very pleased with it. Likely the extea cost would not be more than paying for the star to be split.

I mostly used the usual vario-belt for speed setting, but the soft start feature was a good asset, among others. The top speed sometimes being a bit on the slow side, at around 1700rpm can be upped considerably. Raglan did offer a 2800rpm version, so the spindle bearings were perfecty OK for extra speed, if necessary.

If you need a more reproducible spindle speed, a rpm counter is only around a tenner from epay. Not particularly necessary, but easily fitted if wanted.

Edited By not done it yet on 24/02/2018 00:56:37

Russell Eberhardt24/02/2018 10:48:36
2216 forum posts
79 photos

If the motor can't be changed to star configuration I would buy a new motor. They are cheap enough: **LINK**

Probably cheaper than other options.


not done it yet24/02/2018 11:04:20
1800 forum posts
11 photos

Yes, but one must know which foot to get for fitting to this lathe - not all are suitable as the vario-speed system requires some quite specific geometry to work.

I would add (to my previous post) that, if an inverter were to be fitted, a 220V three phase item would be more useful if needed to be installed elsewhere at some future date...

Martin Dowing24/02/2018 17:58:34
245 forum posts
4 photos

I would hold to 3 phase system with hands and legs.

Anything what 1 phase motor can do 3 phase motor will do better.

And if you can connect your motor in star or delta configuration, it will also allow for generous degree of speed control. You may fiddle with frequency and voltage to get speeds even higher than nominal without loss of torque. You don't need to be an electronic geek either to get there as adequate "in box" circuitry is commercially available.

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