Fitting a Reversing Switch to a Motor on a Myford Lathe

[peak4Participant @peak4]

Posted by Mike Donnerstag 1 on 01/02/2019 16:42:49:

Thanks chaps – I knew I could rely on you all to help me out!

There is an assembly with springs at the back of the spindle, inside the motor. This definitely moves when the motor starts up, so I assume this is the centrifugal switch. Do you think I would still be able to reverse the motor?

Mike

Yes, explained in my previous post.
See the third link.

Disconnect the start winding wires from the paxolin plate, extend them to the input of your reversing toggle switch. Take the wires from the other end of the toggle switch and terminate them where your removed the start winding wires previously.

N.B. Start and stop the lathe with the normal no-volt-release contactor, using the reversing toggle only when the lathe motor is stopped.

 

Bill

Edited By peak4 on 01/02/2019 21:09:39

[duncan webster 1Participant @duncanwebster1]

You can actually get a reversing NVR contactor, my 254S had one before I converted it to 3 phase, if you're interested I could photocopy the wiring diagram from the manual, but if you've already got a reversing NVR and a Dewhurst I'd use them

[Mike DonnerstagParticipant @mikedonnerstag]

Well, I removed all of the wires from the terminals and measured the resistances between each combination. My findings are below:

 

The thick Red and Black wires measure 3.5ohm between them and open circuit to all other wires. I therefore assume these are connected to the run winding.

 

The two Red/Green (striped) wires measure 56ohms between them and open circuit to all other wires. I assume these are connected to the starter winding.

 

The Blue, Yellow and Purple wires measure 0ohms (closed circuit). I'd be very interested if anyone knows where these are wired to.

 

I started by swapping the two Red/Green striped wires over, though this made no difference to the direction of rotation, probably because this is an AC and not a DC motor.

 

I then swapped the Blue and Yellow wires over and, lo and behold, the motor ran in reverse! Hooray!!

I now need some kind of reversing switch, as the lathe didn't come with the original Dewhurst. What do you all think of this one on ebay?:

 

https://www.ebay.co.uk/itm/QS-60-Professional-Drum-Switch-30-A-Forward-Off-Reversing-Motor-Control-TR/132902544459?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D326e5cf24eb04e54a893c05f41c389be%26pid%3D100675%26rk%3D3%26rkt%3D15%26mehot%3Dlo%26sd%3D123613762364%26itm%3D132902544459&_trksid=p2481888.c100675.m4236&_trkparms=pageci%3Ab13ae683-2713-11e9-9629-74dbd180536d%7Cparentrq%3Aaf59a4a31680ad4873ed38e6ffdd39b8%7Ciid%3A1

 

Also, I assume I would need an extra flex with two cores to run between the reversing switch and the motor. How have people done this?

 

Once again, many thanks,
Mike

[not done it yetParticipant @notdoneityet]

No, don’t have two flexes – buy a new flex with the correct number of cores. A far safer option. Proper electrical suppliers will stock a sutable flex – probably not your local hardware store such as Wilco, homebase or similar.

[Martin CargillParticipant @martincargill50290]

A couple of points regarding this.

Whilst its not the best idea to change the reversing switch on a single phase machine capacitor start machine while the lathe is running it won't do any harm because the start winding is switched out (by the centrifugal switch). Any time you change the switch it won't take effect until the motor is started again. N.B, three phase motors are different and reversing the switch will have immediate effect !!!

You can use a simple two pole on/off/on toggle switch as a reversing switch. You wire a pair of crossover wires between the two end pairs of contacts and then feed live and neutral to the middle pair. The feed to the capacitor and start winding goes onto either of the pairs of end contacts. Switching the switch from one end to the other will reverse the motor.

My own lathe does not have centrifugal switch built into the motor, instead it is supposed to use an external current sensing relay to switch out the start winding once the current drawn by the winding allows. Not having this fancy relay (they are still available but they seem to be used/available only in the U.S.A,) Instead I have an extra set of contacts on the back of the start button that power the start winding. Pushing the start button for a second or so holds the start winding energised during start up, once you release the button the start winding drops out leaving the main winding held on via the NVR contactor

Martin

[duncan webster 1Participant @duncanwebster1]

Posted by Martin Cargill on 02/02/2019 19:45:36:

A couple of points regarding this.

Whilst its not the best idea to change the reversing switch on a single phase machine capacitor start machine while the lathe is running it won't do any harm because the start winding is switched out (by the centrifugal switch). Any time you change the switch it won't take effect until the motor is started again. N.B, three phase motors are different and reversing the switch will have immediate effect !!!

You can use a simple two pole on/off/on toggle switch as a reversing switch. You wire a pair of crossover wires between the two end pairs of contacts and then feed live and neutral to the middle pair. The feed to the capacitor and start winding goes onto either of the pairs of end contacts. Switching the switch from one end to the other will reverse the motor.

My own lathe does not have centrifugal switch built into the motor, instead it is supposed to use an external current sensing relay to switch out the start winding once the current drawn by the winding allows. Not having this fancy relay (they are still available but they seem to be used/available only in the U.S.A,) Instead I have an extra set of contacts on the back of the start button that power the start winding. Pushing the start button for a second or so holds the start winding energised during start up, once you release the button the start winding drops out leaving the main winding held on via the NVR contactor

Martin

That's pretty much what I did when the centrifugal switch died on a very old motor I had on my ML7. It was so old that in the 1990s there was no-one at the makers (Crompton Parkinson) who was working there when it was made. Despite this they sent me some capacitors to reduce the start current and a diagram of how to connect it as Martin has. Worked a treat, just need to use some intelligence, hold down the start button till it's got going. You don't get that sort of after sales from Banggood

[AJWParticipant @ajw]

The fans on both of my VFD’s are able to be powered on all the time the controller has an output or able to be switched by an onboard thermostat.
This function is configured in the setup.
I have them only using the fans when required – rarely, so they are silent in use.

Alan

[john fletcher 1Participant @johnfletcher1]

Pleased to hear you have the motor sorted Mike. Martin those current sensing relays are fitted to most Fridges and I'm sure with a bit of Model Engineering ingenuity one could be adapted. They have three external Lucar type terminals and three internal in which three pins on the outside of the motor/compressor fit in a triangular formation, the top pin is the common.

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