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motor wiring

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Wokauk29/08/2012 20:51:31
17 forum posts
3 photos

The wiring on my Myford ML7 consists of a household plug, when you plug it the motor turns. It isn't even earthed. The motor has 4 terminals and no obvious capacitors.

Three swiches came with the lathe which are not connected. A start, a stop and lockable forward reverse.


A few questions,

1) Should the motor have a capacitor, if so what specification?

2) The stop and start switches are momentary switches, so to use I would need a contactor of some description. Any advise over which contactor to get?

3) Should I junk that idea and get a Dewhurst switch?

4) Is running the lathe in reverse useful?



NJH29/08/2012 21:08:59
2314 forum posts
139 photos

1 Don't run without an earth - a wiring fault could prove FATAL

2 Buy a NVR switch with push buttonn ON/OFF. This one is OK and has the advantage of a big OFF button in case of sudden disasters! This switch disconnects the mains feed if the power fails. Without this, in event of a power cut, the motor will restart when the mains is restored. (You could have your hand in there when that happens.)

3 A Dewhurst switch is included in the motor wiring to allow forward and reverse running. You will still need the NVR as the Dewhurst is not designed to break the circuit and , in time, the terminals will burn out if you do so.

4 I don't find it necessary to run my lathe in reverse. There is the problem too, with screw on chucks like on the Myford, that cutting with the lathe running backwards could unscrew the chuck.

Hope that helps a bit



Edited By NJH on 29/08/2012 21:11:09

Edited By NJH on 29/08/2012 21:14:09

Edited By NJH on 29/08/2012 21:14:45

Clive Foster29/08/2012 22:32:31
3135 forum posts
109 photos

No capacitors needed with that motor, it has a simple start winding. Lower starting and run-up torque than the capacitor start versions but I can't see that mattering on a lathe where you are only spinning up the spindle, chuck etc not trying to drive up against a load.

The NVR Norman suggests is effective and good value for money. Easy to wire as well. Not as durable as a proper industrial rated contactor but I've used similar budget range devices for over a decade when fixing things for other people and have yet to have one come back.

If you decide to use your switches and buy a contactor, any of the lower end industrial devices from RS components et al will be just fine. But do buy a DIN rail mount and a short section of rail. Fitting is sooo much easier compared to the usual "screws carefully placed so you can't quite get on them" set-ups.

Like Norman I'd not want to run in reverse with a screw-on chuck but if you do decide to use a contactor and the lockable forward / reverse switch its best to get the official Brook connections. I have a PDF of the Brook Gryphon sheet covering the full small motor range somewhere if you want it.


Russell Eberhardt30/08/2012 13:51:30
2737 forum posts
86 photos

I do find reverse useful but only for unscrewing the die when making a long thread or removing a stuck chuck from the spindle with it in low backgear speed.


DMB30/08/2012 16:42:59
1312 forum posts
1 photos


Not sure about running lathe in BG to un-jam a chuck. Sounds like a recipe for stripped gear teeth. A Myford with conjunctivitus? not good!

My S7 has a locking pin on the left hand side. I would use that and key in chuck.


Russell Eberhardt31/08/2012 21:12:38
2737 forum posts
86 photos

On my Atlas lathe the locking pin is more fragile than the back gears, although of course it would be cheaper to replace!


John C31/08/2012 21:21:09
273 forum posts
95 photos

Running in reverse is very useful for single point cutting metric threads - but only to move the tool back to the start, no cutting force applied.


Wokauk09/09/2012 22:11:19
17 forum posts
3 photos

Thanks for all the advice and information.

I wired up my motor to my push buttons using a contactor and found that when put into reverse it blows the fuse. I don't think I have wired up the button or the motor incorrectly (however not imune to cocking it up).

Having found nothing wrong with my wiring I tried the following, direct from the mains to the motor.

Live to bridged A1/Z1 neutral to bridged A2/Z2 = motor spins clockwize

Live to bridged A1/Z2 neutral to brided A2/Z1 = fuze blows, I would expect anti clockwize rotation if all well?

I measured the the resistace across the terminals,

Z1 to Z2 is 3.6 ohm

A1 to A2 is 3.8 ohm

Z1 to A1 is 0.3 ohm

Z2 to A2 is 0.3 ohm

I am happy to use the motor in forwards only, sounds like I don't need reverse but is the motor running with reduced power.?

Thanks again,











Edited By Wokauk on 09/09/2012 22:12:18

Les Jones 109/09/2012 23:00:20
2257 forum posts
156 photos

Hi Wokauk,
I think A1 is bridged to Z1 and A2 is bridged to Z2 internally. Without your bridging wires or any connection to the mains there should be no continuity between the A terminals and the Z teminals if you want to reverse the motor. If there is no internal connection between the windings then the way you say that you have connected it should work. If there is internal bridgeing then when you connected A1 to Z2 and A2 to Z1 there will be a dead short across the mains.


geoff12/09/2012 16:59:13
29 forum posts

hi all

regarding motor and control gear wiring i think there should be a separate forum on here specifically for motors and control gear ie direct on line starters and invertors after all it is vital that they are wired up correctly

the invertor manuals are far too complex in their content for what is required by the model engineer for his workshop equipment be it a milling machine lathe etc

regards geoff

KWIL12/09/2012 19:10:50
3554 forum posts
70 photos

Geoff, If you find the Inverter Manuals too complex, surely this indicates that you should not be dealing with this equipment and should buy a complete setup from one of the established suppliers?

Wokauk12/09/2012 23:36:32
17 forum posts
3 photos


The motor did have the terminals bridged, removed them and then hey presto - it works.

Now to turn something, actually I need to bolt the lathe to the bench now and check that it is level........



Robin teslar03/11/2012 17:03:34
127 forum posts
8 photos

Ive got one of these motors for my ML7 and I wanted to ft a reversing switch. I found it useful but as you say, beware of the chuck unscrewing. Im going to fit a locking screw to be safe,

I often used reverse to cut thread away from the chuck. I didnt trust the feed screw knock out travelling towards the chuck, its not very accurate. Cutting away you can go much faster with confidence, and of course the form tool must be upside down.

I did this on a production job making 1000 special 1/2 unf bolts, worked a treat and finished in half the time to the amazment of my forman who had never seen such a trick, but then I was a cheeky apprenticecheeky

I will follow your guidelines but must order a Dewhurst (looks like /Chinese copy) on ebay 30 quid ouch


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