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myford motor

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Garry Martin 125/05/2017 15:06:06
13 forum posts

hi all I have been given a myford super 7 lathe it has a Crompton Parkinson motor and a Dewhurst rotary switch my problem is I cannot get it to go in reverse switch is wired up right and have power to both windings goes forward but not reverse tried every thing pulling hair out now grrrr any ideas why it wont go into reverse ?

John Haine25/05/2017 15:15:16
3422 forum posts
184 photos

Hi Garry, how frustrating!

If the switch is wired up correctly and the motor starts, that indicates that the capacitor is OK - but does the motor have its full power when running forward? But if the wiring is correct and the motor is OK, then only the capacitor can be the problem.

But in all the time I've had my Myford S7 the only reason that I've ever run the motor in reverse is when I want to brush swarf out of the nose threads.

Harry Wilkes25/05/2017 15:28:13
1003 forum posts
63 photos

Hope this helps link


Alan Wilkinson 125/05/2017 16:36:35
42 forum posts

Hi I ahve a Myford super 7 and like you I need to run reverse when cutting metric threads I had the same switch said reverse but went only forward, Ask lots of people who said it couldnt be done then asked a computer man and he said I can not see why so he came and had a look went away built a little box with a switch on wired this in now I just throw this swith turn on with normal switch and reverse it goes Just leave switch off for normal direction, If you aRE STILL STRUGLING i WILL GET HIM TO CONTACT YOU. just PM me He just charged me a pint

Georgineer25/05/2017 16:55:51
409 forum posts
20 photos

I presume you are allowing the motor to stop before switching it into reverse. If it is still running, it carries on in the same direction. I'll leave it to others to explain why...


NJH25/05/2017 17:06:32
2314 forum posts
139 photos

Hi Garry

Have a look here :-

motor plate.jpgmotor conns.jpgreversing switch001.jpg

Edited By NJH on 25/05/2017 17:08:34

Robbo25/05/2017 19:43:05
1504 forum posts
142 photos

As Georgineer says, the important point to note is that the motor must come to a complete stop before you change direction. If you do this and it still won't reverse then there is a wiring problem to investigate.

The Dewhurst switch changes the polarity of the windings- if it is still rotating it takes no notice and just keeps going.

Hopper26/05/2017 11:04:17
4868 forum posts
105 photos

Check its not something simple like a burnt out contact on the Dewhurst switch. This can happen if the Dewhurst is used for regular stop start duty instead of the dedicated pushbutton switch.

Howard Lewis30/05/2017 21:00:19
3755 forum posts
3 photos

According to the info that I have, and assuming that you have a Single Phase motor, the connections are: based on an intermediate Terminal Block between the Dewhurst Switch and the Motor, and the wire colours quoted).

1 - BROWN to 4 on terminal Block. SINGLE PHASE MAINS SUPPLY

2 RED to 6 on Terminal Block, then RED to Z1 on Motor

3 BLUE to 3 on Terminal Block. SINGLE PHASE MAINS SUPPLY


5 BLACK to 5 on Terminal Block, then BLACK to A1 on Motor

6 RED to 8 on Terminal Block, then RED to Z2 on Motor

7 BLACK to 7 on Terminal Block, then BLACK to A2 on Motor


If you have a 3 Phase motor, send me a PM. But be warned that I may not visit the Forum for a couple of weeks.


Howard Lewis06/06/2017 15:45:49
3755 forum posts
3 photos

Come on Garry,

Put all of us out of our misery!

Have you got it working; or was there a problem other than the wiring?


Garry Martin 108/06/2017 10:17:24
13 forum posts

Still cant get it to go in reverse brother is a top sparky at this type of thing and he is scratching his head

time to take motor apart I think

joey08/06/2017 16:51:13
31 forum posts

With most of the single phase AC motors one has to change the polarity on any one of either the running winding or the starting winding. This is done by means of either a reversing switch or 2 contactors with an interlock. Make sure the centrifugal operated starting switch is operating correctly.

Edited By joey on 08/06/2017 16:56:04

Garry Martin 128/11/2017 18:39:23
13 forum posts

yahoo sorted someones been in the back of motor and wired the terminals up wrong it should be AZ-A Z-T mine is AZ-T and A-Z so as soon as I realised that wired up accordingly bingo now got reverse happy days

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