3 pole or 4 pole for a reversing switch?

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3 pole or 4 pole for a reversing switch?

This topic has 11 replies, 8 voices, and was last updated 8 September 2016 at 13:52 by not done it yet.

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7 September 2016 at 22:20 #254667
mrbuilder
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@mrbuilder
I’m wanting to purchase a new drum switch for my ML7 (single phase). I’d prefer a new switch as opposed to a classic Dewhurst unless I stumble upon one in great condition.

Anyway, my question – is the any advantage to 3 or 4 pole drum switch configurations? Any reason you’d choose one over the other?
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7 September 2016 at 22:20 #31852
mrbuilder
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@mrbuilder
7 September 2016 at 22:28 #254668
NJH
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@njh
Just enter "reversing switch" into your browser and there will appear a lot of options!

The question I have though is why do you want a reversing switch.? I've not found a need to run my lathe in reverse and, with screw on chucks, it's not a very good idea!

Norman
7 September 2016 at 22:36 #254669
Les Jones 1
Participant
@lesjones1
With a 4 pole switch you can isolate the motor totally from the supply when in the off position. With a 3 pole switch one side of one of the windings (Normally the run winding.) would still be connected to one leg of the supply (Normally the neutral.) when the switch was in the off position. This would mean that if you only relied on the reversing switch to switch the motor off AND live and neutral had been swapped over the you would be electrocuted if you touched either terminal on the run winding of the motor.

Les.
7 September 2016 at 22:51 #254671
Harry Wilkes
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@harrywilkes58467
I use one of these http://www.ebay.co.uk/itm/QS-30-Drum-Switch-Forward-Off-Reverse-Motor-Control-Water-Resistant-30-Amp-UR-/371706951395?hash=item568b75f6e3:g:iCcAAOSw-itXqzEy

Ok it leaves one winding connected to the neutral but I dont see a problem (a) any 13amp unswitched socket will do the same (b) I use a starter (c) I alway switch off the power to the lathe when I have finished with it !

Also remember run in reverse can cause the chuck to screw off

H
7 September 2016 at 23:00 #254672
mrbuilder
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@mrbuilder
Posted by NJH on 07/09/2016 22:28:44:

Just enter "reversing switch" into your browser and there will appear a lot of options!

Yes thanks but I don’t need to know where to get one from, I have already searched for them and know where to purchase. I’m after the specific difference/advantages between 3 and 4 pole versions.
7 September 2016 at 23:00 #254673
mrbuilder
Participant
@mrbuilder
Posted by Les Jones 1 on 07/09/2016 22:36:29:

With a 4 pole switch you can isolate the motor totally from the supply when in the off position. With a 3 pole switch one side of one of the windings (Normally the run winding.) would still be connected to one leg of the supply (Normally the neutral.) when the switch was in the off position. This would mean that if you only relied on the reversing switch to switch the motor off AND live and neutral had been swapped over the you would be electrocuted if you touched either terminal on the run winding of the motor.

Les.

Thanks this was the information I am after – I’m likely to get a separate on/off switch fitted so a 3 pole might be sufficient.
7 September 2016 at 23:04 #254674
mrbuilder
Participant
@mrbuilder
Posted by Harry Wilkes on 07/09/2016 22:51:04:

I use one of these http://www.ebay.co.uk/itm/QS-30-Drum-Switch-Forward-Off-Reverse-Motor-Control-Water-Resistant-30-Amp-UR-/371706951395?hash=item568b75f6e3:g:iCcAAOSw-itXqzEy

Ok it leaves one winding connected to the neutral but I dont see a problem (a) any 13amp unswitched socket will do the same (b) I use a starter (c) I alway switch off the power to the lathe when I have finished with it !

Thanks, that's cheap I might give that version a go. I use the same "safety procedure" with my wood lathe.
8 September 2016 at 09:43 #254714
Bazyle
Participant
@bazyle
I received a motor recently wired to a reversing switch and used as the on/off. Haven't looked yet to see what damage the sparking has done to the contacts.

Queston : is it worth using a starter (ie an on off incorporating a thermal cut out) rather than just an NVR no-volt-release on a small domestic motor. I have one no my other Boxford but it came with it (probably 60 years ago so no telling what the setting is).
8 September 2016 at 12:03 #254738
peak4
Participant
@peak4
Posted by NJH on 07/09/2016 22:28:44:

The question I have though is why do you want a reversing switch.? I've not found a need to run my lathe in reverse and, with screw on chucks, it's not a very good idea!

Norman

In my case, when cutting metric threads on an imperial changewheel Myford Super 7.

One mustn't loose the leadscew engagement between passes, and the saddle thread indicator is only of use for imperial threads.
8 September 2016 at 12:23 #254742
KWIL
Participant
@kwil
peak4,

If you intend to do a lot of screwcutting as I do on a Super 7, there is a single dog clutch reverser (Graham Meek designs) which allows the motor to stay in normal. (I have one fitted).

I also have available (to my own design), a chuck locking device which will prevent the unscrewing if it became really necessary.

K
8 September 2016 at 13:52 #254757
not done it yet
Participant
@notdoneityet
Peak4,

Apart from thread cutting, there may be occasions when one might prefer to cut on the 'other' side. These lathes do have a morse taper in the spindle, so do not always require a screw-on chuck for operation?
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