Its nearly there !

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 25/03/2019 09:44:30:

 

Can anyone more knowledgeable comment?

.

I fail to qualify, Dave … But I am interested

This 'Instructable' includes some useful photos of the Dewhurst switch: **LINK**

https://www.instructables.com/id/Wiring-up-a-Brooke-Crompton-single-phase-lathe-mot/

MichaelG.

.

https://misterlinnsworkshop.wordpress.com/2014/03/08/dewhursts-big-switch/… and this post has a decent photo of contact pitting:

 

Edited By Michael Gilligan on 25/03/2019 18:37:01

[JonParticipant @jon]

Replaced and had to refigure Dewhurst twice within 8 years to 2000. Used to use a 1hp Brook Compton motor from the 1/3 HP as standard in original fashion where 240v feeds through Dewhurst then to motor. Could go through on/off as many as 50 times a night dont worry about it.

The contacts do get mucky but easily cleaned off but never bothered.

[SillyOldDufferModerator @sillyoldduffer]

Thanks Michael. In the pictures the switch appears to be well made, but the internet provides several clues:

• Bolt and locknut holding the drum segments together can slacken putting the individual switches out of alignment with each other and causing burn-outs due to poor contact.
• Suggestion rollers are made of steel, not ideal in a switch.
• Care required to ensure the metal case is earthed. (Modern requirement to connect metal covers with a separate earth wire is not met.)
• Contact opening and closing is slow, not speeded by spring loading, and making the Dewhurst unsuitable for switching under power.
• The circuit and switch type are mismatched by today's standards. It should be interlocked so the switch cannot be operated under power. A fast acting reversing switch could be substituted but isn't ideal because the motor should be stopped before reversing.
• Suggestion switch requires regular maintenance to check contacts are in good condition, lubricated and mechanically tight.
• Switch can be mis-assembled if taken apart for repair.
• Contact arms are prone to wear and bending.
• If arcing occurs, the insulation is prone to heat damage.

Many reports that Dewhurst drum switches fail after arcing, sparking or a burning smell is noticed. The list explains the why that's likely for a number of reasons – the design, materials, wear, and likely pattern of misuse all make the switch vulnerable.

I don't think any of this adds up to a need to rush out and change a serviceable Dewhurst! Despite the case for the prosecution, many Dewhursts have been trouble free for decades. But I do suggest failed switches should be replaced with something better, not with some antique off ebay!

Dave

[Dave SpringateParticipant @davespringate]

There is nothing g wrong with the Dewhurest drum ,I have I've stripped and cleaned it, repainted it and intend to make a new pointer / handle for it. I will not be fitting it though I will be keeping it with the lathe incase I want to use it in the future.

[Dave SpringateParticipant @davespringate]

There is nothing g wrong with the Dewhurest drum that I have. I've stripped and cleaned it, repainted it and intend to make a new pointer / handle for it. I will not be fitting it, though I will be keeping it with the lathe incase I want to use it in the future.

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