dewhurst lathe switch- electrical issues!

[nodeward]

so my smart and brown lathe has a dewhurst reversing switch like a myford. whilst using the lathe the other day there was a pop from the switch and some smoke and the rcd tripped. took the cover off to find this one of the copper fingers has srched arcross the insulating disk and burned a chunk off. it looks like the finger has moved from central and i can only assume this caused the problem.

so my question is this, does anyone have any experience of these and is this salvageable? there seem to be a few on ebay but as they are common to myfords they go for a decent price. i havent taken it to bits yet but i was considering making a new 'insulating disk' out of nylon or acetal or something but i am a bit worried as to why it arched across.

 

[500e]

The whole switch looks suspect the arcing, burning across the Bakelite could be due to 1/dirt 2/ weak springs 3/old age + either of first 2
Acetal has good insulating properties use natural color less likely to have no or low carbon content or there is Tufnol 6L\45
Remember Nylon has a habit of absorbing water I think 2% is a figure in my mind

 

[Agroshield]

Looks very repairable. Give everything a polish with Scotchbrite before reassembly.

Are you aware that these should not be used to switch power under load? Doing this is the single biggest thing that reduces their life. They should only be used to change the route of the current. They also lack a no-volt-release capacity. If you have a NVR switch in the circuit, this is what should be used to operate the motor. If not, then consider fitting one (Auto Memota is a good one and of the same period and style as the Dewhurst).

 

[armalites]

Are you aware that these should not be used to switch power under load? Doing this is the single biggest thing that reduces their life. They should only be used to change the route of the current. They also lack a no-volt-release capacity. If you have a NVR switch in the circuit, this is what should be used to operate the motor. If not, then consider fitting one (Auto Memota is a good one and of the same period and style as the Dewhurst).

I guess like many users I did not know that and I have always used it to operate my ML7. I will look to remedy that

 

[brightspark]

its a reversing drum and an on and off switch just don't reverse it while the motor is still running

 

[nodeward]

Cheers guys. Yeah it was pretty dirty, I think I will try and take it to bits at the weekend, we probably have some acetal kicking around at work I can use to make up some new disks.