Sick radial arm saw

[wristpin]

I have a US made Shopmate radial arm wood working saw made by McGraw Edison who are no longer in existence. I've had it for about 45 years from new and its been a useful tool but now has a problem. Originally the issue was that it occasionally tripped the RCD to the workshop when operated but now it's intermittently tripping it while just plugged in. I presume it to be an internal insulation issue of some description . Would welcome suggestions as I presume that normal motor rewind companies etc would not be interested but I don't want to rush to write it off.
230volt, single phase.

 

[Pete.]

I had a wolf bench grinder that did this and it was a capacitor in the base behind the switch.

 

[rtbcomp]

Is there a suppressor fitted? These sometimes have a capacitor from live to earth, if this leaks it could trip the RCD as Pete says.

You could disconnect it as a test.

 

[wristpin]

I had a wolf bench grinder that did this and it was a capacitor in the base behind the switch.

Thanks, but unfortunately no capacitor!

 

[daleyd]

If you haven't already it'd be worth replacing all external cables as a first step, as it's easy to do and cheap.

Motor rewind company might be worth a go, can't see why they wouldn't do it for the right price? You can always ask, you may be surprised.

 

[colnerov]

If it's tripping it whilst not switched on, I wouldn't have thought it was the motor. I would have said the problem was between the RCD and the switch.

 

[Wendelspanswick]

I had the same on my ancient Dewalt RAS and it turned out to be the flex running from the switch in the arm to the motor body, it might be worth running a flex direct to the motor to test it.
Is yours like this:

 

[AndyStobbs]

You say it trips when its plugged in, is there not a switch on the device? That is to say, the motor is wired directly to the plug?

 

[slim_boy_fat]

Does it have one of those moulded on plugs? Try cutting it off and fitting a 'normal' (rubber) one. After 45 years use it might just be a connection in the plug......

P.S. If that doesn't fix it, I'll give you 9p for it.

 

[brightspark]

u need an isulation tester to check it realy otherwise your just guessing if -theres earth leakage

 

[AndyStobbs]

See if you can strike the HF from TIG between earth and live terminals haha

No I'm not serious, but it would act like a Megger.

 

[wristpin]

Thanks for the suggestions. No moulded plug but it does have a trigger switch in the handle and yes it does have a coiled cable that is stretched as the body of the saw is pulled along the arm so I will investigate that next.

 

[brightspark]

take the leads of the motor and make a lead up with a 13 amp plug on and connect direct. if it trips its the motor if it doesn't -the faults in the lead or switch

 

[AndyStobbs]

Well if it trips before you've pressed the trigger, then it isn't the motor or inter connecting wire.

 

[wristpin]

take the leads of the motor and make a lead up with a 13 amp plug on and connect direct. if it trips its the motor if it doesn't -the faults in the lead or switch

Thanks to all who replied. Success with a direct connection with a fly lead so have taken a chance that it's not the switch and ordered a new curly lead .

 

[evobilly666]

Well if it trips before you've pressed the trigger, then it isn't the motor or inter connecting wire.

Would a neutral earth fault not still trip it assuming a single pole switch?

 

[KemppiFrog]

I also have a Shopmate 10" radial arm saw. Model 520013. Probably as old as yours. Bit noisy, due to it's geared drive, but that gives it a good depth of cut. I was given it several years ago as non-functional. Turned out the clutch in the drive was slipping, an easy adjustment. There is a guy in the States that has some parts for them, but not the 230volt armature, which looks a bit worn on it's gear end. It still works, but suffered when I lent it to the Ukranian workers on a project I designed. Ripping down big bits of timber was not what it was built for. Still useful though.

 

[AndyStobbs]

Would a neutral earth fault not still trip it assuming a single pole switch?

Fair point, well made. Think I would've done a little more testing before the spending though.

 

[evobilly666]

Fair point, well made. Think I would've done a little more testing before the spending though.

Agreed

 

[OldSteve]

Hi there
You didn't say if the flylead replacement worked?
I had the same problem with my Shopmate. Replacing the brushes solved my problem. They wear down past the carbon to a brass
pin at the end and I think that wears the commutator so that it can cause the RCD trip.
They were easy to change on mine - no disassembly required. Tilt the motor housing and there are some plastic screws that hold the brushes (one on each side).
I had an original spare pair of brushes from when I bought the machine but I see that someome sells a replacement.
https://www.solenttools.co.uk/parts-by-brand/shopmate/radial-arm-saw.html
If you still have the machine and the problem, check the brushes on your mcachine before you buy, you may have a different problem.