electric motor

[Digit]

Are you absolutely certain that neither of the brushes were jammed? Modern electric motors are normally not bothered about getting wet, provided, as I pointed out earlier, they are allowed to dry out before use.
But carbon brushes will definitely soak up water, this can soften them and cause them to stick, this will cause heavy arcing and burning.
The brushes should be free to slide, any stickyness would be bad news.

Roy.

 

[jonny boy]

It's funny you should say this because it's been niggling at the back of my mind obout the brushes. The brush holders have been scorched by the exessive sparking and the brushes themselves are certainly softer than any i've seen before. I checked to see if they slid freely in their holders and while you could move them up and down, there was a little resistance but I don't know wether it was enough to cause them to stick.
Bob has kind offered to check the armature for me if I get it posted to him which i'm going to do tommorrow and i'm sure he'll let us know on here as soon as he's had time to test it.

jonathan.

 

[9fingers]

The brushes should be free to slide with less effort than the spring can exert.

If they stick at all then a touch with a fine file should free them.

If the brush boxes are discoloured by the heat, is there any hint of the plastic melting? This can be bad news.

Bob

 

[jonny boy]

The plastic boxes that hold the brushes aren't melted anywhere but on the yellow plastic of the motor casing near the brushes, there has been a sign of some melting and blackening. When I press the start trigger only for a couple of seconds, there is noticable heat build up in the brushes and around that area.

jon.

 

[Digit]

If the brushes have softened then what I have seen in the past is that a heavy coating of carbon dust builds up on the brush holders, with an increase in heat and arcing. What ever the outcome of the armature test a thorough clean up is on the cards.

Roy.

 

[jonny boy]

A heavy build up of carbon dust is certainly on the menu! It's caked in it around the problem area, well it was before I wiped most of it away.
At work, we have several Dewalt saws and one in particular is used about every 5 mins throughout the whole day and has been doing so now for the best part of 12 years and still on the same brushes from new. It baffles me why some tools can run forever totally unserviced and overused in some cases.

jon.

 

[Digit]

Softening of brushes causes them to wear rapidly, both from friction and arcing as well.

Roy

 

[jonny boy]

It seems I may have had a little luck for a change. I sent the armature off to Bob who kindly tested it for me and fingers crossed, he seems to think it's OK and a new set of brushes and armature bearing could be all it needs. Good to have helpful members involved in the forum.

jonathan.