autostop brushes in Hitachi Angle Grinder

[desbromilow]

Just letting everyone know in case you find this in the future...

my Hitachi angle grinder was working fine doing a cut, and when I picked it up to restart after adjusting the placement of the metal, it would not start. Acted as if the breaker had tripped.
Breaker was all good, checked everything and eventually found it was acting as if the brush to commutator connection was open.
I pulled the brush and found a small (~1.5mm (1/16") diameter nylon pin sticking out the face of the brush. This small pin was spring loaded and had lifted the brush off the commutator, effectively stopping the machine, and stopping the worn brush from arcing and burning the commutator.

It's a machine protection feature called "auto stop"... deviously clever and very effective.
Replacement brushes are on order, and the autostop version cost about $10 more than "normal" brushes.

How can you tell if you have them? In my case, the brush has 2 holes drilled in from the back, one hole has the brush lead captured in it, the other hole simply appears "filled" with a copper paint. - This second hole is the one containing the autostop mechanism.
I've used that grinder a LOT over the past 14 years, so it hasn't shortened brush life at all, but has protected a great machine and I'm hoping once the new brushes are fitted, I'll get another 14plus out of the machine.

SO... if you have a decent brand machine which "suddenly stops working", it might be worth checking the brushes in case you're facing a similar installation.

Des

[clavius]

Wow, that's a great idea and a good feature, really. I'd never heard of that it's good to know.

I recently burned up a favorite Milwaukee side grinder that I'd had for at 30 or so years when one of the brushes broke a corner off, jammed into the commutator and shorted it out. I should have been more attentive and yes, I should have replaced the brushes after 25 years, etc. I know. But I didn't. This would have protected me (or more correctly, my grinder) from myself.

That setup you describe is the definition of an "elegant solution"!