"Bill Noble" wrote in
:

agree - wood dust from your lathe and sanding - you could try
compressed air to blow the dust out first, that might work - if it
doesn't, take it apart and burnish the contacts with 600 paper and
reassemble. Also make sure the centrifugal mechanism that actuates it
moves freely.

If it happens again, spin grinder fast by hand and turn on, it will
probably then just spin up to speed.

It's been so long I can't remember where it was, but someplace I
frequented (friends shop?) had a grinder like this. You got used to
giving the wheel a flick before hitting the switch, and off it went.
Fixing it properly had been on his "to do" list for years, but the time
it took to flick it into motion seemed so trivial compared to the time to
tear it down & fix it that the owner never bothered. It's probably still
like that if he's still around.

Doug White