Grangle inders.....what's going on?

Post by **Mick_Anik** » Wed Nov 04, 2009 8:58 pm

I'm in the process of repairing my Bosch angle grinder, and I'd like to ask a question about something which has puzzled me for years.

Inside, there is always a generous blob of grease around (ie nearby) the drive gear on the commutator and the driven gear which holds the disc.

The thing is, the teeth on the gears are always bone dry, probably due to centrifugal force throwing the grease away from them.

So why bother putting the grease in?

And how do the gears last for eons when they have no lubrication and run dry?

Post by **taupe** » Wed Nov 04, 2009 9:03 pm

Hi

Ive noticed the same thing.

I reckon that when it gets really hot it melts some of the grease and self lubricates!!

Post by **Mick_Anik** » Wed Nov 04, 2009 9:17 pm

Hello, taupe!

But the communtator has a fan on it......so just how hot does it get?

By the way, remember not to cover the vent holes in the body as you merrily grind away. This is easy to do when you are wearing thick leather gloves (which you should be wearing....steel toe-capped boots as well!)

Post by **alanworland** » Wed Nov 04, 2009 10:54 pm

Same with electric drills, you can push the grease back into the right places, then 10 seconds of running - and it's all gone again!

Post by **Mick_Anik** » Wed Nov 04, 2009 11:02 pm

Maybe there's a degree of vapourisation of the grease, which allows the gears to spin in a light mist of lubrication.

But the fan would blow this away!

Still confused, I'm afraid.

Post by **moggydriver62** » Thu Nov 05, 2009 4:23 am

Put constant velosity grease in there.
It sticks to gears.

Post by **les** » Thu Nov 05, 2009 7:49 pm

---and I thought I was a worrier, Mick.

Post by **rayofleamington** » Sat Nov 07, 2009 1:24 pm

And how do the gears last for eons when they have no lubrication and run dry?

The cheap ones don't have grease (cost saving) - as they pack up before the gears are worn.
In the good ones the grease will collect any metal chips that come off the gears - thus making the gears last longer. The gearbox itself should be properly sealed away from the armature / fan etc.. otherwise you'll be getting grinding debris into the gearbox.

As for how long the gears last - my Stayer angle grinder gears finally died after 18 years with fairly regular use. None of the cheap ones since have lasted 2 years, with the record fastest fail being less than 2 months (1 project).
I've gone back to a brand well known for robust products! 3 times the price of a cheap grinder but probably 10 times the lifespan.