Is it an electric or air-operated angle grinder ?

You might take a look at the kickback brake on a chain saw for some ideas. The one I have on a Husqvarna chain saw is a band type brake that stops all movement almost instantly and it's simple.

If you're meaning to stop it rather than allowing to spin down. Pushing a wooden block against the edge of the cut-off wheel is a safe bet. The cut-off wheel should contact the wooden block as if it were to cut it.

Assuming it is electric (110 or 220VAC), then install a relay to short the phase and neutral to the motor together AFTER the mains has been removed. I can supply a small schematic if needed, just ask.

This will stop the motor in about 0.5 seconds. In fact good machines of this type usually have this already built in!!!

If its not electric, I give up!!!

This may discontinue power to the motor but not effect continued cut-off wheel rotation due inertia.

Thank you all so far. Re: slowing or stopping cutting wheel recently posted. Oops! There was a misunderstanding...I meant hindering or destroying the cutting action in a break-in/burglary situation with no-one but the "operator" present. Sorry to have misled you. Rod

I still don't understand it fully.......

The only way we stop the cutting wheel in Germany is to make a building of tubes, with greased free rotating shafts in every tube. They rotate with the cutter and therefore are cut immensely slowly only....but you cannot use it for a complete building!!!!

How about putting 10,000 volts on the outside when you are sleeping!!!!

I sell a burglar alarm here that detects any window being open or closed in any large 3 storey house up to 1000 square meters.....it works on pressure changes and the basic frequency of the house.....it does not need to be installed, just switched on.....

Contact me via email if you want more details, here is not the place to advertise.....

I may not understand what you getting at...

Some materials carry a "free Machining" designation while others are not easily cut:

Iron-Nickel-Chromium alloys; Stainless Steels; Copper-Nickel alloys; Nickel-Chromium etc. Cross hatch weld beads of Nickel Chromium onto the plate

Thin sheets encasing a material (Sodium etc.) which when heated may cause unpredictable injury, burns etc..

Produce EMF to an extent which would preclude the use of unauthorized electronic/electrical equipment

There are "seismic" type security sensors which are designed to detect drilling, CUTTING, burning, and other attack methods on safes, vaults, and ATM's. Can you use an alarm system to deter this activity? It should be cheaper and easier to implement than exotic mechanical countermeasures.

Bright lights and cameras even deter celebrities

"standard cut-off wheel on an angle grinder"

Does not square with, "

twist memory steel

as the cutter creates heat the steel

unwinds and binds the blade"

Jam the tire rubber into the wheel. Or, up......................

Pipes full of water under pressure. Include a permanent dye.

When the grinder cuts through, water spurts everywhere. Unlikely to short out his grinder, (although he will probably think so), but he will be marked and much easier for the cops to pick up.

Just getting sprayed with dyed water is likely to discourage him.

Unfortunately, you wind up with an almighty mess to clean up later.

My own solution is 2 dogs. The small one is the alarm and the large one the enforcer.

Have had at least 2 would-be thieves leave a lot faster than they came in.

As the large dog sleeps in front of the door, we don't bother to lock that door.

An interesting side effect is that since he has had the services of the small dog, the large one rarely barks, but leaves it to the small one. He simply sits there and looks on. "Why keep a dog and bark yourself?" seems to be his motto.

Hi Guest,

If you want to stay with the grinder you have there is two choices. One keep a suitable piece of wood handy and jam that in to stop/slow the blade.

Or, you can get a potentiometer to alter the speed from this sight, which BTW also does small grinders with speed controls already fitted.

http://www.nextag.com/variable-speed-grinder/products-html

I hope you find this useful. I think the other suggestion on a 'chain saw brake' or similar may also work? Sorry I cannot recall who suggested it.

Take care.

Please type slower, I am not able to understand your request.

If I understand, you are concerned about some thief using a small portable cutoff saw to remove something. If I am correct consider some inexpensive plastic. Either as a sheet covering the steel plate, or as a round bar in the middle of a pipe. What I have experienced when cutting HDPE, Nylon and PVC, is that as I try to cut it it will melt and coat the cutoff wheel and just bog the air grinder down. The only cure for this was to just stop, let it cool again and restart. Cutting plastic is always better I find with a toothed saw blade, rather than a cutoff wheel. The plastic may not stop the thief, but it should slow him down a bit.

If I did not understand what you were asking, again it is your fault for typing too fast. Good luck.