Air micro die grinder review

Page 3

I broke off a quality 1/8" HSS thread tap in the flywheel of a model engine I'm building. 

The firmly lodged broken tap can be seen above.

It refused to come out using the usual methods, and as I didn't have a spark eroder, I thought why not try grinding it out with a round nosed carbide burr.

20 minutes later.

The tap is gone - pretty amazing.

I then redrilled the hole to a slightly larger size, and used a small friction disc to cut a rolled steel pin to length.

To finish the job off nicely below.

flame licker

So it saved the day, and the cam lobe is now held in position against the flywheeel by a rolled steel pin.  Considerable re-work saved, and the small design change made a neater job.

I also had to drill a hole in a 0.003" feeler gauge as a valve for the little motor.   Normally this would be extremely difficult with a twist drill as it will catch and tear the thin metal.

The micro grinder did it easily and perfectly using a pointed carbide burr - see below.

pointed burr

I simply centre punched the metal to give the burr a slight depression to get started, and then guided it through into a block of soft wood.

It's a great little tool, and very easy and accurate to hold and use.

Only light pressure is required - eg for all of the above.

There is no heat build up.  In fact, the faster it spins, the colder the body gets as you put more air through it.

Wear safety glasses to protect yourself from fine cuttings, and any potential disc failure.


Anything that fits a Dremel rotary tool will fit these micro grinders.

However, as these units can spin at such high speeds, you should be very careful not to overtax the capability of the attachment.

The instructions may even recommend against using certain attachments which the manufacturer considers potentially dangerous - eg, cutting discs.

The smaller (less than 30 mm) non-fibre reinforced discs most certainly should not be used at high revolutions, as they can easily disintegrate.  

The items below were in one of those multipurpose kits that are sold on Ebay.

Dremel rotary tool fittings

Tungsten carbide burrs are very handy and come in a variety of shapes and sizes.  The bigger the diameter of the cutting tip, the more expensive.

Straight 3 mm burrs are equally effective, and a lot cheaper.

It is recommended that for long burr life the speed should be kept down
when used with hard metals such as steel.

Same thing for abrasives.  The safe rotational speed of small diameter grind stones and cutting discs is almost certainly less than the maximum speed capability of the die grinder.

The fine wire shards from rotary brushes are particularly hazardous, and can easily fly off and cause injury.

So be very careful, and wear safety goggles at all times when using one of these units.

Tool post mount

It's easy to make up a simple mount which enables the air grinder to be used as a sort of (very) mini tool post grinder or mill head on your lathe.

The design below grips the die grinder at it's strongest point, quite safely.

mini tool post grinder

Can be used for indexing with the chuck and can do some surprising things.

Seen below where I use it to cut piston rings.

Open out a small hole in very hard metal,

and sharpen end mills.

You can see the results on the next page.

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South Australia