Breaking Bits

Quoted text begins.I broke three bits in very short order. The last one inch
or so would just twist off, right about at the blow holes.
Is that where yours broke?
End of quote.

Just so, Bill. The supplier was very unco-operative and insisted
that the drills were not meant for drilling granite, only 'soft'
materials like
concrete. Fair dinkum! So why are they called a 'rock drill' ?

I must say I persisted with the Atlas Copco drill bits longer than I
should have. Apparently there is not a genuine AC drill bit, they just
get them
from whoever has them in stock at the time, be they German, Asian,
American manufacturers. We were using about 6 bits for each class,
and cost was ridiculous. The last straw was when I broke a new bit after 2
holes, and the supplier denied that the bits were faulty.

You're right about the touch. Unexperienced operators either push too
hard and make a curved drill hole, getting the drill stuck, or they
don't push hard enough. 'Blank firing' (operating the air drill
without load) wears the nose components of the drill really quickly.

The solid drill bits have a double helical auger to lift the dust out
of the hole. Makes them less dusty to use when the dust is not
being blown out of the hole.
I don't use a blower, just a brush at the stone surface.
The K-taper acts as a safety clutch so the tip doesn't get
torqued off. The steel in these bits is definitely less brittle
than the AC hollow bits. We didn't break a single one in the last class.
One got a little bit bent, but it's still OK for drilling around corners.

Simon