core drill bit

[John Twilley <jtwilley@zzzzzzzzzzz>]

Sounds like a couple of problems.  A drill that is 1.5" in diameter
with a flat end has a great tendency to walk across the surface unless
both the drill and the work are anchored.  You might consider starting
the hole with a cheap carbide hole saw of the type used for cutting
holes in countertops.  These come equipped with a centering spade
point drill that can be removed after the first few millimeters, once
the core drill has entered the work.  You could substitute the longer
diamond drill at this point.

Secondly, what is the diamond drill intended to cut?  A drill intended
for a soft stone like marble needs to have relatively coarse abrasive,
while one intended for granite or similar is often fine.  Using the
later on marble will typically cause the marble dust to become
impacted within the abrasive and slow or stop its progress.

You're using it dry but are you using an airstream in place of water
to eject the cutting dust and keep the tip cool?  Just because it is a
"dry" bit doesn't mean that you can use it without a means of cooling
or ejecting debris.  This will be a big factor in preventing the bit
 from becoming impacted as the hole gets deeper. If you don't provide
some cooling you're in danger of losing the the sintered diamond from
the tip.  But also beware of condensation from the compressed air line
if it lacks a drier.  Sometimes a few drops of water ejected into the
hole will provide just enough moisture to make the marble dust sieze
up on the drill.

Bottom line, if you don't need high tolerances (could an angle grinder
give you that?) You might be better off using a countertop hole saw
and adding extensions to its shaft, taking the core out in short
segments. I once did a dry hole 30" deep into a shale wall that way
that could not have been done with a diamond drill.

John Twilley

Zhivago97@------- wrote: