There are actually three kinds of diamond drills available. Plated,
sintered and brazed.
The first one, plated, I'm sure most are familiar with this one. The
diamond is a mono layer that has been applied to the steel substrate
by an electronic bath process. This process is the most common type
but has the shortest life and is not very consistent. It tends to
over heat and peal the nickel adhesive coating. Very inexpensive too.
The second one, sintered, is a multilayer and has no steel substrate
except for the butt end of the drill bit which is chucked into the
drill. The diamond is throughout the thickness of the core or as in
a hollow, or core drill, the wall thickness. These last quite a long
time but will loose the actual diameter due to the wearing of the
metal that is mixed with the diamond while drilling. These also tend
to clog more and loose their cutting ability over a short period of
time. Sintered can be re dressed with a silicon carbide dressing
stick when it becomes clogged but once again you will loose the
actual diameter of the drill. Sintered drills can become very thin an
can fly apart at some time. Be very careful. Sintered drills are
The third kind, brazed, is a mono layer of diamond that has been
welded with flux and extreme heat to the steel substrate. because of
the application with extreme heat the diamond has no chance of
pealing as the bit gets hot from use. Unless, of course you are
getting the thing red hot then you have bigger problems. If any thing
the diamond itself is friable and will crumble under undue heat and
pressure or just round off due to use in the same direction of
rotation. Because of the diamond application process, these tools are
more consistent across the board. And because of the mono layer and
no metal holding the diamond in place the tools has more air space
around each diamond giving each diamond more ability to cut without
clogging as fast; making it a more aggressive drill. The price of
brazed tools falls somewhere in-between the plated and the sintered.
The quality of the drills depends a lot on what drills you are
using. If made in China, the quality may vary widely...especiall
if they are the plated variety. You might want to try
'triple-ripple' drills. They are moderately priced but cut
effeiently and the quality seems to be standard.
As far as I know "Triple Ripple" drills are the only drills on the
market that are brazed. Not only are they brazed but they are also
fluted to allow for more efficient swarf removal. Crystalite Corp.
manufactures them. They do come in a 2.1mm size. I have no monetary
interest in them.
I agree with all of the other suggestions with regards to speed and
backing (wood works too) but I will add that a 5% solution of ethyl
glycol be used with water. Drill fully submerged. Use a light hand
and let the diamond do its business. Also release the pressure and
lift the drill out of the hole, while running, to help flush it and
the swarf on the bit regularly. Slow down and very light pressure at
the end will lessen the blow out. I recommend to make a dimple with a
diamond ball burr approx. the same size as your bit to start just
like making a center punch on metal.
Also a note about why the lasting qualities of drills with different
stones. Different stones have different abrasive qualities on the
metals that are holding the diamonds in place. So some stones will
wear away the metal thus releasing the diamond before its time.
Talk about boring.... yet informative. Got to go... the lightning
and thunder is here! OOOOh Weee first of the year! Happy cutting!
Elayne K. Luer, GJG