For Dapping holes in a very hard wood knot.
Depending on the size depressions you want to make. For small domes
you could get router bits called a “Core Box Bits” which are meant
to cut a groove with semicircular cross section, These grooves are
used for packing and shipping geologic core samples collected in the
field back to labs for testing. I have seen them in several sizes,
but not in a great variety of sizes. that is, I doubt you’ll find a
set of them going from 1/4" to 1 1/2" in 1/16" increments - but you
should be able to find a few sizes.
You will need a router (ideally) but I think for this purpose you
could get away with using the bit in a drill press.
If using a router, Instead of running the router along the wood to
make a groove, you would just lower the bit straight down into the
surface while keeping the router stationary thus producing a
If using a drill press, set it to run at the highest sped possible
(which will still be slower than the bit is designed for), fix the
wood firmly to the drill press table and gently drive the bit
straight down to make the depression you want.
I don’t think you’d have much success using any kind of hand-held
drill or flex-shaft.
Much cheaper than router bits - but more work for you – you could
get a set of cheap wood boring “paddle bits” (also known as “spade
bits”) which are easily available in a wide range of sizes. They
typically have a 1/4" diameter shaft with flat paddle-like bit at
the business end. Grind off the centre point which protrudes at the
business end of the bit and regrind the profile of the paddle so the
profile of the bit end is a semi-circle of the same diameter as the
bit’s diameter. Then grind and hone the edge of that semicircle with
a rake angle similar to the rake you can see on the edges of the
paddle. It will probably work in a drill press, especially if you
shorten the bit’s shaft to reduce vibration or bending which might
set up a chattering when trying to cut. Pay attention to the bit’s
direction of rotation when you set out to grind the rake angle so
the cutting edges on either side of the bit’s centre will both be
facing forward, so to speak, when the bit is turning. Again, fasten
to workpiece to the drill press bed, set speed high, cut slowly with
light pressure. Should work.
These are probably not the ONLY ways to do this, but they’ll do.
Marty in Victoria