P,


You may want to check out "trepanning".
Trepanning is a machining method of producing larger diameter, deep
drilled holes which can be more cost effective than typical gundrilling
techniques.  It is best described as core drilling.  Unlike gundrilling,
Trepanning leaves a core from the center of the bar instead of turning it
all into chips.


One vendor, easily found with a Google search is:

Trepanning Specialties, Inc.
16201 Illinois Ave., Paramount, CA 90723
Voice (562) 633-8110 . FAX (562) 633-0141
More than likely... many others.

Jack Beale

According to Google this is a methods of drilling holes
in skulls.

Paul Lamar


True Paul,
But it it also cutting a slot at a diameter without a center. A hole saw is
multi-tooth trepanning.
Bill Jepson


I contact the company and to get a 4 inch core OD out of the center they
would have to start with 13 inch OD. Where are you going to find
13 inch OD ??? :)

and it would cost about $120 dollars.

Paul Lamar

Here's another stupid question from a guy who can count the number of
times I've used a milling-machine on my fingers ...

Can't you in effect do trepanning with a CNC mill?  Maybe you'd have to
flip the piece over and work from both ends, but you should be able to
mill out a circular slot (crude though it might be)??

R Berglund

Yes it can be done. It is called circular interpolation. To do 12 inches long means
you need a long cutter and long cutters bend. It  might work with a 3/4 inch
custom made long cutter. Ultra Tool company with a 7 inch reach the tool
cost $595 from Rutland tool and supply. A one inch diameter version is
$935.


Paul Lamar