I need to make a drill extension guide to finish a project. I want to use a
..090 end mill to manually peck drill a hole in angled face deep in the
cavity of a mold. I can get a shot at it with a long bit. I was thinking I
would make an 1/8 bit holder extensions six inches long to do the job. That
would probably be adequate in itself for this job, but I was thinking I get
get within a few thousandths and reduce risk of spin damage by running the
"extension" through a guide with one end machined to wrap around the
protrusion where the face I want to drill is located.

The thing is I don't have a lot of room to work. About .185 clearance on
one side of the extension from center. I could turn a piece of stock down
to .36 just fine, but then I would be limited in the main diameter of the
extension to about .25 or less.

I need about 6-7 inches of reach. I have some aircraft drills in
appropriate sizes, but my experience is that they tend to flex and wander
after more than an inch or two.

You know, I think I am just going to make the extension for now and get the
job done, but how would you tackle it the other way I described. Remember
there isn't much point if it doesn't start out big enough so one end can be
machined to set in place...

Bob La Londe wrote:
I need to make a drill extension guide to finish a project. I want to use a
.090 end mill to manually peck drill a hole in angled face deep in the
cavity of a mold. I can get a shot at it with a long bit. I was thinking I
would make an 1/8 bit holder extensions six inches long to do the job. That
would probably be adequate in itself for this job, but I was thinking I get
get within a few thousandths and reduce risk of spin damage by running the
"extension" through a guide with one end machined to wrap around the
protrusion where the face I want to drill is located.

The thing is I don't have a lot of room to work. About .185 clearance on
one side of the extension from center. I could turn a piece of stock down
to .36 just fine, but then I would be limited in the main diameter of the
extension to about .25 or less.

I need about 6-7 inches of reach. I have some aircraft drills in
appropriate sizes, but my experience is that they tend to flex and wander
after more than an inch or two.

You know, I think I am just going to make the extension for now and get the
job done, but how would you tackle it the other way I described. Remember
there isn't much point if it doesn't start out big enough so one end can be
machined to set in place...




You said you have aircraft bits. How about making a few drill bushings
then tack them together to create a long bushing that you could then
feed the drill through. Sort of like a mortising attachment for wood?
The drill would run inside the guide and the flex and wander would be
contained.

--
Steve W.