"Karl Townsend" wrote in message
...
On Sun, 29 Sep 2013 17:51:11 -0700, "PrecisionmachinisT"
wrote:


"Karl Townsend" wrote in message
. ..
I'm trying to bore a 1" hole 12" to 14" long in a 1.75" square rod
PERFECTLY on center to my CHNC lathe...

Not an easy task. I wouldn't ask if it was easy. OK, a slight
misalignment at the center won't bother, so now I only need to bore
7".

My best idea to get it in perfect alignment is to mount an end mill
just under one inch in the spindle and bore with the square rod
mounted in position on the lathe. Then take the part out and bore to
correct diameter in the mill.

I just searched my stash, found a 5" long by 7/8" EM. I'd sure like
to find a longer one. Anybody have one? Quick search on fleabay, no
joy.

FWIW, I'm trying to gundrill 24" long in a lathe with 12" travel. The
drills mount in a one inch bore.


You just need a long holder; the endmill can be one of those cheapo 1/2in
shank jobbies like Enco sells for hand mills although I would probably
first
go through with a slightly undersized silver and deming, retracting fully
at
very frequent intervals.


Thanks for the idea. I didn't know they made 1/2 shank by 7/8
endmills. Just the ticket.

Yes, i didn't mention, I'll ruff drill it first. Just use the endmill
to true it up.


Alternate between a 7/8 in S&D drill and an endmill 1/16th or so smaller
than the finish hole that's been cicular ground and has about 1/2 degree of
backtaper , switching back to the drill after every inch or so in depth,
then finally, run your finish tool, removing .03 or so per side, preferably
in a single pass.