DIYbanter - Boring Hole Help

On 18 May 2005 07:23:19 -0700, "JEP"
wrote:
i need to bore a 2.5 inch hole in a piece of 3inch OD, 2 1/8ID pipe
5 inches deep, all i have is a vertical mill,
3inch quill travel, and 8inches of up/down table travel.
i do not have a lathe,
i was thinking of buying a 2inch boring bar head, from grizzly,
any help opinions apriciated,
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If this is a one-time job (and you you are not looking for a
reason to buy a boring head) you can use a lathe boring bar with
some modifications and a special grind on the tool.

IMPORTANT == Because the tool bit in the typical boring bar is
set above center you will need to either grind the tip of the
tool 1/2 off to get it to center or grind in considerable back
rake or hook to get the same effect.

Buy as large a boring bar as your milling machine can accept with
the right angle tool position. 5/8 and 3/4 shank diameter boring
bars generally use 1/4 square tool bits. Cost is c. 7.50$US w/o
tool bit. Given your bore size you may want to go for a larger
boring bar and if you have or can get access to a lathe turn the
end down to your largest mill collet size.

Modify the boring bar by drilling a hole about an inch above the
square hole for the tool bit parallel to the tool bit axis. A #5
drill [0.189 inch diameter] is about right for a #10 screw.

At right angles to the #5 hole drill and tap a 10X32 hole for a
set screw.

Take a two inch piece of 1/2 square keystock and drill and tap a
10X32 hole about 1/2 inch from from the end centered on the long
axas and perpendicular to the face of the key stock. Loctite (or
jamnut) a long 10X32 screw [I like an allen bolt because these
are hard] into the 10X32 hole in the keystock and cut the head
off. [you may want to mill the face of the keystock flat first.]

To use, you put the shank of the screw in the keystock into the
#5 hole in the boring bar with a feeler gage between the end of
the tool bit and the keystock. Clamp the 10X32 screw in the
keystock in the boring bar. Remove the feeler gage. Loosen the
tool bit clamp screws, gently push the tool bit up against the
key stock and reclamp the tool bit. Whle this requires 3 hands,
it allows you to bore to a thousandth [most feeler gage sets have
one blade with a nominal plus 1/2 thou. thickness].

You can use a boring bar with the bit at an angle [used for
boring flat bottomed holes] by using a longer piece of keystock
for the gage. This won't be as accurate because of the
additional flex. Be sure the gage is long enough because as the
hole gets bigger the further the bit will extend below the end of
the boring bar.

Lathe boring bar is still usable as lathe tool.

Let us know how you make out.

GmcD