On Fri, 1 Oct 2010 17:59:15 -0700, "Michael Koblic"
wrote:

I also have a set of these boring bars:

http://www.busybeetools.com/products...47%7D2IN..html

which I have been using in my mini-mill. To use them on a lathe boring holes
in steel would you:

The textbooks say to place the tool slightly above center. The reason
being that the tool will not tend to dig in when it flexes downwards
due to cutting forces.

I am, however, not able to see how this is supposed to work. I see it
this way: The boring bar has equal stiffness in all directions. When
moving the tool higher, you are also changing direction of the cutting
force, and therefore also the direction in which the tool will flex.
What you achieve by setting the tool high, is to induce a slight
negative rake. This negative rake will, of course, create a force that
will try to push the tool away from the work, thus reducing the
tendency to dig in. In effect, setting the boring tool high with zero
rake is exactly the same as setting it dead center with a little
negative rake. The difference is that when the tool is set high, the
rake angle changes as the diameter of the cut changes, which is a bad
thing.

My personal recommendation: Set the tool dead center, and start with a
slight negative rake. Depending on the material you are cutting and
the stiffness of the boring bar, you may have to play with different
rakes to get a good cut. Remember that when you have changed the rake,
the tool height needs to be reset.
--
RoRo