Geeze, Ed ! Thanx for the information; esp. the research timeline. My curiosity re. lard oil comes
from reading old books and articles. Its use was apparently de rigueur in the old days. I have not
found any modern definitions of the term, except for yours. Personally, it is more of a historical
curiosity with me. I generally use Tap Matic for turning and the Black Sufphurized mess for
threading.
Bob Swinney

They're not direct replacements, Bob. What is it that you want to know about
lard oil? It's been around for a century or two. It's just lard that's been
chilled until the stearin crystallizes, which allows the oil to be pressed
out of the goop and drawn off.

The lubricating properties of lard oil and unmodified mineral oil can be
similar, but the additives and some of the synthesized components used in
mineral-based lubricating oils give lubricating oil and cutting oil
radically different properties. Oil made for lubricating has properties that
are not good in a cutting oil. Motor oil is lousy cutting oil. It's made to
*prevent* local contact under high pressure, although its ability to do so
is limited at cutting-tool pressures.

Heavy thread-cutting oils have good cutting-oil properties except that they
don't get into the cut in a machine tool, so they don't do anything in a
deep cut. You want something that gets in there. Plain lard oil and the
non-lubricating mineral oils, formulated for cutting, will do that to some
degree. However, research (done mostly at Carnegie-Mellon Univ. in the
1950s) shows that they don't get into the cut as much as some people have
claimed over the years.

Basically, you want a cutting oil not to squeeze out under pressure, but you
want the film to puncture easily upon point contact. These are somewhat
contradictory properties but there are some additives that will help do it,
including white lead and sulfur. There are modern replacements for these.

Beyond that, there are chemical additives that actually get into the crystal
structure of the workpiece and help separate the grains when they're cleaved
with a cutting tool. Chlorine compounds will do this on some work materials.
So will carbon tetrachloride. Chlorine has been taken out of most cutting
oils because it forms carcinogenic compounds at the tool/work interface,
where the temperatures are locally very high. Carbon tet was never used in
commercial cutting fluids. But it was tested extensively at Carnegie-Mellon,
and the way it works is amazing. Unfortunately, it tends to kill machine
operators. d8-) I've used it. Some gage makers used it on hardened steel, a
century ago. They're all dead now for various reasons. I'm on borrowed time
myself. g

Modern high-performance water-miscible cutting oils ("soluble" oils) contain
chemical additives that are safer and that have some of the properties of
chlorine in a cut. Blasocut and other fancy-schmancy oils rely heavily on
the properties of these additives, I've been told by their vendors. I'm not
much interested in them for hobby work so I'm not up to date on these
fluids.

Plain lard oil, like Buttercut and some others that are still on the market,
are fine for the hobby shop. So are the simple mineral-oil cutting oils that
DoAll and such have sold for decades. I think that cooking up your own, or
using slop like used motor oil, is false economy and may be dangerous.

--
Ed Huntress


** Posted from http://www.teranews.com **