On Jun 27, 3:45*pm, Joseph Gwinn wrote:
In article
,
*"Denis G." wrote:







On Jun 26, 3:14*pm, Joseph Gwinn wrote:
In article ,
*Bob Engelhardt wrote:

Joe's recent thread about his dribble cooling for his lathe reminds me
of questions that I have.

1. *What is the purpose of cooling? *Does the tool get so hot without it
that the edge is dulled? *I thought HSS & especially carbide could stand
the temperatures created by HSM work.

The first purpose of cooling is primarily to prevent welding of chips to
cutting tool, which causes effective dulling. *The second purpose is to
keep the tool itself cool, so the cutting edge won't become soft. *With
modern tool steels and carbides one can go far faster before this
happens, but cooling always allows one to go faster than dry.

2. *What is the purpose of cutting oil? *I remember reading that it
allowed chips to flow off the cutting edge more easily. *Is that it?

Reduces cutting force by lubricating the interface between tool bit and
workpiece. *This usually results in better surface finish, and may yield
better accuracy as well.

3. *Does choice of cooling or lube depend upon the tool (lathe, mill,
drill press, band saw), or material? *Or both? *

It mostly depends on the material being cut. *This is discussed at
length in Machinery Handbook.

Coolants have various combinations of cooling effect and lubrication
effect. *Plain water (used when machining some plastics) is a pure
coolant. *Wax is a pure lubricant. *Oil in flood is a lubricant with
significant cooling ability. *Oil emulsion in water does both. *And so
on. *One can make a career of this.

[snip]

There are tables in the Machinery Handbook.

If you really want to dive into the details, there is a book, a tome to
be precise. *There was a thread on this titled "Metal Cutting
Principles, the tome" posted on 14 April 2007. *

The book is "Metal Cutting Principles", 2nd edition, Milton C. Shaw,
Oxford University Press, 2005, 651 pages. *

I will say that parts of this book are very heavy going.

Joe Gwinn- Hide quoted text -

- Show quoted text -

Joe,

I noticed that Shaw has a doctorate in chemistry. *(http://tinyurl.com/l27kaq) *Does he use chemical explanations for the role of sulfur in helping

It's quite the tome. *Although it did scratch the itch, it was far more
than I wanted to know. *Glad I got it from the library.

Does he use chemical explanations for the role of sulfur in helping metal
cutting operations? *(sulfur cutting oils/high sulfur steels)
It seems unlikely that a chemical reaction would have time to
influence cutting, but who knows. *

This was a big question, for exactly that reason. *It turns out that the
effect *is* chemical. *The tests consisted of soaking a test piece in
carbon tetrachloride or whatever, and then machining the test piece
after waiting for various periods of time or heating the piece, et al.

The high temperature and/or severe mechanical shearing forces split the
molecules, releasing the sulfur or chlorine atoms which then combine
with the atomically clean just-created metal surfaces, preventing
welding back together.

How the molecules get to the point of use is still a bit of a mystery,
but otherwise it's well established that they do. *One theory is that
the mechanical strain of cutting opens little tears and/or widens
existing pores in the metal being cut, and that the reason carbon
tetrachloride is so effective is that it penetrates very well, and has a
lot of chlorine.

I assume that research continues, if only because the perplexing and *
counter-intuitive behavior interests people, especially university
professors.

*Some reactions are fast and it
could be that surface chemistry is involved. *Maybe lead-based cutting
fluids would be effective (if not for environmental/health problems).

I don't recall that there were any lead-based cutting fluids, even in
research. *Sulfur and chlorine rule. *

Except that metallic lead in steel yields a very machinable alloy.

I don't recall if fluorine works, but I would guess that it does not, or
there would be a lot of freon-based cutting fluids.

This book has a chapter on coolants and lubrication:
³Metal Cutting² by Edward Trent & Paul Wright:http://tinyurl.com/p2l94p
It says that a more effective place to direct cutting fluid is along
the flank of the cutting tool or from underneath the cut.

Yes, basically flood the area, top and bottom.

Modern high-speed machining centers almost run underwater they have such
large coolant flows.

Joe Gwinn- Hide quoted text -

- Show quoted text -

I found an inexpensive copy on Amazon and ordered it. It might be
over my head, but I'm curious. I imagine that controlling the
"transition temperature" (ductile/brittle phases) of the material is
also involved with coolant. Probably lots of science going on at that
little tip.