Re: Coolant vs. cutting oil/lube
- From: Joseph Gwinn <joegwinn@xxxxxxxxxxx>
- Date: Sun, 28 Jun 2009 10:20:06 -0400
In article <4a468a3e$0$31269$607ed4bc@xxxxxx>,
"Ed Huntress" <huntres23@xxxxxxxxxxxxx> wrote:
"Joseph Gwinn" <joegwinn@xxxxxxxxxxx> wrote in message
"Denis G." <guillemd@xxxxxxx> wrote:
On Jun 26, 3:14 pm, Joseph Gwinn <joegw...@xxxxxxxxxxx> wrote:[snip]
In article <h230t502...@xxxxxxxxxxxxxxxxx>,
Bob Engelhardt <bobengelha...@xxxxxxxxxxx> wrote:
Joe's recent thread about his dribble cooling for his lathe reminds
of questions that I have.
1. What is the purpose of cooling? Does the tool get so hot without
that the edge is dulled? I thought HSS & especially carbide could
the temperatures created by HSM work.
The first purpose of cooling is primarily to prevent welding of chips
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.
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 -
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
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.
When you get into really high-speed cutting, Joe, they often run dry -- or
with a 1/2-liter per 24 hour lean oil (vegetable) mist.
Yeah, that's now true, at least for the 40000 rpm spindle folks.
Most of the machining centers I've seen use a flood though.
BTW, I had lunch with Milton Shaw, back in the mid-'70s. We used his work
for several technical articles at _American Machinist_, 'way back when.
So he was the guru he seems to be.
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