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.


I'd like to fill in the chart (my guesses shown):

Mild Cast Tool*
Steel Iron Steel Alum Brass

Lathe ? D ? ? D

Mill ? D ? ? D

Drill ? D ? K D
press

Band W D ? ? D
saw

C = coolant
L = lube
D = dry
K = kerosene or equiv
W = wax

* - actually I don't care about Tool Steel, as I never use it. It's
included for completeness

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