I did some grinding on my lathe some years ago. The stone was sitting
in a pool of oil - and I shook it 'dry'. Tool post grinder cut a nice
clean finish. Small grain showing. The stone naturally shot the oil
outward and got dry so when the other half of the work was ground (it
was in the jaws) - the measurement and even a fingernail ran over the
'edge' between grinding - both smooth but the grain showing was obvious.
The only difference was the oil that worked on the surface.

My take on the whole thing - not oil between but the working surface
isn't as hot with oil pouring over it - without it tends to tear due to
melting temp on the very edge due to heat. It makes for a rougher
surface than when cooled with a flood.

As far as the blocks I always thought it was atomic friction. The
surface is so fine that atoms touch. Rough surface allows only few to
touch.

Martin

On 12/2/2016 1:51 PM, wrote:
On Thu, 01 Dec 2016 23:30:10 -0500, Bob Engelhardt
wrote:

On 11/29/2016 10:17 PM, Gunner Asch wrote:

It flows on. It only takes a thou or two to float a chip

That seems reasonable, but:
- the stock is moving MUCH faster than the oil can flow (100 FPM = 20 in
per second). By the time that the oil starts to flow over the cut edge,
the tool is long gone.
- the tool is constantly cutting, so that the chip is in constant (high
pressure) contact with the tool face. How does the oil get between them?

This idea of putting oil on the stock is making less and less sense to
me. I'm beginning to think that it is done because it's always been done.

What makes sense is to put the oil on the tool before starting the cut.
Putting it on the tool during the cut _might_ work (if the oil could
somehow flow under the chip).

Bob
I have been machining metal for over 40 years and still don't quite
understand how the cutting oil on the stock gets between the tool and
the work. But it does as evidenced by improved finish of better chip
control or less chip welding and so on. However, directing high
pressure coolant right at the point where the cutting tool meets the
work is even more effective.
Eric