On Friday, December 2, 2016 at 2:47:47 PM UTC-5, 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

You're not alone. No one understands it. g It's been studied since the 1920s. There was a lot of research going on in the 1970s. Results were somewhat contradictory -- some studies showed an extremely fast capillary action that draws the fluid in, and others did not.

A few things are known. The edge of the cutting-edge/workpiece interface (the periphery of a bar turned on a lathe, for example) sets up the behavior of the tool in the cut. When that outer edge of the cut is lubricated, the whole cut surface tends to be cleaner.

It's also true that oil lubricates the chip as it flows over the tool, reducing the compression load right at the cutting edge. That may contribute to better finishes.

Some researchers have gone to great lengths to figure this out, including the use of completely clear "tools" made of aluminum oxide, and high-speed photography. Still, the results were not really conclusive.

BTW, there are quite a few phenomena in metalworking that are not completely understood. For another example, no one knows why gage blocks wring. Forget what you may have heard -- I've spent hours interviewing the world's top experts on the subject. They just don't know.

--
Ed Huntress