Making chips - Close up

Fascinating!

-- Doctors prescribe medicine of which they know little, to cure diseases of which they know less, in human beings of which they know nothing.

--Francois-Marie Arouet Voltaire, about 250 years ago

Very educational. What type of distance of travel were we looking at there? It seemed like in all cuts it would build up a wedge of garbage on the cutting edge and then eventually roll it under or deflect the cutter creating a larger imperfection in the surface. For finer finishes would that mean atleast in cnc you could use a form of peck turning? Its hard to gage in that video, but the distance between the more substantial imperfections seems quite short.

Regardless, very entertaining.

Thank you. Bob La Londe

That pattern was first observed at Carnegie-Mellon Univ. in the 1950s, and by Dr. Eugene Merchant at Cincinnati Milicron. This video is much better than the films they made, showing close-up at high resolution how the compression-failure/shear-failure mechanism works.

In very fine cuts, it's mostly shear. At deeper cuts, it's often compression failure, then shear. In some materials it's mostly shear even with deep cuts.

Some of the interesting work they did was taking spark photos of ultra-high-speed machining (over 10,000 sfm). For that, they shot a .30 cal. bullet across the edge of a cutting tool. The failure mechanism for that is extrusion/shear, and cutting forces per cubic inch of metal removal actually go down. The chips are much longer than the path of the cutter in the material, with the chip extruding far ahead of the cut.

Neat!

Makes me wonder -what is the point of sharpening the tool? The cutting edge appears not to be doing much actual cutting.

MikeB

"Bob La Londe" fired this volley in news:IitBr.5700 $ snipped-for-privacy@newsfe05.iad:

That's called "a false edge", Bob. It happens to all tools; more without proper coolant/lubricant.

Dija notice that the T.I.N. HSS bit cut _very_ cleanly for a little while, then the metal started to adhere to the rake, and started stuffing-up?

That happens, too, for the same reasons as above.

LLoyd

Importance of a chip breaker on the insert.

The difference in coatings was impressive also.

Mart>

I was thinking of a dull table knife pushing thru chocolate.. or a road grader pushing up packed dirt. A lot of cutting is more of a scraping process, and that leads me to believe that cutting lubricants are definitely a major benefit, in many ways.

I have a difficult time recognizing that a negative rake cutting edge is an effective method of removing metal, but it's a commonly used process/method.

The popular TiN coatings don't actually make cutting edges sharper, instead, the coatings are intended to aid in chip evacuation, as black oxide can also make a surface slicker.