Re: Speaking of round inserts....

Proctologically Violated©® wrote:
Awl --

It seems to me not of people use these, as I rarely see them in a shop's tool holders/racks.

Seems to me they would offer the most economy ito total cutting edge, and are geometrically simpler than anything else. And thus would be a mainstay in the job shop.

Do they have a more specific use?


The problem with round inserts for general purpose turning is that they make the widest chip possible for any given depth of cut. That means really, REALLY nasty chips that are difficult to break. To overcome that, you need awesome feedrates, which means you need extremely rigid machines, setups, workpieces, etc. Most folks just say "screw it" and use an 80 degree diamond.

But when the application is just right, round inserts can do amazing things. I once worked with a customer on a challenging turning project. Think of a 10" diameter disc, 2" thick, with about a 2 degree dish running from the OD to almost center. Then put a circle of 8 holes in the face, roughly half way between the center and the OD, and each just over an inch in diameter. Now make it out of a nasty alloy steel, and heat treat it into the mid 50's C scale. Now put a spec on it that says the dish/cone shape has to be right within about a thousandth, and have a 32 max finish.

Grinding this thing would have cost more than you might believe, so we (mostly the customer; but I got to watch and help) tried hard turning with round inserts. 3/4" round inserts, ceramic, on a nice beefy machine (Mori SL6 or 65). It worked perfectly, even across the interruptions where the 1" holes were. It was so much faster and cheaper than grinding, and so much better to have full control of this critical part of the job in house, that the customer got all of the production for this job, which had previously been split up among four shops. He ran bunches of them, and made a LOT of money.

KG

.

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