# Modify Arbor for Free Shell Mill



## epanzella (Mar 4, 2022)

A friend was cleaning out an area in his shop where an old machinist used to reside before the work was outsourced. He called me and said "help yourself". I got a 6 inch Bridgeport brand vice, a cupla dozen R8 colletts, various die holders, and some shell mills. I also scored over a hundred pounds of drill bits and reamers up to 2 inch. It was all kinda grody looking but it's cleaning up nice. There were two nice 3 inch shell mills (straight and 45degrees) with arbors and a 2 inch that had no arbor that fit it. I did have an extra arbor that was too big to fit that last cutter so I decided to machine it down to fit. I pressed out the 2 locating pins then attempted to machine the hardened core and threaded retaining piece down with a 60 degree carbide insert. Despite taking light cuts (a file slid right off) the first insert literally disintegrated on my second pass with associated flames and fireworks.  I had nothing to lose so I broke out my trusty CNMG tank buster. I was able to take 20 thou passes and got a nice fit on the bore of the cutter. The outer retaining piece was hardened also but I got it turned down ok. The inner shank was too long but I was afraid to shorten the hardened threads and possibly ruin the part so I made a mild steel spacer. It's done now and runs nice and true. My first hard turning and I'm a happy camper.


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## Chris Hamel (Mar 5, 2022)

Call me stupid but I'm not familiar with CNMG.  Can you enlighten?


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## epanzella (Mar 5, 2022)

Chris Hamel said:


> Call me stupid but I'm not familiar with CNMG.  Can you enlighten?


It's an almost square 80 degree carbide insert. Kinda boxy for getting into tight spaces but very tuff.








						ISCAR 5507754 - CNMG432-TF IC8250, 80° Diamond, Indexable Carbide Turning / Boring Insert
					

Features80° Diamond Shaped Indexable Inserts.Versatile and dependable, "C" shaped inserts are one of the most popular shapes in the industry.Negative inserts can provide up to 8 cutting edges, four 80° cutting edges and four 100° cutting edges (seperate holder needed to utilize 100° cutting...




					www.travers.com


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## Chris Hamel (Mar 6, 2022)

Thx


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