I'd like to point out that you guys are comparing two extremes: TPG's are old-school inserts with no surface features (no chipbreaker to optimize the rake angles). To make matters worse, the cheaper TPG facemills have the inserts laying flat in the pocket (no radial rake) so they slap the workpiece and hammer the spindle. But they've been around for 30 years, so you can literally buy name-brand TPG's for 25 - 50 cents each.
Originally Posted by PaulT
The APKT's, by contrast, were until recently the latest and greatest inserts: they have a helical twist molded into the insert, and with a good mill body, they're just about optimal for surface finish on low power, low rigidity machines. But the inserts are $7 - $11 each at CarbideDepot, and $15 - $20 each retail (!)
I love my APKT facemill, but I get nervous when I load it up with 6 inserts @ $7 each...
But a good compromise that a HSM'er might consider is an SEHW "shear mill". It's a square insert turned on it's edge (45° lead angle) with a modern chipbreaker shape in a facemill pocket with steep axial and radial rake that gives the insert a high positive cutting rake angle -- very low horsepower and rigidity requirements. You can find Kennametal KSSR facemills which use these inserts for dirt cheap on Ebay ($50 - $90), Bison and Dolfa (same company?) sell them inexpensively at Penn Tool, and the inserts themselves sell for $2 - $4 depending on the grade and coating.
The inserts on the top row are SEHW's. The top-right is has an extreme positive rake and is razor sharp, for finishing aluminum. The bottom middle is a Sandvik's RA-245 -- their proprietary version of the SEHW inserts with a more sophisticated chipbreaker and a carbide anvil for crash protection:
Last edited by lazlo; 02-14-2010 at 11:52 AM.
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