indexable end mill question

[lazlo]

I agree 100% with PixMan on this issue. I get much better performance, tool life and quality of cut with APKT based endmills than I did with my original TPG based ones, so although the APKT inserts cost a little more they are cheaper in the long run.

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.

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:

[PixMan]

I have a 2.5" 45° high-shear mill also, I think it's a Widia. What a huge difference in the loads on dad's 1HP Bridgeport. Can a machine like that use all of what the cutter can do? Not a chance, but as lazlo mentioned, it is SO much easier on the spindle bearings. Cuts really smooth.

Mcruff, I am not disagreeing with you one bit, and in no way am I suggesting that you have a problem with trashing milling bodies. If you owned or supervised a shop you know I'm just bemoaning the lower-skilled people who don't respect what tooling really costs. Those are the guys who don't have a home shop!

I do see the value of using TPG inserts for some tasks in the home shop because of the price, but they're not a very rugged geometry. You have been around long enough that you know how to use them on both lathe and mill applications successfully. Many a novice would try to use them too aggressively as their first inserted carbide tool, trash the inserts and the cutter and form an opinion that carbide tooling just isn't worth the money.

Making the situation worse for TPG inserts is the issue of milling grades vs. turning grades. While you can't use an APKT or SEHN insert on a lathe, TPG's have holders for both types of machine. For some applications, such as a C-2 uncoated grade used for turning cast iron, no problem. Try milling with a C-6 carbide with too much feed and you soon have two-piece inserts.

For me, I've shopped carefully (and been given a few good gifts) for the home shop and feel dad & I have the optimum tools for the way we work. He's more inclined to use a reground HSS end mill before the inserted carbide, I'm the opposite.