90 degree indexable shoulder mill troubleshooting

So I bought an Accusize / Northward 1" R8 90 degree indexable end mill a while ago. It came with 2 general purpose APKT inserts. It looks pretty well made for the price. I faced some steel with it and it did the job nicely. I bought some APKT inserts for aluminum, and again, facing aluminum with these it works pretty darn well.

Today I tried milling the ends of some aluminum. Here's what I got with a cheap 5/8 HSS-AL 4-flute end mill. Pretty much right on.

Here's the indexable face mill, steel inserts. Close to 90 degrees, not perfect.

Here's with aluminum inserts. Way off.


So what is going on here, is this end mill only meant to be used with a particular set of inserts?

Here's the end mill in question:
It almost looks like the difference in the cutting edge (or chip breaker?) is the culprit. The steel insert is raised slightly at the leading edge, I guess due to the chip breaker design. The end mill has the insert at a bit of a shear angle it looks like, so that might account for the results I'm getting.



But that would seem to defeat the purpose of an insert end mill. If it doesn't cut 90 degrees if a different (yet seemingly compatible) insert is used, no?

Tool angles:
Cutting rake angle: 11° to 13°
Radial rake angle: 11° to 13°
Axial rake angle: 6° to 10°
Setting angle: 90°

Accusize web site indicates that has a >91 degree angle (see photo). The insert rake, plus chip breaker geometry, means you aren't going to get exactly 90 degrees.

I'd put an indicator on the insert edge and run the head up and down. You'll have to rotate the spindle to ensure the edge stays in contact since it's tilted back 11 to 13 degrees, but you should find that the actual angle at the workpiece interface isn't really 90.

You can try different inserts, or you can call Accusize and ask them if this appears to be a defect or part of the design. They may have recommended insert brands or designations within the APKT family known to work better.

Or you can consider this tool a rougher and just finish up with a solid end mill.

When face milling against a shoulder, we recommend a 90-degree milling edge to allow close proximity to the shoulder and to minimize the corner radius left in the wall/floor transition.

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