I recently bought an Eagle Rock scissors type knurling tool like this:
The catch is that the shank is 5/8" high, and my 11" lathe has an Aloris
AXA sized tool post on it, which can only take up to 1/2". No big deal I
figured, I'll just mill it down.
I hit it with a file, and it was pretty hard, so I used a nice new 4-
flute 1/2" Fette carbide end mill I had (note past tense). This has a
small (0.020") chamfer on it to avoid stress concentration in a sharp
corner. It's not under tons of stress, but it's what I had.
I have a Clausing 8520 mill, which is small, but a nice matchine if you
don't push it. The speed was set at 1000 rpm, which I figured would be
OK. Not wanting to push things, I took 0.015" deep passes, with ~ an
inch a minute feed. This all seemed to work OK, but after a number of
passes, I noticed the amount removed didn't look right compared to my
total Z-axis feed. I measured it, and I was about 30 thou shallower than
I figured, OK, the end mill is slipping in the collet. I took out the
end mill with the intention of cleaning it & trying again, but I noticed
that the lovely sharp edges of my end mill were no more. It had worn
down the cutting edge to a very noticeable degree.
I'm about 3/4 of the way down to where I need to be. Tomorrow, I can hit
the nearest MSC for another carbide end mill of some flavor. However,
before I trash another one, I'd love to know what the heck happened and
how to avoid it in the future.
There are two issues:
1) What the heck is this stuff?: At worst, I figured the shank might
have been case hardened. It's cut from bar/sheet stock, not cast. I
haven't taken a grinder to it because it's all set up in the mill, but I
suspect it must be pretty hard throughout.
2) Feeds & Speeds?: Am I babying the cutter & wearing it out? Work
hardening the material? What sort of depth, speed & feed should I use to
maximize tool life? I experimented with using cutting fluid (Mr. Cool
Tool II), and it didn't seem to make any difference, so I mostly cut dry.
Keep in mid that this ain't no Bridgeport, so I can't get too agressive.
Also, will the chamfer tend to make the end mill want to "climb" into my
This is the first time I have ever worn out a cutter (much less a carbide
cutter) is less than one job. It's annoying to trash an expensive end
mill, but more so if I don't learn something useful out of this (other
than don't try to cut mystery metal).
(If you are wondering what the heck Krell metal is, it's from the movie
"Fobidden Planet", and the stuff was nearly indestructable.)
Thanks for any suggestions.
- posted 10 years ago