FYI: Milling hardened steel

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rashid11

Joined
Dec 8, 2005
Messages
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TiAlN coated carbide EMs eat it (~64RC) like butter. Hear voice of reason
and don't try to take off 1/8 in a single pass. The mill has to be rigid, as carbides
don't take too much play too lightly.


Now, before one sez - heck, I am sure some NASA outfit has solid diamond
EMs that can mill carbides, problem is it costs $100K per EM, Ebay has very
nice TiAln carbide EMs for .... UNDeR $20 for 1/2 4FL ! US made ! :thumbup:
 
Diamond coated end mills can be had for $200 bucks. For machining abrasive materials such as graphite, they last 10-100 times longer than carbide. You can't cut steel with them, the diamond (carbon) quickly dissolves into the steel.

Carbide end mills don't last real long in full hard steel, especially steels with carbides in them. Mold steels, such as P20, H13 and S7 are commonly milled while hard, but not 64 HRC.

So in short, you can do it, but don't expect your cutter to hold up a long time. Low SFM (such as 80 surface feet per minute), small depth of cut and normal feed per tooth will work. A lot of people do it with high feedrates and no coolant. Sparks fly, and surprizing, it is supposed to do that. However, that ain't regular carbide.

But like you said, Ebay has very nice TiAln carbide EMs for .... UNDeR $20 for 1/2 4FL ! US made. I use them, they're quite good.
 
What you find with carbide EMs, plain or coated, it is not loss of sharpness but chipping, that leads to EMs demise :)

One has to be alert working with them: if you hunt for workpiece's edge by
touching with EM's flute, approach it real nice and ez, while looking @ the gap
against some backlight. Turn EM's only CW - much like the reamers, the EM
will get destroyed if you, by mistake, turn it CCW.

If you probe in Z by touching the top surface of workpiece with the bottom of
EM, lower it nice and ez. Some old timers use a strip of paper of known thickness to look for edges.
 
Carbide end mills get dull just like any other tool. They also chip, break, degreade from friction, etc etc.

Don't use a cutting tool to find the part, use an edgefinder or better yet, a 3D probe.
 
Kev - whatcha doin' in Berlin, may I ask ? :)

Most of here don't abuse our tools to the same extent a production
shop would, so they tend to last a lot longer.
 
Well, for a number of years I've been a professional knifemaker!

I think you have a misconception about metal working professionals: tools are not abused; they are used. That's why we buy them. All machines and all cutters have a finite usable life, then they wear out. Misuse or mistakes cause early failure.

Many companies make special cutters for working hardened steel and these should be purchased for such applications.

Endmills will last forever if you don't ever use them; if you do, they won't.
 
Kevin,
thanks for the link. I guess 3D probe is only for CNC. I have only manual nachine.
P.S. Your knives(and setup) are fantastic!
 
You're welcome!

3D probes can be used the same on analog machines as on cnc machines! You just need to be able to mount a tool with a 20mm or shaft or buy the probe complete with holder (SK40 for example) that matches your spindle.

They are a giant timesaver and make accuracy easy.
 
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