Carbide End Mill Insight

Hey everyone, I’m making some axle flanges on the MR-1 out of some 1" thick mild steel block. I probably didn’t need to use something that thick, but its what I had laying around. Op 1 I cut the flange out, Op 2 I flip the part and face what I don’t need which is around .350". I’m facing with a 1/2" 4 flute carbide tool. KBC part #4-326-032. Once the program was nearing the end you could hear the end mill had started to loose its edge, didn’t sound right. Finished the program and this is what it looks like. I’ am kinda new to cnc milling, but shouldn’t this tool last longer? Cut settings were 5300RPM, 40 in/min, .400 step over, .220 max step down. Any insight is greatly appreciated! Thanks.

.4 step over might be a bit much for 40 ipm. I do .25 @ 35 ipm and haven’t ruined an end mill yet. Only done a couple of steel parts though so far.

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At 5300 RPM with a 1/2" End Mill, that’s right at 700 SFM. (693) That seems rather high for mild steel. I found for my 1/2" Accupro 4 flute carbide they recommend 360 - 400 SFM. For 1/2" that equates to 3050 RPM and 22 IPM.

As far as stepover, half your tool diameter is a good starting point.

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It looks like chatter? How are you holding down the stock? Your part may be vibrating.
I also agree that 25 - 30 ipm is a good starting point.
I would cut that stepdown in half. Almost a 1/4 inch at a time in steel is alot.

Holding stock in a vice, about .300" work holding. Oops, thats suppose to be .022" max step down.

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Ahh ok, Ill slow everything down and try it again. Thanks!

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Running coolant or dry?

.400 step over is a lot for a 1/2” endmill. Look up HSM (high speed machining) techniques for better finish, material removal rate, and tool lifespan. With HSM you normally have a step over of about 20-30%, but a deeper depth of cut. This uses more of the cutting edge of the mill at one time.

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Step over and IPM usually not a huge concern as long as machine can handle it, RPM is typically your main issue with end mill life (unless you are feeding hard enough to break it) Slow down the RPM, in steel with an HSS endmill the chips should not get any hotter than a light yellow. and with carbide you should shoot for dark blue as the hottest. light blue means you are pushing it. This is with the coolant turned off momentarily to check temps. If your stock was flame cut or had welds on it, the thick flashing and some welds can be particularly hard and damage endmills. If its flame cut id highly recommend grinding off all flash before machining. And if it’s welded on may want to start at high alloy SFMS.

If your work piece was loose or it was chattering it can also chip endmills, but that endmill looks like it got burnt up from rpm or something hard.

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Recommend running the settings we have in the cut chart. They work!


I used the Langmuir settings and ate 2 cobalt tools in about 10 mins of machine time.

Using Langmuirs settings thier Tialn end mill lasted 1.5 hours machine time.

all tooling was cutting the same stock.