Is it the end mill or the machinist??

When looking at the chip load for mild steel using a carbide cutter, I usually see 0.001" for a 1/4" carbide end mill. SFM range anywhere from approximately 50-250, using 200 which may be a bit on the high side if harder material, you get an RPM of 3000 with 12 IPM, if 150 then 2300 RPM with 9 IPM. I only do manual milling, but use a power feed and set the IPM off of the DRO. With steel I use 4 flute carbide and cobalt end mills usually with some cutting oil, with a full size knee mill I usually end up milling at 1/2 the rated SFM, and usually a bit lower on the RPM. You might be a bit too aggressive in your milling parameters.
 
I will just have to try the slots again with a slower feed. No big deal, I am not running production here.

So, with that being said, could the chip loads safely go up if the diameter of the end mill went up as well? Like a 1/2" or 3/4" end mill? This reminds me of when I used a little 1/16" 4 flute carbide end mill on some aluminum a while back. a 0.0005 chip load caused it to break within about 5 minutes of use. I had to back the feed down to about 0.0002 chip load and the second end mill survived the whole cycle.
 
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Jake2465 said:
I will just have to try the slots again with a slower feed. No big deal, I am not running production here.

So, with that being said, could the chip loads safely go up if the diameter of the end mill went up as well? Like a 1/2" or 3/4" end mill? This reminds me of when I used a little 1/16" 4 flute carbide end mill on some aluminum a while back. a 0.0005 chip load caused it to break within about 5 minutes of use. I had to back the feed down to about 0.0002 chip load and the second end mill survived the whole cycle.
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Yep! Bigger the end mill, bigger the chip load.
 
When you run a 4 flute vs. a 2 flute cutter, you're basically doubling the speed of the cutter while taking off 1/2 the amount of stock. 3000 RPM is way too fast to cut any steel. If you want to hog a part, consider back gears with a faster feed.
 
4ssss said:
When you run a 4 flute vs. a 2 flute cutter, you're basically doubling the speed of the cutter while taking off 1/2 the amount of stock.
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With the same speed and feed, a 4 flute cutter will take twice as many cuts per revolution as a 2 flute, resulting in half the depth of cut per flute. Nothing else changes. As a side effect of the cutter shapes, chip clearing may not be as good with the 4 flute and tool rigidity and strength will less with the 2 flute.
 
If rigidity is not an issue I'd guess either re-cutting chips or material pickup on the flutes could be causing the problem, flood or air plus lube might make a difference,
Regards,
Nick
 
Sounds like you figured it out. I have a small cnc mill and I wouldn't run that chip load and cut speed. The cost of good end mills usually makes me error toward the conservative side and have the job take a little longer. I don't do production either so usualy in no rush but then again it's been a while since I've broken an end mill which I save for programming blunders and user error.
 
Bob Korves said:
With the same speed and feed, a 4 flute cutter will take twice as many cuts per revolution as a 2 flute, resulting in half the depth of cut per flute. Nothing else changes. As a side effect of the cutter shapes, chip clearing may not be as good with the 4 flute and tool rigidity and strength will less with the 2 flute.
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I think that's what I said but in English
 
Are the end mills center cutting?
If not could be part of the problem
 
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