I managed to break one of the flutes off of the 3/8" 4-flute end mill. I’m ordering a replacement that should come in September 20 - 26. Apologies for the inconvenience!
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I wouldn’t have worried about replacing the end mill. As I said in class, it’s a low end set, with more sizes than are generally needed. I am curious how you broke it. That probably means your cut was too aggressive in either size or speed, or your RPM choice was off, or you needed more lubricant. What type of cut was it (face, end, plunge, slot)?
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I was facing a piece of scrap steel square pipe with the following configuration:
- L2 rotary speed setting
- Removing 150-200 mils each pass
- Close to lowest X speed setting
- Applying lubricant each pass
Those settings seemed to be working okay, though I would be curious to know what you thought. I was trying to completely remove one of the sides of the pipe, but the steel on that face got so thin that it started bowing up and it caught and broke the bit.
In retrospect, I’m realizing that I should have first tried to remove as much material as possible using the vertical bandsaw, and maybe that particular type of cut wasn’t appropriate to achieve what I was trying to do. Next time I’ll be more careful with steel and ask y’all’s opinion before trying something like that.
That is WAY too deep a cut! 
By about a factor of ten!
20 thousandths (0.020”) would be a large but still reasonable cut depth for mild steel.
(Also, L2 might be a bit slow for a 3/8” end mill.)
Now that I think about it more carefully, 150-200 mils would have been about the thickness of the metal I was cutting, so I think I actually meant 15-20 thousandths. Apologies for the confusion.
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OK, that sounds much better!
Then the issue might be the RPMs. For something that small, I’d use at least L3, maybe even H1. Otherwise, the issue is probably that these are junk end mills. 
We do have a facing tool for steel that might have done what you needed too.
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I appreciate the advice, @mgmoore; next time I’ll try L3 or H1 for mild steel. I apologize again if I gave you a mild heart attack with my error in units. I don’t want to give you the idea that I’m going hog-wild and tearing up the community’s machine.
Is this is the facing tool we used in class that is shared with Tormach users?
I replaced the 3/8" 4-flute end mill, you can find it with the other Accusize end mills. Marking this thread as resolved.
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