Too fast or too slow?

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walterwoj

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So I was just cutting a slot in a piece of 4140 steel. DOC was .380" rpm was 2170 (max mill speed) according to the little machine shop calculator my ipm SHOULD be 33, I figure I was going closer to 2 ipm. I made it 75% through the cut with a carbide 1/2” roughing endmill (Chinese) before it burned the corners off the endmill (the sides look good still) so my question is: was I going to fast or too slow?
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Chinese end mill possibly . A HSS cobalt rougher would have been my go to tool for that .
 
I now use radiused end mills because I lose too many corners. They do better. A rougher would be my choice as well. The .380 in one pass is a good bite... I would probably have done it in 2 passes on a bp.
 
Too slow, causing rubbing and dulling the corners, leading to overheating?
 
If you cannot run fast enough feed you need to reduce the rpm until it gives you the proper feed per tooth. You rubbed the cutter to death. It needs to always take a cut. I usually run 0.003 to 0.005" per tooth.

You were at 0.0002' per tooth. Not enough to maintain a cut.
 
Recommended 33. Actual 2. I’m going with…............... too slow. ;)

Tom
 
I don't think I understand the whole feed per tooth deal. It's prolly just me but while I think my power feed could do closer to 30 ipm I would never dare go that fast, the table would be flying! I can't help but think that if anything went wrong I would have something embedded in my face!

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Feeding that slow, and in a deep groove; you were likely recutting chips big time. Put a blast of air on it, and get those chips out of there.
 
walterwoj said:
I don't think I understand the whole feed per tooth deal. It's prolly just me but while I think my power feed could do closer to 30 ipm I would never dare go that fast, the table would be flying! I can't help but think that if anything went wrong I would have something embedded in my face!

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Click to expand...
Think of it as how thick a chip you make. Every time a cutting edge comes into contact with the work, it sweeps an arc through it. The difference between the last arc from the last edge becomes the thickness of the chip, or feed/tooth. Looking at the chips, you were feeding way, way too slow for that RPM. Good eye protection, arrange the work so you're flying chips away from you and get a bit braver with that feed :) It's most satisfying!
Another thing worth mentioning: tools steels, stainless and suchlike harden when rubbed as it generates heat which isn't removed with chips. This will give the cutter an even harder time, which I wouldn't put past being the case here.
As mentioned, carbide is not at all tolerant of cutting chips as it tends to cause fractures. Air blast to remove makes a world of difference.
 
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