"Gummy" metal while cutting

Pcmaker

Pcmaker

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I made a part out of 1018 cold rolled yesterday. I was using a 1/4" HSS endmill to cut 2 slots. First slot went without any issues. I was doing around .030 each pass until I hit the total DoC of .170 and the length of the cut was at .600.

The second cut I decided to do all .170 in one pass. When I started feeding, the workpiece became "gummy" and I was hesitating to feed since it became harder to feed in, fearing of breaking my endmill.

I then decided to do much smaller DoC at around .010 per pass and even then, it was rather hard to feed as it was pushing out gummy metal to the side of the slot that I had to file later on.

I forgot to use cutting fluid on the first slot but it cut fine. I only remembered to put in cutting fluid on the second slot when I noticed the gumminess of the part.

Spindle RPM was around 1200 and I was feeding slowly.
 
Possibly you dulled the endmill the first time? Never cut steel dry is my motto. Also I would have lowered the speed a bit, say 750 or so
Are these USA endmills or imported-? Not that imports are automatically bad, but some are
 
markba633csi said:
Possibly you dulled the endmill the first time? Never cut steel dry is my motto. Also I would have lowered the speed a bit, say 750 or so
Are these USA endmills or imported-? Not that imports are automatically bad, but some are
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I agree, what you describe is exactly what happens as the endmill gets dull. In my limited experience what dulls the bits the quickest is the chips piling up and feeding back in. It also makes for a rough looking cut. I blow or brush the chips away as it goes as I've got nothing else to do :) I also find the quality of sharpening of all endmills to be scattered. I've gotten new and resharpened endmills that were not equally cutting on all the flutes and that made the ones that were cutting go dull real quick and causes a cascade failure.
 
Might be the cheap endmills. This is part of a set $17 and you get 1/8", 3/16", 1/4", and 3/8", 1/2" 4 flute HSS endmills
 
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Pcmaker said:
4 flute HSS endmills
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Slots take 2 flutes best. That way only one flute is engaged in the metal at one time. 4 Flutes means that at least 2 flutes are engaged, at once, one of them pushing the cutter sideways.
I've dispaired when I see two flute endmills called slotting drills, but I guess while it's appropriate, it's not RIGHT.

EDIT: correct typos
 
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For those saying .170 DoC was too much, what should have my DoC have been each pass?
 
I think a large part of the problem was re-cutting chips.The greater the DOC in a slot the greater the issue with chip evacuation. With the smaller DOC the size of chip you were re-cutting was smaller.

Pushing metal ahead of the cutter suggests a dull cutter.

Dark (high sulfur) cutting oil helps with gummy steel.
 
I know this seems like a lot of extra effort, but often times in steel it helps to make things as easy for the endmill as possible, for example, drill a series of holes a bit smaller than the width of your desired slot, then the majority of the metal has been removed and the final milling portion goes a lot easier and your endmill will live a lot longer
Of course with blind slots this isn't easy, especially if the slot is very shallow, but the technique still applies
 
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