[beanbag]

Today I was cutting a part with a bunch of slots, cut with a 3/16 end mill. Based on some comments I read on CNCZone, I tried a regular uncoated carbide 3 flute end mill. I was using 5000rpm, 18 ipm, .11 axial depth of cut. At some point, the end mill just blew up. I was kind of surprised, because that is barely more than .001 chip per tooth. Also, I was using air blast plus coolant dribble (splatter cooling?), so the chip clearing should have at least been ok. I finished the part using a 2 flute end mill and only 10 ipm.

Any ideas on what went wrong? Was 3 flute the right choice for slotting, and/or do I also need a high helix geometry?

[Steve Seebold]

What was the finish depth of the slot you were cutting? I have found that if your slot is too deep, then your spray coolant doesn't reach the bottom of the cutter and the chips will weld themselves to the flutes clogging them and breaking the end mill. I have learned that for the most part, spray coolant works really well on the outside of the part, but if you're pocketing or cutting deep slots, flood works best. For me anyway.

It could also be that you were a little too agressive on your depth of cut.

[tbaker2500]

I'd shallow up the depth of cut. I seem to find that shallower depths of cuts and higher feed rates gives me less troubles overall.

[Wog]

I plunge and slot 1/8" thick 6061 stacked 3 high with a 3/16" 2-flute Tin coated solid carbide EM with flood coolant. Depth of cut is the full 3/8", but smaller chips because of the 3 layers. Speed is 4500 (Series 1 1100) at 9 IPM. They seem to last forever. I think your 3-flute has too much deflection. I usually use a 3-flute in the 3/8" and larger EM range.

[kevinro]

Today I was cutting a part with a bunch of slots, cut with a 3/16 end mill. Based on some comments I read on CNCZone, I tried a regular uncoated carbide 3 flute end mill. I was using 5000rpm, 18 ipm, .11 axial depth of cut. At some point, the end mill just blew up. I was kind of surprised, because that is barely more than .001 chip per tooth. Also, I was using air blast plus coolant dribble (splatter cooling?), so the chip clearing should have at least been ok.

I was cutting with a similar bit, speeds and feeds except I was using flood cooling. Also had a bit break off when the coolant level dropped and I didn't get good flow for about 20 seconds. I was cutting full slot .20 deep with flood cooling, and it worked great.

Air blast/misting isn't great on a pocket or a slot. Remember the coolant isn't just for cooling, it is also a lubricant. If you aren't getting it to the bottom of the cut, then it isn't worth a lot!

[beanbag]

I noticed that even when I was cutting the first layer of the slot, there would be an occasional light crunch sound, and a small dent or burr in the surface finish. I assume this was a chip getting jammed. Because the air/coolant was only coming from one direction, there were some times when the direction of the spray was probably not optimal. However, even at the point when the cutter broke (.22 deep by then), it was still getting a splattering of coolant.

Is it more important to have a powerful blast of air to shoot the chips away, or a flood of coolant to drown the cutter? Since the slot is inside a pocket, the cutter will be immersed in a pool of coolant.

I often use a 2 flute 1/8 end mill to slot at .1 depth and 10 ipm with no problem - even when the coolant temporarily stops.

[beanbag]

Just wanted to update that I did the exact same cut at 5000rpm, 18 ipm, .11 axial depth of cut with a 2 flute instead of 3, and it seemed to work fine. My coolant flow was better this time, but I think the main thing was that the 3 flute didn't have enough chip evacuation capabilities. I think I will stick to using 3 flutes only in the bigger sizes like Wog said.