Are Tiny End Mills Impossible to Use in Steel?

Hi speed air spindles can be your friend. Have much lower runout than most spindles which reduces the erratic loading that kills tiny end mills.

Slitting saw would be more likely available to most. Cut down the center and follow with end mill to skim on each side one at a time to get to finish size. Air blast to clear the chips and cool the tool.
Pierre
 
I am not a very experienced machinist at all, but a .050” DOC in steel would not go very well on my small benchtop PM-25MV. I usually limit myself to .020” to .025” at the most. You obviously have a larger mill than I do.

The one time that I attempted to take a DOC that deep (which was in an ER70S-6 weld bead (which is very strong at 78 kpsi), the tool stalled and I had to hit the emergency stop. So now I just take lighter cuts, and that has been working fine for me.
 
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Did some quick calculations, assuming 100 FPM with mild steel and a HSS tool and a .125" 2 flute end mill and a feed of .0003 per tooth gives 3056 RPM and 3 IPM feed rate. Double that feed rate for a 4 tooth. I wouldn't even atempt that slow of a feed rate without a power feed. One slip and "ping" as you've found. Also, at that size, tool runnout becomes an issue. .0005 runout doesn't mean much with a 1/2" tool taking a .003 per tooth, but when the runout is larger than your cut/tooth that means you esentialy have a single tooth cutter, which halves your required feed rate. Anyone interested in hand cranking at 1.5 IPM? My eye is twitching just thinking about it.
 
Small end mills work fine in steel with enough RPMs. You need low runout and a fairly rigid machine.

This key fob is aluminum, but the inside corners on the drawers and the cloud were done with a 1/16" endmill at 10k RPM on a CNC Taig mill.
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Reading all these responses and averaging things out, it sounds like anything smaller than 3/16" is going to be very difficult to use in steel.

My mill is a full-size knee mill, so it's rigid, and I was running it at the correct speed. As for the feed rate, I can only guess at that. I went as slow as the power feed would allow.

I do have a slitting saw, but I refused to be intimidated into using it. I told myself that if I was going to buy small end mills, I was going to use them and see what happened. The temptation to baby tools can be a real problem. If I have something on hand, I intend to use it instead of hiding it in a drawer until I die. I guess what I learned was worth losing five dollars' worth of end mills.
 
I’d use a slitting saw and then if need be, clean it up with the end mil. My mill drill had a decent amount of wear so whenever doing a tricky job like that, I usually snug up the gib locks. Not tight, just a light snug.
 
for slotting I find that small end mills can start to wander a little bit if the DOC is too high. You can tell as when you reverse the cut it will cut on the other side of the slot. If that happens I'LL take a shallower DOC and do more passes until it's full depth, then clean up the sides.

The smallest I've used is 1mm in alu and that was terrifying, especially as I only had one of them!
 
Had to make a cut in a steel die. the slot was .490 inch deep x .063 wide x 1.500 long, there was no room for the run out of a saw, it had to be done with a 1/16 end mill with a 1/2 inch length of cut. these are real fragile and expensive. All 4 slots were cut without breaking a cutter, although a new cutter was used for each of the 4 slots. Depth of cut was .001, RPM was maxed out at 3200, feed was as slow as possible. Each slot took a full day to cut.
Your breaking small end mills had noting to do with rigidity. .050 was to much of a cut to try with that small of a cutter. Slow and easy gets it done.
 
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