annular cutters in 316?

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i tried to drill 13/16" holes in 3/8" 316 stainless the other day.Did 2.5 holes before the bit stopped cutting.the bit was used for @60 holes in steel and was still cutting fine.a mix of oil based lube and water @ 50%/50% was used for all holesI also tries to keep a good cutting speed (vertically) as i was aware of 316 work hardening with heat....and winning.is this typicalor was i screwing upG
Reply:I think stainless is a whole nother animal.  I've heard it's hard on tools.  I believe that cobalt is reccomended, and a much slower speed.  Around 50-90sfpm instead of around 100sfpm for regular steel.  I just thank God I never have to mess with it."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Here's this again.  It will give you a ballpark speedAnd don't take my comment on cobalt to the bank, I'm not sure Attached Images"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Not typical, cutting speed (SFM) should be lower for 316 than for mild steel- could be/probably the cause. There's a chart for suggested cutting speeds with different materials here and a calculator here
Reply:I like cobalt, then pure carbide drills for SS. With a sharp steel bit, you can cut it/ drill it pretty well, but the feed pressure has to be consistent. I find that I can get a lot of holes drilled with a single bit so long as I keep the pressure steady and pretty hard, and the speed low. Also, keeping the workpiece set still while you drill it helps immesurably. And for cutting oil, I use a heavy tapping oil. It seems to stick better, especially when I am hand drilling 90% of all holes in my ss work.And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.
Reply:I am sure you have discovered that if the cutter goes dull and starts "rubbing" the metal in the bottom of the hole the SS will work harden to the point that nothing short of a carbide cutter will restart the hole.  For that reason as soon as you notice the cutter having any sort of difficulty or the chips stop feeding out stop cutting immediately and put on a new cutter.  Rotate the dull cutters to a sharpening service regularly.   I would go at less then half the cutting speed for mild steel and keep a steady cut going.  So not take too light a cut.  Make sure you have a steady exit of chips coming from the hole, as Gordfraser mentioned.  Check the manufacturer's literature on your cutting fluid.  Several that I have used recommended a stronger solution/mix for stainless and alloy steels.  The worst part is when you have a hardened surface in the bottom of a hole.  I have had to turn the workpiece over and drill from the opposite side.  Even then as you break through the back side of the hardened area you are likely to chip or ruin the replacement cutter you just put in the machine.    If you have a lot of holes to do .... say more than ten, I would seriously consider at least high end cobalt cutters or better yet invest in carbide tipped cutters.  In one shop I worked in only the machinist was allowed to used the carbide tipped cutters.  They last forever when used correctly.  We were happy to let the machinist take the heat if he broke a carbide.... which he didn't.
Reply:just to inform anyone who searches for this thread.i got a 9/16" TIN (titanium nitrate...i think) annular cutter for my next 316 project and it cut well.so far it has 40 holes in 3/8 x 316 and is still going strong.got a mix of 50/50 oil based cutting fluid and H2O. got to keep shaking it up.as long as there is steam like smoke and not smoke like smoke it seems fine.this was the manufacturers recommendation.G