Coolant or not on steel?

Been using coolant on my SL3 machining prehard 4140 and annealed K245 with success.

Aluminium i know coolant is a necessity.

What about milling steels?
While i wait for my Robodrill to arrive i have been busy getting programs for it ready.
Milling pre hard 4140, and as delivered soft condition S7, K245, 01 etc. what the general thought on coolant? using soluble oil. Cut dry or wet?

Cheers

Simple answer is: Look at your chips. If dark blue, no coolant (sudden chilling of cutting edge will dull tool). If chips are not dark blue, you can safely use coolant. I like coolant, it washes chips away and actually lets me feed quite a bit faster.

Probably should ask - coolant or air blast.

I would not run nothing (except maybe a BP or sumthin'), usually coolant is *ok* for solid carbide endmills, but would run air blast on insert cutters and when machining hardened materials.

* check manufactures recommendations.

Chip color isn't as important as having two colors. That simply means the chip can take more heat away if it needs to.

Typically doing 70% stepover with an EM you'll see white and yellow at first, then yellow and blue, then blue and black, and finally just black. Once the chip is just one color you have used about 60-75% of the tool's life IME.

Carbide can take HEAT.. LOTS and LOTS of heat. And it doesn't care.

What carbide does not do well is rapid thermal cycling. If you are running
coolant, and its not getting right where it needs to be, when it needs to be
there, you are heat cycling that carbide 1000's of times a minute.

My general rule of thumb. Mild steel, or annealed alloy steels. 300sfm is
my cut off. Below that I can run wet, above that.. Turn the coolant off,
and then the sky's the limit.

Also think about your coating. The purple stuff. TiAlN or AlTiN doesn't
start working its magic until it gets HOT!!! really HOT!!! 1400 or 1700
degrees, somewhere in there, hotter than you would cook a chicken pot pie.
Thats when it gets hard, and it gets slippery as snot.

Stainless's, depends on your technique. 300series, I'm always wet, though
I know you can play dry on occasion. 17-4 especially heat treated can go dry.
13-8 always wet. and I've probably only machined a pound of 400 series in my
life, so I have no idea.

Ti, wet.

aluminum. You can go dry, even in 6061, but your technique has to be spot on,
and the heat HAS to go out with the chip. Here is a video I made a while back,
6061, if I ran it wet, the inserts broke down. The trick was heat out with the
chip. 2000sfm, and .020+ per tooth.


Here is the same tool doing the same thing, from the same guy I got it from, and
helped me figure it out.

I didnt think there would be a simple answer!

I will only be using endmills, not insert cutters. 99% of what i make in steels are only a couple of inches long at the most. I can do air blast if needed. Not making 10,000 parts a month either.

Thanks!

I almost always use coolant. Save for plastics or certain materials that may stain. I used to run full synthetics, but I've re-discovered water soluble and prefer it.

I like to go dry as long as Im able to get chips out of the way with air blast.