Newbie- Do you ever use coolant when working in carbon steel?

[Driftwood]

I almost never do work in steel, mostly plastics (which I try to run dry), or aluminum and stainless steel (which I always run with flood coolant.)

So for those guys that do a lot of milling and/or turning in steels, from mild to tool steels, do you ever run with coolant? I understand you can run dry with steel if you want, but is that better/worse on tool life?

I ask because I'm probably going to be doing a big job in a high carbon steel soon, probably with indexable and coated carbide tooling...

One last question: tooling and insert suppliers recommend speeds and feeds, but rarely say if that's wet or dry machining. If its a steel grade, assume they mean for dry?

[Geof]

We do a lot of work in leaded steel and cold rolled and hot rolled C1018 and on the production stuff always use flood coolant with modest speeds and fairly good feeds.

Doing prototypes and fixtures when I am working with one offs and can take the time to get conditions correct I often machine dry with an air blast sometimes at very aggressive speeds and feeds.

The main reason I have never changed over to dry machining for our production stuff, even though it could possibly boost productivity, is that if something does go a bit haywire you can burn out a tool very quickly and because our production stuff runs on mini-pallet systems with the machines un-attended you finish up wiping out a whole lot of tools. Sometimes it is better to be conservative.

[cjjonesarmory]

Definitely run coolant. It will extend tool life by flushing out chips and swarf, and it will keep the cutter cool.

The only ferrous metal I cut without coolant is cast iron, which can "work harden" if coolant is used. I recommend Rustlick WS-5050, but WS-11 will work also. The WS-5050 uses extreme pressure additives and is chlorinated, the WS-11 is basic water soluble oil without extra additives.

Typically speeds and feeds are rated for dry, with HSS tooling. Using coolant you can increase speeds and feeds by 10% (over dry HSS). With carbide tooling, you can supposedly increase speed and feed up to 100%, but really depends on the application.

[little bubba]

Driftwood, first, its not that you can run dry, but why? and to what advantage?

I'll give you 3 points, relating to carbide, with HSS, wet is going to be better 99% of the time.

1st) Thermal shock, carbide can take heat and lots and lots and lots of heat, what it can't take is continual rapid changes in temperature. When cutting you are generating MASSIVE amounts of heat that can easily reach well over 2000F. These huge temperatures are localized with the highest temps occurring just behind your cutting edge. So lets say you are milling at a very slow sane speed of 600rpms, and running wet, that piece of carbide is doing a thermal cycle 10 times a second, a 1000+ degree fluctuation 10 times a second, its not going to be happy.

2nd) So, we've determined that carbide doesn't like heat cycling, so coolant is bad in a situation where there is an interrupted cut, not always so. The problem with coolant is that 99% of us do not posses the equipment to get the coolant where it needs to be when it needs to be there. It needs to be between the metal and the cutter that is creating massive heat. That requires high pressure to break into the inevitable steam pocket created and some way to make sure that the coolant is directed at the actual cutting point, not so easy with a spinning cutter that is trying to throw the coolant away from it.

3rd) coatings, we've got these new fancy high fangled coatings, and they come into play at high temps. Most variflutes come with a TiAlN, or AlTiN coating, this guy comes into play at a very high temp, around 1700 degrees. At those temps it gets real hard and real slippery. Below that its pretty useless and soft, and the carbide underneath it is usually softer and tougher than you would get with an uncoated endmill. Running wet with these guys just negates all the good stuff you paid a lot of money for.

So, milling, I run dry most of the time in pretty much any steel, and let it fly. I also run dry in 303 and heat treated 17-4, annealed(solution treated) 17-4 is just too damn gummy to run dry.

On a lathe, you don't have an interrupted cut, so heat can build, in that case, wet to control your temps, though I will run dry when knocking down a hex and then go wet when I get into a continuous cut.