Its a good post Timo but there is one omission concerning us modelers. In general we don't use exotic inserts or high load deep cuts and our materials are limited - if indeed we know what grade they are. So given that, and returning to coolants, can we say what is the best approach?
Full disclosure - I am only using pumped or brushed cutting oil for everything!
Mike
Hi Mike,
Pretty much all the different ways for cooling, lubing, clearing the cutting area do the same things from a high level. Remove the chips from the work area, improve surface finish, prolong tool life, and improve as machined accuracy of parts by providing thermal stability. In a lot of cases, as much as 80 percent of the heat is removed by cutting feeds and speeds making chips that take the heat away as they fly away or are blown / washed off. Or so Sandvik and other folks who should know have said. Removing chips avoids recutting of swarf. If you are recutting chips, you get lower finish quality, excessive tool wear, and lower dimensional accuracy. In the home shop, if the part is hot to the touch and we care about holding a close dimension, we can just wait a few minutes for it to cool off, check dimensions, and take our final pass or passes to get it right. In manufacturing, you rough hard and fast then do a final pass for dimensional accuracy and finish quality. Water soluble oil coolants tend to be used in high volume and pressure on larger work pieces, like CNC mills. Wimpy little "flood coolant" setups often seen on homebrew CNC machines just make piles of coolant soaked chips that you still have to brush clear to avoid recutting. MQL or mist coolant devices tend to provide some cutting and cooling action, but the air blast is hopefully clearing chips from the working area. Screw machines, AKA Swiss lathes like those from Tornos, tend to use pure oil as the nature of chip formation and cutter setup and forces is quite different from those in mills, and the parts they are used for also are difficult and costly for any finish cleanup operations after machining. Ever tried to polish the threads on a 0-80 screw? Now consider making thousands at a time. Better to have perfect threads and screw heads off the machine.
My defaults are kerosene (paraffin in the UK) for aluminum, sometimes isopropyl alcohol for very fine intricate cuts. Heavy thread cutting oil or Vipers Venom cutting oils for steel. Pretty much any smelly cutting oil that's thick. Brushed on is the most used method of applying.
I can run a mist coolant setup on CNC stuff, set to be fairly wet to avoid too much crud in the air. I really should build a nice little MQL setup I guess. Quite often on the little Sherline CNC machine I run just an air blast to remove chips and avoid recutting, particularly in brass when using quite small cutters.
Exotic inserts are sort of a user defined concept. To me a $10 insert is not unusual, but a $40 PCD insert would be. I'd use one if hard material cutting was needed for a job, but then it's not exotic, it's just the right tool for the job. The highly polished boring inserts for aluminum are truly lovely to use with kerosene as a coolant, but quite often plain old boring HSS well honed ends up being my cutter of choice while the really nice expensive polished insert tool is reserved for final passes where the time to swap tools is justified. Most of my machining these days is keeping stuff working and utilitarian though, hopefully time for nice little engines and such will be available soon.
Trying to do home shop work "like the big shops do things" is something I realized isn't practical in many cases. Industries needs are different than mine most of the time. I worked for a while in a large defense plant. We had lovely exotic machines, flood coolant that ran through huge pipes, every top of the line latest and greatest way to accurately and repeatably remove metal in high volumes at speed. When I needed to have a test fixture made one off I'd head down to see the guys in the model and prototype shop. Most of the machines were still old school but very, very, good manual and power feed rather than CNC back in the early 1980's. They were using jars of cutting oil and flux brushes or small squirt bottles for most stuff, just like me in my little home shop
Best approach? No idea, just what works for me with my equipment.
Cheers,
Stan
