[graemeian]

I am cutting a lot of fish mouths on 2.5" OD tubing. I am using 1" 5 flute HSS mills at 300 RPM and 4 ipm. The mill is long enough to cut both top and bottom of the fish mouth. The process takes about 3 minutes. The mills are old stock that I saved for jobs like this. I am cutting wet where my machine has 5 jets blasting coolant. No problem there. I have some P&O 1/2" plate where I need to mill 2.505" holes through the plate. I would drill a hole in the center and add a bolt leaving a thick washer. I would use a helical path with the carbide mill. My first thought was to use 3/8" AlTin coated carbide mills and air blast as every CNC machinists would tell me. I only have a loc-line for my air. The air would always leave chips which would be slammed by the end mill. Today, I have cut dozens of fish mouths with the HSS end mill and coolant. I do not think I would get this much tool life with air. Would I be better off using non coated carbide mills and the 5 jet coolant blast for my P&O plate?

[graemeian]

Hi,
I saw a similar thread and someone stated that water can cause thermal shock. However, most people use liquid coolant with aluminum and thermal shock is never an issue.