Originally Posted by Rich05  Right now they are shiny on one side bluish grey other. Only running at 550 rpm with slow feed and .1-.05 depth cut, usinng carbide 1/2 endmill, mild steel....
Thanks R. |
Nothing wrong with blue chips, see the picture.
But you cannot do this with a half inch end mill; I was using a small face mill.
However your speed is much too low: Machining mild steel with carbide you can run at 400 feet per minute (that is the peripheral speed on the cutter; dia x pi divide by 12); this is about 3000 rpm for a half inch cutter. Some people might even suggest going higher but I am a bit conservative, I might even go down to 2500 rpm.
Using flood coolant when machining steel can be good or bad; if it is truly
flood so the cutter is always thoroughly drenched in coolant that can be okay, but if the cutter is only covered intermittently with coolant it is not good because the cutting edge gets hot and then chilled with coolant and carbide does not like this. It can lead to thermal fracturing of the edge and early tool failure.
You need to try some experiments running dry, or preferably with an air blast on the tool. Start at something like 2000 rpm with a feed of 0.002" per tooth; this would be 16 ipm for a four flute cutter. Keep your depth at 0.1 or even more; sometimes when you go with a very small doc, especially with a slow feed, the very tip of the cutter overheats because the chip is too small to carry away the heat.