When you're machining with high feeds and speeds (how fast you move the cutter through the material, and how fast you spin it) there's a lot of heat that can build up on both sides. If the chips you're cutting off the workpiece get too hot or stay near the cutter too long, they can weld themselves to the cutting edge and blunt it, leading to tool failure. That's why it's so important to use coolant for machining operations. Not only does the oil in the coolant help to lubricate the cut and make it easier to move through the workpiece, but the flow of liquid over the cutter and the chips helps to move the hot metal shavings out of the way and draw heat from the cutter so it can keep working.
Up until a few days ago, we were limited to mist coolant in our Tormach at work due to a combination of budget & mess issues. Over the weekend, however, one of the other mill-heads in the shop slapped together a home sump pump and some garden hose to build a flood coolant system:
Now we can cut at much higher rates! The one downside is that when you turn this thing on the interior turns into a wet hellhole and the enclosure leaks like a sieve. I've ordered some new parts to help professionalize the build a little and seal the enclosure, but as things stand now there's a definite improvement in cut quality and reduction in chatter!