I am drilling in Anodized Aluminum 0.156" holes using a porter cable (27500 R.P.M) with a feed rate of 7.5 on a CNC Router. The drill bit is 2 step ( 0.156" / 0.200" with 100 deg chamfer) made from 0.500" carbide wih TiN coating on it. The problems that I am facing are:

1. Aluminum chips Built-up into the flute of the drill bit
2. burs at the bottom of the holes.
3. R.P.M. is too high, this way the manufacturer set the feed and speed.
4.If I try to reduce the RPM the bit breaks from the 0.200" dia.

Can anyone help me in setting up these parameters to get an efficient and clean job done.


Thanks,

Kaleem

Use coolant on the drill. The flutes are likely plugging from excessive heat generation, because the feedrate should be more like 50 to 60 inches per minute at those kind of rpms. If you can, slow your spindle down, and feed the drill at .002 to .004" per revolution. This heavier chip should force the chip to travel up the flutes.

To ensure that some coolant gets down the hole, you might also peck drill in steps of .05 to .1" at a time. This will also help chipbreak to occur.

Step drills are bad for that. NO where for the chips to go, especially around where the drill changes the diamater. You may want to try more flutes, or even pre-drilling.