Drilling 304SS

[TT350]

I need to drill 400 holes threw .250 thick 304SS,
hole size is 7/16.

I normally use HSS uncoated 118 deg screw machine
drill bits in a manual mill.

I plan on doing this job in my CNC mill,
can you guys recommend a better drill bit and
feeds/speeds for best tool life and a clean hole?

Thanks
Chris

[laka]

I've used Sandvik, Kennametal, and Mitsubishi carbide coolant thru drills in 304/316 with very good results. If you have thru-spindle coolant look for a drill that will accomodate it.

[TT350]

My mill has flood only.
What about feed/speeds?

[gsrmmeza]

for the hss drill that you have i would use the following
(4 x sfm)/d=rpm

sfm=50

d=.4375

(4 x 50)/.4375= 457 rpm

rpm x cpt x # of flutes = feed

rpm = 457

cpt = chip load per tooth = .002

# of flutes = 2 flute drill

457 x .002 x 2 = feed rate of 1.83

so rpm=457 feed=1.83

this is what i would use myself

[TT350]

Thanks I'll give it a shot!

[HuFlungDung]

I've tried and like a high helix cobalt drill for flood conditions. Dormer makes a nice set of high helix drills. Because 304 is soft, the high helix with split point promotes chip flow somewhat better than regular jobber drills. Moderate rpm allows coolant to get to the drill, and still you can keep the feedrate in the aggressive zone, so long as the drill is sharp and cool. Stop immediately if you hear an anguished squeak, and resharpen.

[laka]

With a decent solid carbide drill, you'd be able to get the SFM into the 200 and above range. And chipload would probably double.