Drilling and tapping 304L plate. 4

[spooky]

I need to drill and tap approximately 30 holes in a two inch thick baseplate made of 304L stainless. Is there a need for special drills and taps?

 

[Rich2001]

Generally, no you do not special drills and traps, through you do need to reduce you speed, use copious quanity of lubricate and coolant. Austenitic stainless steels galls and has poor thermal properties.

drills 118 deg point angle, 10-12 deg lip relief, 120-130 deg chisel angle, 24-32 deg helix

Extensive data can be found in The machinist Handbook as to recommendations. Sorry I don't have on on my desk right now, someone walk off with my copy .

 

[TVP]

I have some good info on drilling and tapping stainless steel that I will post tomorrow. In the meantime, can you tell me what the diameter of the holes are supposed to be?

 

[spooky]

The holes are for 3/4-10UNC bolts and 1.0 inch holes for dowels (light press fit).

 

[TVP]

Typical speed for drilling would be 15-18 m/min (50-60 sfm) and feed somewhere between 0.175 mm/rev (0.007 inch/rev) and 0.30 mm/rev (0.012 inch/rev).

Tapping speed should be around 5.5 m/min (18 sfm). Tap should be a typical tool steel like M1, M7, or M10.

As Rich2001 mentioned, use a lot of lubricant during drilling and tapping.

 

[spooky]

Just a follow-up. We used the slower speeds and lots of thread cutting oil lubricant and things worked fine. We used water as a coolant and lubricant on some of the holes where we could not disassemble the parts to cleanout the excess lubricant. It worked well as a coolant and less well as a lubricant. we had to sharpen the bits twice as often using water.. Thanks for the tips. Spooky

 

use plain hss drill bits and mystic metal mover as a cutting fluid, don't use oil as it is worthless in this application. when the bit dulls, STOP DRILLING IMMEDIATELY or you will work harden the SOB so bad it will take you as long to finish one hole as it does the other 29. I cannot over-emphasize this, keep the bit sharp, and use a little slower feed than what TVP suggested, you'll reap the gain in tool life. (304 can heat up terribly under a high chip-load, the heat does not go out with the chip as in plain carbon steels.)