Drilling in 303

[krwith121]

Hello all i am currently working on a job that requires me to drill through a 0.5" block of 303 using a 0.368" drill for a 7/16-14 tapped hole. MSC recommended a cobalt screw machine length drill bit with a 135° drill tip and no spot/center drill as it is a rigid setup. They recommended 700rpm, 5.0-7.0feed, and no peck cycle. The drill had constant coolant but still burnt up around 0.4" deep leaving the drill unusable, and the part with scorch marks. Can someone please recommend a better speed/feed, peck/no peck, and spot/no spot while still using the same cobalt drills i have on hand?

Edit* the material is actually 304 and my question still stands.

 

[FredC]

I do not have my feeds and speeds calculator handy but I gotta ask, are you sure of the material? Not 347 or 321 by mistake? Did the chips that came up look right for 303?

 

[krwith121]

I do not have my feeds and speeds calculator handy but I gotta ask, are you sure of the material? Not 347 or 321 by mistake? Did the chips that came up look right for 303?

I am now being told that it is 304 SS even though my paperwork calls out 303 because the part could be made with either. *sigh* gotta love lack of communication with the higher ups.

 

[plastikdreams]

Good luck drilling the burnt part...gonna need carbide or scrap it. 700 rpm at 5 ipm is way too much. Maybe 1200 rpm at 3 or 4 ipm with a peck every .1 or .2, full retract to get the coolant in there.

 

[crossthread82]

Since when did MSC start giving out speed & feed info that will work? If they give you something that'll burn it up they get to sell you another one...

 

[EMTech]

S620 F2.8 Is about where I would start on a .368 cobalt drill in 304ss.

 

[ARB]

I avoid drilling 304 without TSC if I can. I love the 1000 PSI TSC for drilling and tapping 304

 

[alek95]

TSC would help massively for this.

With a cobalt drill, I would probably do around 600 rpm and 3 ipm, with a full retract every .063

Carbide would be the best of course. Would make easy work of this.

 

[DanASM]

I would be at .004" IPR on a vanadium HSS drill / Cobalt drill. TiN coated if available. 45 SFM would be safe. I would probably drill it all in 1 pass with no pecking. Entry and Exit will have harder material and can give varying cutting parameters.

Tapping might be a little harder on the tap. Use lots of cutting oil or tapping fluids.

These #'s are safe #'s. If minimal holes are to be drilled. No dwelling anywhere, I use spot drills and 120* Vanadium HSSE drills specific to S.S. . Cobalt of any name brand should be fine.

 

[guythatbrews]

DanASM's recommendations are good. 45 SFM is 467 rpm. 700 RPM and .007 chip load is, well you know what it is now.

I would never ask a vendor for cutting parameters. If you wanna ask someone, call the drill manufacturers tech support line. That is what they do.

 

[krwith121]

I would be at .004" IPR on a vanadium HSS drill / Cobalt drill. TiN coated if available. 45 SFM would be safe. I would probably drill it all in 1 pass with no pecking. Entry and Exit will have harder material and can give varying cutting parameters.

Tapping might be a little harder on the tap. Use lots of cutting oil or tapping fluids.

These #'s are safe #'s. If minimal holes are to be drilled. No dwelling anywhere, I use spot drills and 120* Vanadium HSSE drills specific to S.S. . Cobalt of any name brand should be fine.

Thank you for the information. With your recommendations the drill went right through no problem leaving behind a nice beautiful hole and about a 5.0" long spiral chip.

 

[DanASM]

Thank you for the information. With your recommendations the drill went right through no problem leaving behind a nice beautiful hole and about a 5.0" long spiral chip.

Good. I am Proud of You.

 

[specfab]

I am now being told that it is 304 SS even though my paperwork calls out 303 because the part could be made with either. *sigh* gotta love lack of communication with the higher ups.

No wonder. The machinability of 304 vs. 303 is like night and day, in my personal experience. Glad you ended up with a way to git'r'done.