.020" Hole in 304SS RPM?

[EmeraldIsleforg]

The company where I work is a Metal Injection Molding shop. We have a new part that requires quite a bit of secondary machining & we are looking into purchasing a new VMC in order to do it in house. My question is, according to the feed & speed calculators I need a spindle that spins at around 22,000RPM to drill a .020" hole in 304SS. Machines like this are quite a bit more expensive & harder to find. One vendor suggested that their 16K spindle machine should be able to drill it just fine. I wanted to find out if anyone has any experience drilling small holes in SS & could verify this? They are going to try it out for us probably next week, but I thought someone here might be able to give me a heads up as this will open up other machines as well.

Thanks for any tips!

Mike

[fizzissist]

(assuming HSS drills....) Buy good quality drills, designed for SS. 135deg split points, screw mach. length.

3500 rpm, .0005 feed/rev max. Peck 3/4 dia depth max. LOTS of flood coolant.

Start from there.

I found 3500rpm works well in 304L SS, you have to remember there's no place for the heat to go at that dia....so normal SFM numbers don't apply.

[Shane123]

or you can by a special tool that uses coolant or air to power the bit, and its geared for higher rpm like this.

[EmeraldIsleforg]

Thanks fizzissist! I'll give that a shot tomorrow in some test pieces.

As for the speeder heads, I'm a little concerned about runout & such in them. Also, there is a lot of other machining to be done on these & it would take a lot of time to swap them, I think. Might look into them more, but I'd feel better not using them I think.

[fizzissist]

Originally Posted by EmeraldIsleforg Thanks fizzissist! I'll give that a shot tomorrow in some test pieces. As for the speeder heads, I'm a little concerned about runout & such in them. Also, there is a lot of other machining to be done on these & it would take a lot of time to swap them, I think. Might look into them more, but I'd feel better not using them I think.

I've had to drill in 304L holes from .013" to .055" often blind. I found that the conventional SFM guidelines just gave me broken drills. Got some tech input from a vendor, slowed it down to 3500, and got much better results.

Maybe there's some guys who've done this with much higher rpm's, and I'd like to hear about it, but for my applications, this has worked.

I think a big help is simply a good, solid spindle with no run out or backlash, and good feeding ability, as with a good CNC mill. I don't think I'd run carbide, though in theory it should run circles around HSS, mostly because of
possible chatter on entering the spot drilled pilot hole, or re-cutting a chip left in the hole from the last pass. HSS is more forgiving like that.

One application was .055" dia holes x .130 dp in 304, +/-.001", and I never broke a drill. Patience is the key.
Good luck!

...btw....test holes in test parts saves fixing test holes in real parts.

[EmeraldIsleforg]

Originally Posted by fizzissist I've had to drill in 304L holes from .013" to .055" often blind. I found that the conventional SFM guidelines just gave me broken drills. Got some tech input from a vendor, slowed it down to 3500, and got much better results. Maybe there's some guys who've done this with much higher rpm's, and I'd like to hear about it, but for my applications, this has worked. I think a big help is simply a good, solid spindle with no run out or backlash, and good feeding ability, as with a good CNC mill. I don't think I'd run carbide, though in theory it should run circles around HSS, mostly because of possible chatter on entering the spot drilled pilot hole, or re-cutting a chip left in the hole from the last pass. HSS is more forgiving like that. One application was .055" dia holes x .130 dp in 304, +/-.001", and I never broke a drill. Patience is the key. Good luck! ...btw....test holes in test parts saves fixing test holes in real parts.

I just tried it & it works GREAT so far!! Thanks for the tip, I really appreciate it! Got 4 .095 or so deep holes drilled with the same drill right now & seems to be going strong still.

Mike