drilling 304 stainless

B

Brad Lilly

Moderator and Awards Boss
I'm trying to drill some 304 stainless and getting no where. I tried to anneal it in my forge, brought it up to 1600deg shut the forge down and left it for 5 or 6 hours and it is still hard. What am I missing?
 
I have to agree with Cal. I wish I had better info, But aside from Carbide its gona fight you all the way!
 
I was trying to drill the stuff to make a template. Now i think I'm going throw it in the scrap bin. I don't know where to get 304 pin stock.
 
For 304 ss grind your high speed or cobalt drill bit at a bit flatter angle , cut the speed of the drill down and use a good moly based cutting oil like "moly dee" . The moly dee makes it drill like night and day comparing to other cutting oils. Oh , and use a centre drill to prevent the drill from wandering unless you are using a stub length drill bit.
 
i would do as Paul suggested and use a cobalt bit with good cutting oil. I use the "screw machine length" or "maintenance length" bits from McMaster-Carr, very reasonable prices. I have to drill some 304 and a lot of 316L at the office. 304 & 316 will polish and shine better than any other stainless. as far as pin stock, again McMaster-Carr, 304 stainless, 1/8" diameter, 72" length for less than $9.(303 and 416 are even less) thats a lot of pins.
the old sailor
 
I use cobalt drills. I use 3/32" size with slow rpm's and steady pressure so it doesn't slide on the top of the cut and work harden. If it does that forget about drilling that one and start over. I get all my 304 pinstock from Sheffield Knife Supply. I use 3/32" because it is easier to peen out and make the pins invisible. I use 304 s.s. all the time.
 
I agree with paul savage. Speed and feed are key. And PLEASE don't waste a carbide bit. 304 grabs really bad and will even break cobalt bits if you aren't careful. It would be nearly impossible to drill 304 with carbide and not break the bit, which is not only frustrating because carbide bits are freakin expensive, but also because you're often left with a hole filled with carbide pieces that are too hard to drill out. Stick with 416 and you won't regret it.
 
Y'all make it sound like 304 is some really bad stuff to work with. And maybe the stuff you have is, I've heard some folks who got imported material that gave them a lot of grief. But normally 304 really isn't that bad. And it has much better corrosion resistance than 400 series material.

There is no place for carbide in this application. Quality USA made HSS or cobalt HSS is the key. This is a good application for a 135 split point, though I've used 118 for this without problem. I use Chicago Latrobe for my general purpose drills. They're not expensive and they hold up very well.

The biggest problem most of you guys have is underfeeding it and then trying to cut with a dull cutter. Don't underfeed and don't try to cut stainless with a dull tool you'll only work harden it.

The key to success is a quality tool ($2.00 USA HSS drill bit) and to feed it right. It has a narrow window compared to other materials. You can push a 3/32 drill through aluminum at 2 inches per minute up to 40 inches per minute, no problem. Wide window. Stainless has a narrow window. If you will turn your 3/32 drill at 1200 RPM and feed it at 2 inches per minute you will have no problems. If you underfeed it, it will rub instead of cut which will quickly dull the drill and harden the work piece. That bears repeating: If you underfeed it, it will rub instead of cut which will quickly dull the drill and harden the work piece.

Use a cutting fluid if it makes you happy but it really doesn't do a whole lot drilling shallow holes.

The chips will come out in a curly cue as a bare minimum to indicate you're feeding it hard enough. I generally feed it hard enough the chip breaks and I get short thick fat little chips. If you're squeaking and getting a birds nest around your drill you're not feeding hard enough.

Once the drill is dull, stop. 3/32, throw it away. Fed properly you can get hundreds of holes. Fed improperly it can dull in just a couple.

Other than underfeeding, the next big thing people run into is overfeeding. This generally happens once the web of the drill exits the back of the work piece and you lose the majority of the resistance to feeding and you overdo it. So be careful once the drill starts to exit the back side of the work piece, otherwise it is easy to wipe out the corners of your drill.
 
I have never noticed 304 being hard to drill. A bit gummy, but not hard. You can get a variety of stainless tig rod at any welding store. 308 rod is very close to 304
 
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