Drilling stainless steel? (420 ss)

J

JMDesigns

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Sep 1, 2009
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I have a quick question about drilling 420 SS. I am trying to put a pocket clip on a handle/scale that is 420 SS. The hole is 3/32 (for 440 tap). I used a drop of 3n1 oil on it, and tried at my presses lowest speed, and with a new bit got nowhere. I looked at the instructions for the drill press (Delta) and it said 3000rpms for steel. Stupidly I went against everything I know and set it up to 3000rpms. Yup - I was drilling at first but then it quickly heated and melted the tip flat (Yay)!

So obviously I should go back down to 900rpms. I was also using a Milwaukee black oxide bit, so maybe I should use a Ti bit on the next try. Main question is this - I never felt the bit really bite in and start cutting. How much pressure should I be using? What should it SOUND like when I'm cutting (squealing)? Can I heat the spot I tried to drill with my torch and let it air cool to soften it (since I likely work-hardened the crap out of it)?

This is really frustrating, because I researched it and watched several vids on it before I tried, and I went and bought new bit as well as oil. The project I'm drilling on is an SS knifekits.com DDR balisong, and I would really prefer not to ruin it. I pretty worried at this point that I'm going to end up welding a bit into it or hogging the hole until it can't be tapped.

I've seen many pictures of these kits where people have done fully skeletonized handles, and yet I am beating my head against the wall over two 3/32" (4-40) tapped holes. Up until now I've had nothing but successes on my various knife related projects so this is really making me feel dumb. Any advice and encouragement that the more experienced could offer would be VERY helpful.
 
with that small of a drill you are going to want to run it fast. also lots of oil. when i drill ss i peck at the hole and add oil each time i come up out of the hole. that small of a drill is going to get hot very fast. so i would do it like this. try around 1500-1800 RPM. then put some oil where the hole is going. now start to drill with firm presure, you want a nice curly chip to grow out of the hole. now when you drill down about 1/16" pull the drill out of the hole. put more oil in the hole and repeat.
 
I usually get a piece of rod and dip it in oil and let it run down onto the bit while its going and like JT said go up and down alot to clean out the hole because it will gum up in the hole if you don't.
 
Well I gave it another go with a Ti bit and nibbled a bit more away, but it makes a terrible amount of noise (is that normal?) so I had to stop for the night. I'm not getting "curls" though, I'm getting smallish chips and like quarter curls at best. Am I not applying enough consistent pressure? I would describe what I'm doing as "pecking" at best, and trying to keep the bit clear of the hole unless I'm actually cutting.
 
more pressure when your drilling, if you aren't feeding hard enough you'll just rub the bit and burn it up, try a new drill bit, if you locate your hole with a #1 centerdrill it will be a lot easier.
 
They say that if you're not breaking a cutter every once in a while you're not pushing hard enough...

No, a horrible squeal is not normal. Reducing RPM and increasing feed pressure is normally the first thing you try. I would peck every .100" - which wouldn't be very many times. And I'd feed hard enough to get through that hole in about 10 seconds. If you're not feeding hard enough you're rubbing, which makes heat, dulls cutters and work hardens stainless.

There is a fine line between rubbing and breaking a .094 drill that I don't know how to tell you where that line is. But it sounds to me like you're on the underfeeding side of that line. Dulls them quick doesn't it.

If it is cutting well it won't sound like much of anything. Some say "sizzling bacon".

To reduce work hardening in austenitic stainless a trip to 750-1000F is recommended, I'm not sure about 420.
 
I'm guessing that machining and drilling are new to you. If you think that drilling this hole is frustrating, wait until you try and tap a 4-40 thread in stainless steel by hand.:eek:
If at all possible, take it to someone who does this often and have them show you how.
The learning curve on tapping is about half a dozen taps.
Stacy
 
I had this problem but it was on a hardened blade. What finally worked was a masonry bit for concrete, not sure what kind of tip it was. For unhardened 440C a regular metal/wood bit seemed to work ok.

I wonder though, if it is this hard to drill through, is a tap going to be able to carve into it? Ive never tapped anything before but have thought about it and want to know the answer.
 
JM: Since the first drill got red hot, your SS is work hardened. You will need a carbide drill from here, to have any chance at cutting the 4-40 threads. Also, a 3/32 drill is probably not big enough-I would suggest .101
The threads will be plenty strong to keep the clip on.

RJ Martin
 
Like the others have said, you need to peck the drill. You will know if it's cutting or not. if you are making chips, you are cutting, but not enough. you will start to see some curly chips when you are pressing hard enough. It is not unusual for stainless to squeal, but it happens more with the 300 serious non-ferrous stuff than it does with the 400 series steels.

Like RJ Martin said, you have most likely work hardened the steel. If you have you may need carbide to get through it. Whatever you do, don't run the speed up on anything unless it is carbide. start slow, say 400-500 rpm. I would use a center drill or something that may be a little harder than the drills you are using. Always start on the low sides of speeds and feeds, then work up if the cutter/drill can handle it. This is a good way to preserve tools. if the tool you are using is skating around on the hole or making a chipping sound then it probably isn't cutting, and you are just wiping the cutting edge off of the tool you are trying to cut with. It all has to do with hardness. what you are cutting must be softer than what you are trying to cut it with. if you have work hardened the hole, High speed steel probably won't even touch it - which is what most drills and center drills are made of.

A little hint: Take a bottle cap off of a coke bottle or some other drink bottle and fill it up about half way with oil. every time you pull the drill out of the hole, blow it off or clean it off, then stick the cap up under there and lift it up onto the drill. this way you aren't squirting oil all over the place and getting it everywhere. For what it's worth, coolant would work too, if not better. I use coolant on just about everything except for when I'm tapping - then I use tap oil. I mix sulfur oil and tap magic and two or three other things to make a potion
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When you are tapping these holes, you need to be sure that the tap is straight. When it gets down to the small stuff like this, I always hand tap them anyway. I may start the hole in a mill or drill press, but I always do the majority of the tap work by hand. Small taps are more often than not very brittle and easy to overpower and break. I would advise against trying to start the hole in a drill press if you have never done it. Once you get the hang of tapping holes, you can try it that way. The only real benefit to starting the hole in a mill or drill press is you know that it's straight.

When you get the tap started, turn it in about 3/4 or 1 revolution and then back it out about 1.5 or 2 turns. Then go back to where it starts to cut again and repeat. always back the tap up to clear the threads, especially on the smaller taps. Doesn't hurt to pull it out and clear the chips out every now and then either.

Hope this helps you out
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I'm going to be a little contrarian here, but folks please don't get your shorts in a twist if I disagree with you.

Considering that a standard size 4 screw can be a small as .106, and it is not uncommon for a drill to cut a few thou oversized, I don't recommend using a .101 drill because you stand a good chance of having inadequate thread engagement. Stick to the recommended drill for 60% engagement.

There is no good reason that drill should be carbide. Carbide is expensive and fragile. No, it won't "dull", but it could easily turn into a fluteless pick. The color the bit glowed has no direct bearing on work hardening. It is work hardening - it didn't austenitize - temperature is not relevant. It is not likely to have gotten so hard as to need carbide. Cobalt HSS is the correct material for a drill in a non CNC application in stainless. A sharp drill, pressed hard enough to pierce the skin will cut that hole. I'd even wager without oil or pecking - though they won't hurt.

The RPM that JT suggested works out to about 40 SFM for a .094 drill, which is a nice moderately slow value for HSS in stainless. Half that speed would be out of the recommended range but should still work okay, though I don't recommended going super slow because I don't believe the cutting mechanics work the same at very slow speeds. For example, a .094 drill turning only 300 RPM would be going under 10 SFM will tend to grab and possibly break.

I agree that tapping a 4-40 hole in work hardened stainless is no picnic, but it can be done. Use a sharp tap, a tapping fluid such as Moly-dee (EP grease works in a pinch), and keep it aligned straight and back it off as needed. I like to do the small taps under power because they cut better if you can spin it fast - but that requires special tools. And personally, I prefer to thread mill these days - but talk about special tools...

I hope I didn't piss any of ya'll off - not my intent.

JS, JT, good advice :thumbup:
 
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