drilling SST?

Drill press? Way too slow, 1,200 rpm min. drill a few seconds ease-up let the coolant flow down dill a few seconds and so on. Sharp, good bits a must! Learn to sharpen them by hand, the girls think it's cool.

You can't have too much coolant. 300 RPM is quite slow for such a small drill so you're OK on speed. You probably are not feeding aggressively enough to avoid rubbing a hard spot in the hole. Lean on the quill a bit harder, keep that chip going. You want your curly chip to be more than a shaving.

Stainless steel (in general, and some grades in particular, 310 among them judging by other replies) has the nasty behavior of work hardening as you cut it. Thus, you cannot take light cuts and get away with it. Odds are, you are not applying _nearly_ enough feed pressure. If the chips are not heavy and substantial (making you want a pair of gloves on to remove them, lest they slice your hand open) you're not cutting hard enough. Likewise, when you cut it on a lathe, you have to take a fairly heavy cut, or you'll take no cut at all.

Harder drills can help some, if you happen to be using a "regular drill bit", but technique is key with stainless - maintain pressure, or back the drill right out, and when restarting, maintain pressure - do not "ease" into (or out of) the cut or at any time cut lightly, or the cutting face hardens up, dulls the bit, and hardens some more.

--What they all said and don't forget to chamfer the lip of the hole before you start tapping it. Use a good tap lube too; I'd suggest "Moly Dee". Also you shouldn't need to tap the hole the entire 1/2" depth to get good thread engagement.

Jim

Afterthought: since you're in learning mode (we all are!), consider getting a couple of #36 or #35 drills and scraps of 310, and see just how hard you can lean on them before a drill snaps. This'll give you a feel for how much axial force you can prudently use, with no cursing or frustration involved. Might be among the best 2 bux you ever spent.

Only in Cleveland (:

Works for me!

Shame on you, Tom. That speed in stainless is a sure recipe for failure.

Keep the tool sharp, don't let it idle---and don't run too fast. Stainless work hardens quickly----and what you described is exactly that---work hardened. If you look carefully at your drill, you'll find it's well worn at the margins, and is now drilling a tapered hole, or trying to. The drill, in order to be restored to being useful, will have to be pushed back until the margin is not altered. Could be as much as 1/8", depending on how long you leaned on the drill. You heard the sound of a drill grabbing and then slipping fairly rapidly. That's the nature of stainless.

If you have choices, do as Gunner said, use 303. Se is the best to use, but S is very acceptable. Each is slightly lower in corrosion resistance, but the difference in machining is huge. If you can use a 400 series, 416 is even better. It's heat treatable, and is the best machining of all the stainless family.

Harold

That's a mighty small bit Harold, but in retrospect, I wasn't thinking. That stuff does work harden easily. And most of my experience is with 302.

...but you had to like my "hand sharpening drills gets the girls" thing. Susan considers that your finest attribute.

If I did the math right, your 300 RPM translates into about 10 surface feet per minute.

If you use a 50 SFM as a starting point, the RPM should be around 1500 RPM.

At 300 RPM, you are rubbing the drill bit to death. (eventually) Especially when going 3/4 deep. Increased RPM should show a vast improvement.

Good luck!

Hard to argue with that!

Hey-------wait a damned minute.

How do you know what Susan likes?

I'm gonna have to keep an eye on you two.

C'mon, man, we _all_ know what Susan likes.

(Oh good, he only knows about two...)

I feel somewhat vindicated! (Where do I send your check?)

Correct! You want a good example? Buck a stainless rivet, even one made from 303 S, for a prolonged period of time, then check the hardness of the head with a file. Make the file an old, useless one, for the teeth will be instantly dulled where they contact the rivet head. Heat plays no role in work hardening----although heat may be generated in the process, and probably is.

I would only add that I

Yep, that's right, too. The chisel point of a drill is extreme negative rake, so it doesn't cut, it displaces. Cold working stainless is a quick recipe for work hardening, and that's what you're doing when you drill with a conventionally sharpened drill. A thinned web, or a split point is often the solution to the problem of work hardening, but the toughness of stainless is correspondingly hard on split points, so one must achieve a delicate balance of cutting edge design to achieve longevity of cutting tools and cut without hardening. Needless to say, a one-off project wouldn't be as critical as a production run.

Harold

I have a favorite saying, good tool steel isn't cheap.

The way out of the problem is to use a high cobalt drill, from a reputable manufacturer. Then do all the details right:

4) choose the correct sfpm for the drill so the edge does not break down from being run too fast.

Aside from work-hardening, stainless steels exhibit a very low thermal conductivity. This is the reason that sfpm numbers like one would use for carbon steels will put a drill out of action in stainless, rapidly. Noplace for the heat to go.

Jim

Not only that but SS sticks to the cutting tool. As it comes off it will pull particles out of the cutting tool which makes it dull fast. The less time you can keep the drill in contact with the work the better. ERS

Thus transferring the primary problem to the pilot hole drill, instead. :-) (Granted, it is easier to maintain sufficient pressure on a smaller drill bit, unless you have proper power feed.)

And a split point should eliminate the need fro the pilot hole, as there is no dead center.

However, larger split point bits of good steel are more expensive, so get several of the smaller split point high cobalt drill bits (the same diameter as the web of the larger drill bit) and you can use somewhat less expensive (and easier to sharpen) larger bits. It is a lot easier to sharpen to a chisel point than to a split point, unless you have special equipment for the purpose.

The rest (which I've snipped from below) was good advice anyway.

Good Luck, DoN.