What type of bit do I use to drill holes in stainless steel? Nothing seems to work

Question

I recently bought some Damascus 1 inch ring stock (304 and 316 stainless). I sliced off about 8 mm of it using a bandsaw. I then stuck it in a vice and attempted to drill through it. I have tried silver/cobalt drill bits, masonry bits (didn't even scratch the surface), carbide tipped Forstner bits, and even regular wood drill bits.

Ironically the Lowe's drill bits worked the best. As I attempt to go up sizes moving from an eighth to a quarter to 5/8 to 1/2 in to 7/8 to 1 in I seem to dull the outer edge of the drill bit.

No matter what I use, after two or three holes the drill bit is toast and won't even grip the steel. I'm running my drill press on the lowest setting while using cutting fluid like it's water.

What am I supposed to be using? Should I invest in a solid carbide bit? After a lot of googling I think the only thing I haven't tried is a tile bit. Any suggestions?

Answer 1

Drilling stainless steel successfully is more about technique than the drill bit. Of course, using a completely wrong drill bit will not work (a forstner or wood bit on steel, much less stainless steel? - madness. A tile bit? More madness.)

Cobalt ( -alloyed hardened steel) or solid carbide bits should work.

Repeated attempts in the same spot with the wrong drill bit or wrong technique will make it harder - literally. Stainless steel work hardens. That means if you deform it, it gets harder. For drilling, that means you have to use enough pressure that you are taking a thick enough chip to remove the hardened layer, or your drill will stop cutting as the workpiece becomes harder than the drill is. If that stalls your drill, you'll need a more powerful motor or lower gearing.

Alternatively, grind it out with an abrasive, given the size of the part you are working with, and probably having work-hardened the surface already.

Answer 2

After a lot of googling I think the only thing I haven't tried is a tile bit. Any suggestions?

Plasma cutter? CNC waterknife? LOL

Seriously though, I had to cut 13 holes (some square to capture carriage bolts) in 50 sheets of metal. CNC plasma cutter ate it for breakfast, though I would've rather used a waterknife. Less rework.

masonry bits, and even regular wood drill bits
running my drill press on the lowest setting

There's your trouble right there. You're blind guessing.

For any given metal, there is one correct/ideal feed (the depth of cut) and speed (the linear rate of cutter movement through the material). If you're in the ballpark, fine. If you're not near, well, you found out.

Machinery's Handbook (or other resource) will have correct feeds & speeds for your material. In drills that translates into RPM (for a drill size) and plunge rate. Once you have the drill at the RPM the book actually says for that metal and bit, an attentive operator has a reasonable chance at finding the correct plunge rate/pressure, just by noting what force makes it cut "like butter" vs fail to cut.

But work fast. If you're "not cutting" for even a second, you are "work-hardening" the material. Too much of that and you're done. You'll need to find another spot, find another part, switch to waterknife, or do something thermally to remove the work hardening. But the latter may destroy the properties of the metal.

That's why you kept destroying better and better bits, you kept trying to re-drill the same place you'd already work-hardened.

Harper's rule of cutting metal: If you're not cutting, you're not cutting. STOP!!!

Once you get it dialed in, it's sheer pleasure. You're banging holes out very fast, using little oil, the bits aren't dulling and aren't even getting warm. (yes, all the drill press' power is being turned into heat, but the long chips like spaghetti noodles are carrying it away). That's your happy place.

Answer 3

You've discovered that the Lowes drill bits work best for this particular material. The only problem is that they're getting dull. If you don't know how to sharpen a drill bit, it's time you learned. All you need is a bench grinder, your two hands and your normal protective equipment.

It takes only seconds to touch up a slightly worn drill bit and get back to drilling. A completely messed up drill bit takes a minute or two. A normal jobber's length drill bit can be sharpened many, many times.

Start watching videos of "sharpen a drill bit freehand" and you'll figure it out.

Answer 4

Standard high speed steel bits are good. 316 and 304 stainless are not hard, they are tough and work harden rapidly . Cobalt is a common alloy in high speed steel, no particular advantage. High pressure , low speed plus cutting oil should be used. As several answers have noted , I will repeat; If bit turns and does not cut shavings, it has work hardened the stainless making cutting very difficult . Best to move to another spot. Also, drill a small diameter hole first , the drill the final size. the cutting oil makes a difference I have used old high sulfur oil. Worked well but now illegal per EPA.

Answer 5

Some excellent answers there, but I just want to give a bit more detail and explanation of bit diameters and pilot holes.

I feel your pain at starting small and going up in size gradually and being frustrated that it's dulling the outer edge of the bit. Been there, done that.

Then a friend whose dad had been a tool maker taught me how to sharpen HSS bits with a bench grinder, and pointed out the different aspects. Right at the tip of a large bit, you'll see that it does not go to a sharp point - it's more of a flat chisel. This doesn't cut, just scrapes the metal aside. If you need to use a large bit for the final hole, then start with a bit that is just a little bit wider than the flat chisel end of your large bit, to drill a pilot hole.

If your final bit is seriously large, then you might need a fairly large pilot hole, in which case you should choose a smaller bit to make a pilot hole for the pilot hole :) The smaller bit will have a much smaller flat chisel end, and so will be scraping less metal around, allowing you to cut more.

Describing the details of how to sharpen a standard HSS bit with a bench grinder is beyond my skills here, but it's well worth learning. When one of my bits stops cutting, I put it aside and sharpen it before using it again. That has made so much difference to my work.

In terms of speed and pressure, I've been doing most of my stuff by hand, so I don't know what speed and pressure I'm using - but my friend pointed out what others here have stated, that you should aim to be getting spirals of metal being cut off. I try to start with light pressure and build up pressure and speed until I see that happening. I'm not saying my style is perfect, but I've learned a lot over the last few years.

I hope some of this helps.

Answer 6

First find a way to clamp your workpiece securely without damage to the part or importantly you. is is 95% of any metal working job and is bound to take 90% of the time.

Read up on the ways to hurt yourself with a drill press ! https://www.youtube.com/watch?v=8Ri6poVpQM8&list=PLN8VIbn37NRnW-Kyo0FeaP0fkxLDLtBFc&index=1 this is something to watch out for regardless of material.

Any decent quality HSS-E or HSS-Co drill with the right geometry will work 135degree tip,lower helix angle so more and shallower "theads" (or just read label if suitable for stainless steel). don't cheap out. the $20 for set will not work on anything but the mildest of cheese steel and aluminium. Start of with firm pressure and increase until it cuts curls, about ~900 rpm for 1/8 ish, 500rpm for 1/4ish and will do for most sizes you will be able to cut , drop to 250 for 1/2 and up but that is unlikely to go great unless you have a proper drill press (meaning massive), cutting fluid.

Always use a center punch to start off!and let the clamp float to center. (a center punch is the shallow angle, a pointy one is a prick punch small tap with prick punch then a good whack with the center punch

try it out on some scrap, you probably need to dial in the pressure

Answer 7

I had luck with HSS drills. You need to go with very slow rotation and steady pressure. HSS bits can take a bit of wobble so no need for CNC. For 1 inch I will not be so confident to use a hand held drill.

Ideally you should cut large chunks, not dust. Sharpen it after couple of holes. The bit can bite extremely well at times, make sure you secure your work piece and your drill should be up to the task. If you are using handheld drill, hold it tight. Once I managed to wack myself with the steel profile with a corded 650W drill at probably 20-30 rpm. Be careful.

Answer 8

I just found this thread, while being stuck with the same problem. I was trying to make M5 holes in a bunch of M6 304 dowel pins I bought off amazon. I needed 304 to avoid corrosion with a 304 matching part. I was still in the process of setting up my shop after moving, so I had a go with a handheld drill (what the heck).

I had a bag of 10 brand new M5 cobalt drills from a dedicated shop, not amazon. It was a total nightmare. The frustrating part was that some pins would drill just right through (with nice chips flying out etc), while others would just stop as soon as the bit would hit the dowel. I tried smaller bits (M4 or M3), no luck. Everything was nicely clamped (except the handheld drill, of cource), no issues with walking etc. I wonder if these pins were a "mixed bag" -- some were hardened more than others (and I did not mean to buy hardened pins).

What I ended up doing, and this might sound crazy -- I used a 6mm OD Ti tube stock I had lying around and chopped it into dowel-length pieces. Ti is hard compared to well-behaved steel, but it was surely better behaved than these dang dowels. Corrosion should be not an issue. Got the job done.