Drilling stainless

[loose nut]

I had to drill some SS tubing before threading, I used the proper sized drill which was just ordinary HSS. Didn't drill worth $#!+. Sharpen ,drill, sharpen, drill etc. Finally I dug out the 135 Deg Cobalt drills, didn't have the right size so I drilled it with the next size down, zipped right through it. Now I had to go back and drill it to size with the HSS drill, still didn't drill very well and I was just clearing out a bit around the outside of the hole.

Why so much difference.

[boslab]

If the drill is even slightly dull, and you back off the pressure the damn stuff will work harden to the point that the drill will glow red without so much as scratching, you have to get stuck in and keep the pressure on, can be tough to deal with.
I've found bullet points work good on a hand drill, I got some dewalt ones that work good
Mark

[Magicniner]

If you run the HSS with too much speed and not enough pressure your stainless will eat the edge, use a low gear, good lube and keep it cutting, let it rub and you're done for,

- Nick

[BCRider]

I've got a hunk of SS round bar that does just what these guys are saying to HSS tool bits. I eventually got the part done that I wanted but it was an education.

There is a lot of different stainless types so the next one you work with might not be a problem at all

[johnnyd]

If it ain't 303 or 416 yer gonna be doin' a lot of cussin'.

John

[plunger]

Is it true that a sharper bit works better By that I mean instead of the normal 118 degrees a 130 or so degree is better. An hss with cobalt is what worked for me with much slower speed than you would think.?
I hate stainless.

[LKeithR]

Most home shop drill presses and virtually all hand held drills are just too fast for drilling SS. When drilling SS you've got to turn the drill "really" slow and maintain a steady feed rate. Most of the low dollar--think Harbor Freight or Princess Auto--drill bits are junk as well. If you get the speeds and feeds right, use a "quality" drill bit and a good cutting fluid then drilling SS--even 304--is not that big a deal...

[Ries]

I have drilled literally tens of thousands of holes in 304 stainless. All, using perfectly ordinary HSS drill bits.
I had one project where we set 6000 1/4" rivets, which meant drilling between 12,000 and 18,000 1/4" holes in 5/16" stainless plate.
We went thru about a dozen HSS drill bits on that project.
The trick is, as mentioned above, a slow drill- we used a bridgeport running at about 150rpm for those. And, lube. I use CoolToolII, as I can get it in tiny squeeze bottles, easy to apply it to most any hole.
My go to hand drill for stainless is a Bosch 1034VSR- thats a variable speed drill that tops out at 550rpm, and is easy to keep at 100rpm or so.
Then, lots of pressure. You got to really lean into it.
If the ss gets hot, you stop, sharpen the drill bit, and then, lean hard, go slow.
I have never had a problem cutting thru the hardened 304, if you run the bit slow and apply enough force.

[Mike Burch]

I learned the hard way when boat-building that to drill 316 you need:

slow speed;
constant pressure, and lots of it;
a very sharp drill, and;
cutting oil.

Omit any one of those and the damned stuff work-hardens like you wouldn't believe.

Keith is right—cheap drill presses and hand-held drills are just too fast-revving. I replaced the 4-pole motor on my Ryobi drill press with a 6-pole for that very reason.

[TN Pat]

Ya, all of the above. 135-degree point is best for tougher material. Perhaps 30 surface feet per minute when using cutting oil. If you have flood coolant, 70. This is assuming good, quality HSS drills, such as Precision Twist Drill. So... for example, perhaps around 500 to 600 RPM with a good 1/4" drill. Whereas 1018 might be 1000, for example.

[Mike Burch]

I should have added to my list above "Go easy on the centre-punching".
Centre-punching hardens the punched area, which makes it difficult to get a pilot drill started.

[wizard69]

I had to drill some SS tubing before threading, I used the proper sized drill which was just ordinary HSS. Didn't drill worth $#!+. Sharpen ,drill, sharpen, drill etc. Finally I dug out the 135 Deg Cobalt drills, didn't have the right size so I drilled it with the next size down, zipped right through it. Now I had to go back and drill it to size with the HSS drill, still didn't drill very well and I was just clearing out a bit around the outside of the hole.

Why so much difference.

Stainless is tough to work with. HSS will cut stainless but you need good quality HSS that really is sharp? In my experience few up can hand sharpen drills and have them work well in stainless.

As somebody has already mentioned stainless can work harden to an incredible extent. You can literally burn up a drill bit and basically end up screwed as far as getting through the piece.

As a general guide:

1. Use sharp tools on stainless.
2. Keep you spindle speeds down. It doesn't hurt to cut the speed in half relative to what you might use of plain steel.
3. Keep a somewhat aggressive feed rate. The thing with Stainless is that it is hardening as you drill it, you want the drill to feed fast enough so that your cutting edge is underneath the hardened edge.
4. Never. Absolutely never, allow the tool to rub or idle where you expect to cut. Again it is the problem of work hardening which can be significant with some alloys.


Probably the most important thing, atleast in my experience, is to keep the spindle speed down. My occupation is in plant maintenance where we work extensively with stainless steels, it is very easy to screw up and choose the wrong spindle speed and end up with an ugly mess. This especially when production is waiting on something.

When hand drilling and possibly machine drilling the other big mistake is choosing a drill bit that is too big. If you can't sustain the feed rate with a hand drill you can work harden the piece and suffer as a result. It is always a good idea to step drill with a small pilot drill first and then migrate to the bit you want to bore the proper hole. Sometimes you need to use three bits. Also in hand drilling you need suitable power in the drill as you don't want the drill to punk out in the middle of the hole.

[smithdoor]

FYI If the ss is magnetic this type will work harden very fast keep drill bit very sharp and lot of dark cutting oil


Dave

[loose nut]

Thanks for the reply's.

I was using a Cordless drill, only way I cold get to the place on the assembly to drill it. Drilled slow with oil and lots of pressure, at least the most that I could get and it still must of hardened. I will say that right from the beginning it didn't want to cut the SS (304 or 316). Anyway jobs done.

[wdtom]

What others have said about slow speed, sharp tools, a lot of feed pressure and good cutting oil is true. The reasoning is you need to get the next cutting edge that comes around under the work hardened surface from the previous cut. Stainless work hardens easy and when it does and the tool is a little dull that is the end of the road, at the first sign of dullness you might as well stop and sharpen right now. Pushing it just makes it harder to get started with the sharp tool after you finally give up.