Drilling Stainless - Where did I go wrong

[magic_garage]

Hi all,

I had to drill 4 holes into 304 or 316 stainless steel plate for #10 screws. I'm not exactly sure on the thickness but I'd say 1/8" or a hair bigger. I'm not in any trade so my skills are limited.

I did research on drilling into SS and thought I was ready for the challenge. I bought 2 cobalt bit sets. 1) Cheap, good review set (M35), and 2) Bosch C014B set (M42) both from amazon. I also bought cutting paste. I used an early model Milwaukee M18 Fuel drill with the keyless chuck, drill/driver mode only, realy clunky compared to today's drills.

I had the plate on a cart so I had a good working height to work from and could put good downward pressure.

First mistake was I forgot to bring something to punch/dimple the plate so I used a dewalt gold 1/16" bit to make my dimple/starter hole. That went easeir than I expected so that gave me high hopes for this. I originally wanted to use self-drilling screws so I got 410 SS Torx head to use. I then tried to use the screw but the screw kept bobbling so I couldn't put enough downward pressure for the screw to drill. My target hole size was 9/64" so for testing/learning purposes, I grabbed another dewalt gold bit 7/64" or 1/8" (i forget) to try and step up the hole but that went nowhere. I made sure the paste was on there and I had my drill at #1 and no more than half trigger. I kept stopping to make sure things didn't get too hot. After that, I grabbed the 1/8" cheaper set cobalt bit and that went pretty easy. I then grabbed the 9/64" cheaper set bit and this is where it failed. Again, I made sure to have paste on, and speed at half trigger and lots of stopping, but I ended up going only mabe 2/3 of the way after a whole lots of stopping and trying. I was being very persistent with trying to drill the hole with this bit. I finally grab the bosch bit and it went thru like a breeze.

So where did I go wrong? Was the bit from the cheaper set that junk? I'm a little skeptical on that part. And what about the self-drilling screw? I read so many people saying it's fine to use those screws but I couldn't get it steady. Was it because of the torx head? Would phillips been better? I couldn't get what I wanted in hex head. Do I need to step the hole for such a small target hole size? The downward pressure part is little hard to determine based on what people are suggesting but I was afraid of putting "a lot" of pressure because of the smaller size bits I'm working with.

Please help.


Thanks!

 

[Beerhippie]

Drilling stainless--especially food-grade 3XX--takes a very slow bit and LOTS of pressure. Anything else work-hardens it instantly. I generally use thinned Anchor Lube for a cutting fluid, but kerosene and WD40 also work well.

A step bit works better on SS sheet metal than a twist drill, and carbide should not be needed.

What kind of backing did you have? Dampened wood is best as it will dissipate some of the heat of drilling. The worst I've encountered was drywall while installing SS backsplashes in a kitchen. That made it almost impossible to drill and I eventually had to shoot the holes with a plasma cutter.

Once the SS is work-hardened, not much of anything will cut through it short of a plasma. Best practice is a very slow--like 150-300 rpm--drill press, and lean on it.

 

[RTM]

I’m gonna guess the answer is the steps were too small, especially in the second case; 1/8” to 9/64” is trivial, and I think you need to be taking a bigger bite for the drill to work well.

 

[Notgrownup]

Slow, lube and pressure.

 

[Dave455]

Hi,

Couple of things.

First off, stainless can be quite a tricky material to drill, so you need good quality bits. Undoubtedly, the cheaper set you had were not up to the job. They may say “Cobalt” on them, but not all cobalt is equal!

I would probably have my doubts about the Bosch too. Although they make good power tools, the majority of their drill bits are made in China, and they are not in the same league as a drill bit from a metalworking supplier.

Secondly, the type of drill bits. If you get one from a specialist it will be a “quick helix” drill for stainless. You may not think it makes a difference, but the helix pitch alters the angle of the cutting edge, and that’s critical.

Thirdly, the downforce. However firmly you hold it, a hand held drill is not the right tool. Even the wrong drill bit, used in a drill press that’s totally rigid, and has decent downforce, will work.

I realise it’s not always possible to put the work in a drill press, but sometimes it’s nearly impossible without. If you don’t have a drill press, can you take the work to someone who has?

Everything else sounds good though.

 

[KnurledNut]

So where did I go wrong?

From my experience, for such a small hole it would have been better to center punch the location and drill it once with the desired size instead of drilling a starter hole and then stepping up.

 

[nafets47]

You should center punch it, use the correct size drill bit, drill slow with a lot of pressure, and use cutting oil.

By reading what you did it looks like you just made the spot you were drilling more difficult for yourself by using another bit which probably made the metal even harder in that spot (done that myself a few times). At which point it is a pain in the *** and a bit of time to correct the mistake.

When drilling you should see a consistent fluted spiral coming out of your drill bit while you drill.

 

[cannuck]

Many people confuse drills with reamers by trying to "step up" a bit at a time. For small holes: one shot only and for large holes a pilot just bigger than the web formed by the root of the flutes. As others have pointed out, low speed and high feed pressure. The secret with ANY cutting operation is to keep the cutting edge cutting as when it skids over the material without cutting it very rapdily gets super hot - annealing the drill bit and potentially hardening the material you are trying to cut. And of all the materials where this matters Ni and/or Mn alloys are the worst.

 

[ALinCarolina]

Agree with slow speed and much pressure. Maybe it wasn't necessary but for lubrication I literally flood the spot almost continually to keep the temperature low.

 

[CGarage]

1) Center punch it
2) Low speed, high feed
3) Need coolant for the drill bit, if only a few holes WD40 or tap magic, if more than a few, synthetic spray oil from Royal Purple or Amsoil…..there are more exotic coolants / lubricants used for this in aerospace, but I take it you are a hobbyist
4) Use professional drill bits, but Bosch makes some of the better “off the shelf” general drill bits and should be fine for a few holes.
5) Both stainless steel and titanium are worked similarly and not a lot of fun

 

[Rinspeed]

I've drilled thousands of holes in SS and you really need good bits. As mentioned slow, slow and slow because heat is your enemy. A Starrett snap punch is a wonderful thing if you have many holes to punch and almost a necessity for really hitting your mark.

 

[Steve_P]

Slow is nonsense. If you try to drill a 1/4" hole in 304 SST at 80 RPM you will get nowhere. But try.

You need good bits. Stainless is not hard but work hardens during drilling.

 

[Rinspeed]

Slow is nonsense. If you try to drill a 1/4" hole in 304 SST at 80 RPM you will get nowhere. But try.

You need good bits. Stainless is not hard but work hardens during drilling.

Lol.

 

[magic_garage]

Slow is nonsense. If you try to drill a 1/4" hole in 304 SST at 80 RPM you will get nowhere. But try.

You need good bits. Stainless is not hard but work hardens during drilling.

I think this is the first I'm hearing slow is not necessary, outside of this thread. To give me a better idea, assuming a typical 18V cordless drill, you're saying #2 at full trigger is ok in terms of drilling speed?

Actually, this is what I see people typically do and they have grave difficulty.

Thanks for your response.

 

[magic_garage]

Thanks for everyone who chimed in. I'm still not clear on a few things.

Regarding the self-drilling screw attempt. No one responded to that. Do you guys not even bother with self-drilling screws when it comes to drilling into SS?

You all mention (except 1) slow but my drilling at #1 setting, no more than half or so trigger is not slow enough?

Aside from the bit quality, I think the "feed"/pressure part is the part I need the biggest improvement. To understand in better detail, do I start off with lots of pressure or do I let the bit spin then increase to a maximum pressure point?


Thanks again!!

 

[CGarage]

How To Drill Stainless Steel — Complete Guide - Drillbitsworld.com

The definitive guide to speeds, feeds, bit selection, and preventing work hardening — for 304, 316, 17-4 PH, and duplex stainless steels

drillbitsworld.com

You need to center punch your holes, before you drill, too.

 

[RoninB4]

-Most important aspect to drilling any material: The drill bit needs to be sharpened correctly and stay sharp at the cutting edges.

-Even some new twist drills (and other cutters) I've seen weren't sharpened correctly by the manufacturer. New doesn't always mean it's good to go even though it should. If the drill is sharpened correctly you shouldn't need to lean on it too much to start cutting or go through an 1/8" plate. Those that claim slower speed isn't important don't know what they're talking about. Those that claim you need high feed pressure probably have dull twist drills that need sharpening. High feed pressure on thin plates has a good chance of shattering the drill when it breaks through the other side. Breakthrough requires a more delicate touch or a wood block backing.

-Work hardening is the biggest problem with 300 series stainless steel. WD-40 is ok for aluminum but not for steel, I'd sooner use motor oil than WD-40 for stainless, just dip the drill tip in oil every 3-7 seconds. I wouldn't let the drill just spin in contact with the material, you do need medium feed pressure right at the start. You're either drilling material or you're rubbing your way to work hardening.

-Your target diameter of 9/64 (.1406) shouldn't really need a pilot hole. Punch a decent dimple to locate and go full target size. The drill does need to be sharp and have the correct geometry or it won't cut well. Larger diameter holes do benefit from a pilot drill sometimes but there's rules/guidelines for that too.

-The self tapping screws have seldom given me confidence. There's a good chance that all that "bobbling" just caused the stainless to work harden because the self tapper didn't cut, it just rubbed.

-Half trigger is not a speed indicator. The color of the chip tells you the cutting condition. If the chip color is yellow you're going too fast. If the chip color is purple or blue you've already gone way too fast and have likely dulled the cutting edges. A re-sharpen of the drill is required. With twist drills you need to watch the flutes of the twist drill itself. If the flutes are starting to disappear then you're going too fast for stainless.

-I do realize that you're not a tradesman but drilling isn't a simple poke-n-hope process like some feel it is, especially in problematic materials like 300 series stainless. If your cutter is correctly sharpened and you follow the speed guidelines cutting/drilling SS isn't that big of a problem. Failure to follow those speeds, or have a dull cutter, is where almost all problems arise. Some reading will greatly help your understanding and your results. Asking questions is encouraged here.

 

[American Locomotive]

With small bits like that, there's really no need for a "starter hole". Stainless steel work hardens, so the metal that's being cut gets harder and harder the more it gets pushed around. So you drill a hole, now the edges of the hole are very hard, which makes it more difficult for the next bit. 9/64" is a small bit - just center punch, then drill.

I wouldn't bother with the self drilling stainless screws. They really won't be that much tougher than the base material, and will probably just gall and snap, and make things miserable for you.

Stainless requires a lot of tool pressure, and you have to commit to the hole. If you ease off, or ease into the pressure, the metal is going to work harden. The goal is basically to keep the cutting edge "under" the rapidly hardening metal at bottom of the hole and into the softer "untouched" stainless steel below it. If you back off on pressure, the metal will harden right under the bit, and then you have a problem.

"Going slow" is relative to the size of your bit. Materials have a certain target "surface speed" that they like to be cut at, and surface speed is a function of diameter AND RPM. For a 9/64" drill bit, you're going to be want to close to 1500 RPM for stainless, which is probably pretty close to the max speed on your drill (look at the sticker).

As others mentioned, hand-drilling stainless is really, really difficult. You really need to get the work into a drill press if possible. That allows you to apply steady, consistent, high pressure. That is difficult to do on a hand drill, and when you get close to the pressure you need, you're probably going to snap the bit.

 

[PoorUB]

Slow is nonsense. If you try to drill a 1/4" hole in 304 SST at 80 RPM you will get nowhere. But try.

You need good bits. Stainless is not hard but work hardens during drilling.

Slow is a relative term. For mild steel and a 1/4" bit you will run around 1,500 RPM. For SS and 1/4" bit that same RPM will screw you over, so maybe 300 - 500 RPM for stainless.

I have drilled a lot of stainless over the years and used good old HSS drill bits. If I know I will be drilling SS I will pick up new bits and not take a chance on a used bit, that looks ok. Like the other posts, high pressure and lube.

 

[CGarage]

Don’t forget the oil or tap magic or wd40 to keep the drill bit cool…..critical step!