Drilling stainless steel

I need to put a sturdy stop at the bottom of a very heavy (maybe 100 lbs.) wooden back gate I recently installed. The gate has a spring closing mechanism on it, but closing will also be wind assisted for much of the year, so it will close with considerable force. I had a nice piece of 3/32" stainless steel plate to mount to the 4x6 gate post, but when I tried to drill the holes it defeated every drill bit I tried. Some of the bits I tried were unused, so dullness isn't the issue. Is there any trick to drilling stainless other than having the right kind of bit? I'm at the part of my life where I don't want to buy any more one time use tools, so if the only way to drill this is to buy a high quality bit, I'll just deep six the stainless and make a new plate out of mild steel.

Stan

I've used Dewalt Cobalt Drill bits and they were the best of the ones I tried.

Drill with a regular bit at slow speed and with as much pressure as possible. If the bit squeaks your turning too fast. Oil helps too. A drill press is best of course, as long as it goes slow enough. By slow I mean VERY low rpms, 25 or so if posible.

A cobalt bit is best. Sounds exotic but they are available in various sizes at the big box stores such as Home Depot or Lowes.

I covered this a couple of times. Go to Fastenall and buy a couple of Viking bits. Very high quality. Next is if you are outside run a garden hose at a good dribble so you wash away the chips and keep everything super cool. Lastly........go VERY VERY slowly. You want so the bit is makeing one or two revz per second. Stainless will temper INSTANTLY and then you are totally screwed. Mild steel is a snap but stainless is what I just told ya. That is why competition rifle barrels are made from stainless and then cryogenic relieved. Also cost $400.oo plus per barrel. On a crome molly barrel you shoot it several hundred times till it is settled in and shoots very consistently. It polishes the inside of the bore. Stainless you shoot maybe a couple hundred and it is locked in. As you shoot it the brarrel gets a skin of tempered metal in the bore. After you get a stainless barrel broken in you treat all of your bullets with molibnium powder and they are super slick and consistent. The newest thing is coating bullets with powder coat paint. I haven't had a chance to try this yet. At work all of the cooking equipment is stainless and you need to drill really slow. One more thing. A drill bit salesman told me a secret. Use a few drops of straight antifreeze. Yup...a few drops, drill slowly a couple of seconds and then put a few more drops on and repeat. It really works. SLOWLY !!!!!

Yes,yes. People are so impatient. Slow means really slow and well lubed and cool. Stainless can be a total nightmare. Actually that is why some of the big industries use punch presses to get the holes. Stainless will punch almost like butter. But once you get it hot it is now tempered and nothing will cut it.

Hello Stan in oly,WA,

Drilling any material requires that speed and pressure are adjusted for the work. Stainless requires a lot of pressure. Speed can vary also, but 500 600 R.P.M.S is what speed is normally used for stainless, even on a lathe. If you are not using lubrication, you will not drill much of anything for long!. A cordless drill on low speed should work, as they are unusually rated @ 450 R.P.M.S. Also drill bit angle is important. Normal angle is 118* I like 138* because less of the cutting edge is exposed while cutting, less heat is then generated while drilling. I don't like motor oil as a lubricant for obvious reason. Away from a water source you can use a spray bottle, or a drip set up WD40 work too. Drilling a pilot hole is also a good practice. Good luck!


Guido.

As others have said slow RPM steady pressure and lube. You want to see a nice chip wind out of the hole and up the flute you dont want a bunch of gravel and dust comming out

The good drills from Fastenal work well, go slow, they make special lubricants for stainless, in a pinch you can use turpentine, but water would be better than oil.

Jon, I took your recommendation because you were the first person to suggest a way to do it with what I've got on hand, which is what I think I asked. Also, your advice is always good. I hauled out my Harbor Freight bench top drill press, washed the spider dropping off it, and set it for the lowest speed it would deliver---625 rpm. That's quite a bit faster than what you said, but still, it was out, so what did I have to lose? I applied moderate steady pressure and oiled the cut regularly. It worked like a champ.

Thanks.

Thanks everyone. Good information and good advice. If you didn't read my reply to Jon f mn below, I was able to drill the holes I needed by using my el cheapo drill press, lots of oil, and going slow.

Stan

When drilling stainless you don't stop halfway through or the spot work hardens and makes it almost impossible to drill. At Nabisco we drilled using Anchorlube. Partly because it was lard based and made for food plants but it was a good stainless drill lube.

I'm glad it worked for you, but I'm surprised it worked at that speed. I had to add a jack shaft to my drill press to get it slow enough for me. I doubt it turns at 100 rpms now but it works slick. What ever works is what I say.

When a problem comes up in a detail of a job that you're almost done with, you have to make a choice whether to put more time into solving that problem, or going back a step or two and doing it a way you know will work. Getting four 3/32" holes drilled was all I needed to finish that project, but if it was going to get complicated, I could always cut another piece of mild steel plate (with a cut-off wheel on an angle grinder), grind the mill scale off it, polish it, and drill my four holes in it. That was probably at least half an hour's work, so that was the most time I wanted to put into getting the holes through the stainless. So I was glad it worked; by the time it did, I had another half hour invested anyway.

Stan

That is a small hole so the speed was close. Again, glad it worked for you.

Our company makes stainless alloy castings in a number of different compositions. Machining difficulties are some of the biggest complaints we get from those who don't normally work with these materials.

A great example of how difficult they can be are some items we make under National Stock Number parts for military applications world wide. These are 316 stainless high security hasps that are used on ammo locker doors to deter theft. These go by the name NAPEC hasps which is an acronym for Naval Engineering Production Engineering Center.

The intent with these is not to assume someone can't cut through them but assure that it will take them a long time to get to the $1,000 padlock that is shrouded inside them.

I have attached a link to our webpage that shows these.
NAPEC Hasp