Drilling Stainless & Aluminum

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How do I Drill holes in Stainless Steel and or Aluminum? I am changing my traveler bar and this means I have to drill new holes in the Stainless Steel Plate just below the fiberglass where the traveler mounts. How do I drill Stainless? Drill Bit? Drill Speed? Lubrication? Any experts out there?

Capt. Al, Kindred Spirit #55

Stainless Steel Drilling?

  • I know from experience a normal (even expensive) bit will not drill stainless steel. You will need a carbide tip drill bit. I know you want to keep the temp down on the steel so lots of cutting oil many breaks if you are drilling thick stuff, etc. Not sure of what speed to use.

  • I've done this. The plate embedded in the 'towers' is not stainless, it's either brass or bronze (at least on my boat, #52, 1986). As with any metal, a little cutting oil doesn't hurt. Just about any bit rated for metal cutting will do as long as it's sharp. Bob Mack, Upon A Star #52,

  • Stainless steel is a pain to drill, but it helps if you follow the tips I've learned from experts. Get hold of some cobalt bits; expensive, but worthwhile. Ordinary HSS (High Sped Steel) bits will dull too quickly if used for stainless. Also, obtain some cutting oil; do NOT be tempted to use WD40, the experts tell me that it 'runs away' from the hole as the work heats up. Start with a small-than-required bit size, and use very slow speed and a lot of pressure. As the hole begins to break through, lighten up on the pressure and speed up the drill. Then switch to the larger bit size and drill again, using plenty of cutting oil. I've successfully used my Black & Decker 9.6-volt cordless drill for drilling stainless, but it's a lot easier with my big Sears line-powered variable speed drill, which has an orthogonal handle that makes it easier to keep straight.
There's a bit of a controversy about the use of a center punch. Some say that it 'work hardens' the material. I personally think it's about the only way to keep the bit from walking away from the marked spot. There's nothing more infuriating than drilling a hole, which is too far off center to attach the thing you were planning to attach!
Be sure to trap and clean up any particles; while they won't rust, you WILL be generating lots of sharp little shards of material that will wind up painfully embedded in the soles of your feet if you aren't careful!
Norm Bernstein, Amoreena, C400 #105

  • Stainless grade steels are extremely soft due to the chrome and nickel content. The more stain resistant, the softer the material. You need to use extremely sharp tools to machine stainless, as the biggest problem is build-up of material on the tool causing the tool to overheat and dull out quickly. Lots of oil for cooling is also important. Tool speed and feed speed can be determined with observation of the job. Higher tool speeds are usually the best policy with a slower than normally used feed speed that would be used to machine less stain resistant steels. Ron Euler, Gone with the Wind, Naples, FL

  • I have worked with stainless steel for many years and what I find works for me is this: Prick punch the spot first or the drill may wander before it bites into the steel. Then size a pilot bit using the web across the desired bit's end, right at the peak. This way the boring bit starts cutting using all of the cutting surface making it easier for the bit to cut without wandering. Use a cutting lubricant if possible and keep your speed low if you are cutting a large hole as stainless tends to heat up, expand and bind. If you allow stainless to get too hot it will harden it making it more difficult or next to impossible to drill, i.e. letting the drill bit get red hot before stopping to sharpen or replace the bit. Stainless steel is softer that carbon steel and will wear out drill bits very quickly if proper procedures are not followed. These same techniques work for aluminum as well. Gary, Wind Spirit C30 #1544

  • I hope you saw my reply to a post a couple of days ago about drilling SS to a larger daim. The full story is much longer than the following, as there are precise conditions for every material, but I hope I can give you a few ideas to help outside a machine shop. Remember to reduce heat as it tends to destroy the "stainless-ness" of SS, type 304 more than the true marine grade 316. SS can be cut and drilled, but it is hard stuff and needs care. The optimum is to have the work and the bit brought together in a drill press or some other machine that gives you control. The key to drilling or machining any metal is control of all factors. Always use a centre punch at the start to prevent wandering of the bit. If your final size is more than about 1/4", follow the punch with a pilot hole, which should be the same diameter or a tiny bit larger than the web (the centre or area that joins the two cutting flutes of the drill bit) again to ensure that the drill does not wander or chatter. e.g., a 1/2" bit should have a pilot hole of about 1/8". Avoid the use of progressive sizes in hard materials as it is hell on the bit and the SS.
Because of the hardness of the SS, do not allow the drill bit's cutting edge to "mildly" to scrape, rub or cut the SS or it will quickly blunt the drill and further work harden the SS, making it almost impossible to drill again. Drilling SS is a pretty brutal process; when you get going, have immediate, continuous, strong, even, correct angle, speed and steady pressure on the drill and pour on the cutting fluid, which is as much of a coolant as anything. The bit is under great stress and will otherwise heat up rapidly. You may need to stop and let it and the SS cool or actually replace the bit before continuing. Use good quality bits, as they are still cheap compared to the hassle of dealing with an incomplete or poorly cut hole.
Unfortunately I do not have my data with me but the speed of drilling any material varies inversely with the diameter of the hole. If I recall correctly, a typical 1/16" bit should turn at something like 20,000 RPM, but that is optimum and few electric drills or presses can even achieve that. Likewise a 1" bit is down below 100 RPM I think. I believe that in SS a 1/8" diam should be about 2000 RPM but a 3/8" diam drops to about 500 RPM. Maybe an engineer on the list could make this more accurate. However, on a hand-held electric drill, you just have to use you best guestimate anyway. Check the full speed of your electric drill and go from there. When holding the drill, brace yourself firmly yet comfortably using elbows, a friend etc, so that you are rock steady, can exert reasonably strong feed pressure – and will not be hurt when the bit goes through or if it breaks.
I highly recommend a "high tech" cutting fluid called Rapid-Tap that I used for years in industry. It is just amazing stuff and quite inexpensive for the amount most of us would use. It seems to break down the surface tension of the cutting operation which in turn prevents heat build-up, allowing you to cut longer, and extends the life of your bits many times over. It may damage paint so be careful of that. It is not quite the same stuff as the traditional cutting fluids. It is like paint thinners in consistency; makes a huge difference.
Richard Britton, Friendly Dragon, 1976 C30 New Westminster, B.C.

Aluminum Drilling?

I am thinking of mounting a winch on the mast and this means I have to drill new holes in the Aluminum Mast. How do I drill Aluminum? Drill Bit? Drill Speed? Lubrication? Any experts out there? Capt Al, Kindred Spirit #55

  • You asked about aluminum. You should have no problem with a wandering or chattering bit - if you have a small pilot hole. The standard bits tend to grab soft metal and jam - ever tried to drill lead?! If you need to drill a lot of holes, and/or larger holes, the following very brief description may help you. Softer metals like aluminum, copper etc do not need a "chisel-like" sharp edge on the bit, but material should be removed by more of a scraping action. To get this, sharpen the bit in the usual way, but then (and it us against your instinct to do this!) grind the cutting edge so that the inside surface of the flute has a tiny face that is in line with the length of the bit, i.e. "straight up" the drill. So this will leave you with the normal angle of the drill under or at the end of the drill, but a scraping edge making contact with the material from where the swarf (waste material) exits. Use regular speeds, and I think you are unlikely to need cutting fluids, though I believe in optimum conditions you would.Good luck and I hope this helps. Richard Britton, Friendly Dragon, 1976 C30 New Westminster, B.C.

  • I have a main with reg. battens and a full batten main. I have no problem raising either one with my "home made" lazyjacks. To mount anything on the mast or boom drill and tap the hole so the item (ridged vang, whisker pole track, winch etc.) can be secured properly with a threaded stainless fastener. Start with a center punch. The hole should be 2or3 drill sizes smaller than the bolt. The tap usually tells what size hole to drill for. Use a little 3in1oil as it will keep the drill bit sharp. Use medium speed and medium pressure. The aluminum alloy is soft and easy to drill thru. Invest in a GOOD tap holder - it will make the job much easier and have a nicely threaded hole. When mounting the item make sure you put some anti seize or grease on the threads. Ron Hill, Apache #788

  • I'll give you a tip. It'll cost you about 18 bucks though. For your aluminum, always use some sort of punch, and go out and get a set of Black and Decker Bullet bits. They are the easiest way to make round holes in Aluminum, in my opinion. Otherwise it's easy to end up with triangles, and especially if you are tapping holes, that's bad. Tom