Drilling SS question.

[Cheechako]

Too big a hole for a cordless drill. Use a good corded drill and be careful about grounding! I would use a "Center drill" to start the hole... if not finish it. These are intended to stay on track well. If not a center drill then drill a pilot hole, maybe 3/16 or so. then go for the final 3/8. The more steps you take the more you risk work hardening and having problems. Use a variable speed drill and start slow. Its a matter of speed and how much you feed (push). at the right feed and speed you will feel and see the chips cutting "just right". too fast rpm and you will immediately work harden the surface and destroy the bit.... and that hard surface will likely destroy the next bit also. Cobalt bits for sure.

[delmarrey]

The last four posts are right in the ball park. The main thing is not to let the SS get hot unless you can keep the drill moving. IAW's If you're hand drilling start out small and work your way up keeping a chip flowing. If you can run water over the hole while drilling, that is the best method. The problem with hand drilling, is hole drift. If you need precision then a drill press with a center-drill starter.

Also, if you don't have the split point, you will have to drill a pilot hole.

Oil only acts as a lubricant and so so good for SS unless it stays fairly cool. Go slow if you can't use water!

After 45 years of machining SS and other exotic metals it a no brainer.

[bobofthenorth]

Originally Posted by 40 South

..... don't apply too much pressure.

Extremely bad advice. Apply as much pressure as you possibly can given the bit diameter.

The problem with machining SS is work hardening. Google it for a more complete description but the fundamentals are "as long as the tool keeps cutting you have no problems; the minute it stops cutting you have a huge problem." So the right speed for the bit - ie. not ridiculously slow but not the fastest speed you have for big holes. And steady firm pressure to keep the bit cutting. It goes without saying the bit should be sharp and you should use some tool oil.

And I'd probably go to 3/8 in 3 steps but you could do it with a pilot hole and a 3/8 bit if you've got good bits.

[Marksman]

I think three cuts (1/8 pilot, 1/4, 3/8 final) would work the best as the cutting edge of the bits will have enough contact surface you won't bury the cutter in the work and stall, but small enough not to require too much feed pressure to make a chip, compromising angle accuracy with your hand drill. For example, if you are only taking 1/32 steps, it will be easy to use too much feed presssure and the bit will bite deep causing it to self feed to the point it WILL work harden the big fat chip it's forming, bind and likely snap the cutter off. This will ruin your day. The other extreme is to pilot with a 1/16 and then go straight to the 3/8. This will require mucho grande tool pressure to maintain a cut without the bit skipping off, leaving a partial chip, also now work hardend and the bit will have trouble restarting the cut. My experience in a nut shell. Not a machinest but have drilled many holes and learned the hard way.

[captain58sailin]

I would listen to the machinists. I used to work with an old Man that could hand grind drill bits for drilling stainless steel. He would take an ordinary high speed drill bit and reduce the angle of the cutters and they worked very well on drilling stainless steel. Unfortunately, I never learned exactly what angle he was using or learned how to dress a drill bit by hand. I would also recommend using a slow speed, keeping the bit cool, lots of oil/water, steady moderate pressure, and at least 3 maybe 4 steps. I use a 1/2" Makita worm gear drill for good torque at slow speeds, you have to watch out though if the bit hangs up it can twist your wrist.

[Jim Cate]

FWIW:

IF you really want to have a sharp new drill bit for each hole, I would suggest that instead of buying a slew of expensive cobalt drills, you buy one and a drill sharpening fixture!

Not only will you save money on this job, but you will always be able to sharpen your bits when required in the future.

And I too believe in high pressure and slow speed for drilling SS.

Cheers,

Jim

[foggysail]

I have found just plain water lubrication works well drilling SS. For one thing, using plenty of water will keep the bit from overheating. As others stated, use a good sharp bit.

[sailvayu]

As the others said use a steady steam of water, slow speed, do not let the tip get red hot. For 3/8" I use a 1/8" pilot then straight to the 3/8" No need for expensive bits just a decent quality bit. take your time and keep the RPM low and a steady flow of water, it will be like drilling mild steel. I use a grinding wheel to sharpen but you should be able to drill all for holes without having to sharpen if you do not let the tip get hot.

[sabray]

Originally Posted by foggysail

I have found just plain water lubrication works well drilling SS. For one thing, using plenty of water will keep the bit from overheating. As others stated, use a good sharp bit.

Right on from my experience with all new chainplates. Used regular bits and sharpened as needed. Sharpening on. Grinder is easy. kobalt bits break and are pricey. Done both ways but water and regular bits was best. I did have a drill press and did not predrill. some holes were 1/2 inch. That's my experience.

[delmarrey]

Originally Posted by captain58sailin

I would listen to the machinists. I used to work with an old Man that could hand grind drill bits for drilling stainless steel. He would take an ordinary high speed drill bit and reduce the angle of the cutters and they worked very well on drilling stainless steel. Unfortunately, I never learned exactly what angle he was using or learned how to dress a drill bit by hand. I would also recommend using a slow speed, keeping the bit cool, lots of oil/water, steady moderate pressure, and at least 3 maybe 4 steps. I use a 1/2" Makita worm gear drill for good torque at slow speeds, you have to watch out though if the bit hangs up it can twist your wrist.

On a Colbalt drills the angle is 135º included w/a split point, and Tool Steel drills it's 118º included. BTW drills are not made of high speed steel, it's more brittle then colbalt.

It's when the drill is breaking thru the opposite side is when it gets the most damage, either chipping or burning.

[Hoohaa]

Thanks everyone. Wow. All this info is great, I think I will drill in 3 stages and buy cobalt bits standard bits and or look at the price of a drill sharpener.
Will also take a look at my old Bosch electric drill, I think I can wind it down to run fairly slow with plenty of tork.
I will let you know how it went on Tuesday.

Thanks.
Jeff

[Blue Crab]

You gotta love an internet forum. Except for the newest of the new, I'd guess all of us have had to drill some stainless. I'd have thought this would be a simple question but nooooooo. High pressure, low pressure, oil, water, corded, cordless, cobalt, hss, two stage, more? Yow. Work hardened ... yep been there.

I'm going with the machinists. I once watched a machinist pull out a 1/2" steel bit. He waved it at a bench grinder, then drilled thru a 1" steel plate in less time than it took me to type this.

[Wotname]

Just to throw one more technique into the mix but first a warning; not all machinists know this one and almost all the rest of won't know it; however it was a very old and experienced machinist who demonstrated it to me.

You know when drilling a larger hole from an existing smaller one and there is not a lot of difference in the size, the drill often chatters, grabs and is hard to control, well, here's the solution.

Take a small swatch of cloth (just a corner of a piece of rag) and maybe fold it once or twice if it is a bit thin. Say about 1" square(ish) for a 3/8" or 1/2" hole and the thickness of denim. Wet it with cutting oil (or water or kero or detergent), place over the small hole, press the larger drill bit against it and start drilling. Yes, start drilling with the cloth between the work and the bit. All the chattering and grabbing etc vanish. The cloth disintegrates in seconds but does not need to be replaced unless you remove the drill from the work before the hole is completed.

Sounds too simple or too good to be true - that is what I thought when I first heard him tell me - I assumed he was taking the p*ss until he demonstrated it to me - now I am a convert. Of course you still have to take all the other precautions as listed in above posts; it ain't a silver bullet but it is a bronze one

I have told a few expert metal workers about it and was laughed at until they tried it themselves.

Well now it's on CF so it must be true

[Blue Crab]

Wot?

I tried this inadvertently with a shirt tail once. Too bad it's not on video.

[boden36]

The best drilling and tapping fluid I have ever used is called "Tap Magic" . You should be able to get on eBay or large engineering supply shops. I have quite a few cutting lubricants in the workshop, and nothing comes close.

Regards,
Richard.