Drilling Stainless Steel

I need to drill a 30mm hole through a 4mm plate without the result looking like a beaver had a go at it. Tungsten Carbide or Titanium tipped/coated saws, wil either do it or is one better than the other. Cheers

That is a big hole. When I drill S/S i usually use cobalt bits and go slow with a lot of pressure and lots of cutting oil so it doesn’t get hot.

Try to find a TiNi step drill - a la Unibit - and the biggest pilot you can in cobalt or carbide.
A cobalt bit that size will be spendy but work.
If you have access to a quality drill press with a vise you could use an adjustable bit
with a carbide insert.
A machine shop would probably just use a punch press.

Or maybe take it to a machine shop. It might be about as cheap as buying a special bit for a one time deal.

I’m with Comodave.

I wouldn't attempt it without a drill press. I had the good fortune of having access to our machine shop at the airport so the mechanics were a great help in building my windlass/pulpit components.

Like Comodave suggests, find a local machine shop. Easy job for them. Same goes for polishing SS plate.

4 mm = less than 3/16"
30mm = about 1 3/16"

Nothing I wouldn't tackle on my Chinese drill/mill with a Unibit.

The key is slow turning bits and lots of cutting oil. Then a cut that without the proper care would get hot and never be accomplished, will be like cutting through butter.

I know this after mounting my davits, 1/2" holes in 1/4" material.

Had an 5" outside diameter circle cut with 1.5" hole in the centre in a 3/16" S/S plate by our local CNC shop, think a big washer. Super easy, fast and inexpensive..........

You can do that with a hole saw, even a high speed steel one. Getting enough pressure on it to cut is the key, your own weight on a drill motor will not be enough. A HSS annular cutter like is used in mag drills would be ideal. Or a machine shop. A hole like that can be interpolated on a CNC mill in about 30 seconds, and it will be round and on dimension.

DDW said:

You can do that with a hole saw, even a high speed steel one. Getting enough pressure on it to cut is the key, your own weight on a drill motor will not be enough. A HSS annular cutter like is used in mag drills would be ideal. Or a machine shop. A hole like that can be interpolated on a CNC mill in about 30 seconds, and it will be round and on dimension.

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I have seven holes through my 1/2" 316 SS stern plate that size, done with a hole saw and an oil can with cutting oil to keep it lubricated. Slow drilling, keep your drill speed low as well, but it will leave a nice clean hole.

One thing I did do, was after drilling the pilot hole, turned the bit around in the can so it didn't wallow out the pilot hole while drilling for such a long time. Milwaukee cans, nothing special about them, got multiple holes per can before they went dull.

That's a little over an inch, the Milwaukee hole saws with hardened teeth , slow speed and lots of oil will cut right through. A press will be best because if the hole saw "bites" with a half inch drill it will rip your arm off.

pete

"Getting enough pressure on it to cut is the key,"

YES

Ask around , somewhere there is a drill press you can use for 5 min.

Machine shop. Might charge you 40 bucks and won't make a hash out your plate.

Drill a small hole first, then use a knock out punch, 30mm shown. $15 on Amazon. It leaves a professional looking hole. Drill a series of holes until the bolt will go thru.

As others said, when drilling ss, lube, light pressure and don't force the bit.

Phil23 said:

I need to drill a 30mm hole through a 4mm plate without the result looking like a beaver had a go at it. Tungsten Carbide or Titanium tipped/coated saws, wil either do it or is one better than the other. Cheers

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A lot orf good advice for a piece of stainless not already attached to the boat.

Personally, I have found using oil on the bit, to make a lot of difference, when trying to drill stainless.

But, I agree, that sometimes, it can easier to just take it to a professional, and say "drill this, please".

I grew up on a farm, and we were constantly taking broken bits of equipment to the welders for repair. I asked my dad once, why we didn't just buy some welding gear.

His response was, you can buy yourself a welder, but you can't buy yourself twenty years experience in knowing how to use it.

For some reason people think SS is hard. It is actually very soft. That’s why SS screws strip so easily. It only gets hard with heat. Keep everything cool and you are ok to use a good hole saw. If you want it perfect you must undersize it then rotary file it. Most hole saws wobble a bit

Try a 35 deg drill at 12-14 RPM.

Arc said:

For some reason people think SS is hard. It is actually very soft. That’s why SS screws strip so easily. It only gets hard with heat. Keep everything cool and you are ok to use a good hole saw. If you want it perfect you must undersize it then rotary file it. Most hole saws wobble a bit

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Stainless is strange to drill. You can be drilling with no problem and suddenly the stainless will harden and become undrillable.
I don’t know if it work hardens or heat hardens but it happens fast with no warning. I’ve drilled a lot of stainless and had it happen rarely but it has ruined a few pieces for me. Might be my fault, I tend to grab what ever oil is handy. Maybe a better cutting oil would have prevented the problem.

If you do this by hand, use a drill with a clutch to prevent jamming. As someone said, when the bit binds, it will break your wrist. We have a big Dewalt at work and at the first sign of binding.....it cuts out. Its a great safety feature.

306 is pretty soft and 316 is much harder, the chips from a hole saw with 316 are very small and clean. 306 gums up the teeth on the can. A side handle on your drill is a must if you are going to use a hand drill with a hole saw.

My fabricator used a mag drill, which magnetically holds the drill in place. A piece of ferrous steel under the stainless project will allow the magnetic drill to lock in place.

Arc said:

For some reason people think SS is hard. It is actually very soft. That’s why SS screws strip so easily. It only gets hard with heat. Keep everything cool and you are ok to use a good hole saw. If you want it perfect you must undersize it then rotary file it. Most hole saws wobble a bit

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Having been a machinest/tool maker in a past life, I found the above advice to be right on.

Most have hit the problem on the head.
And I reiterate the rules.
Only use sharp cobalt bits. Other bits dull quickly, you apply more pressure , heats the part, case hardens. your dead.
Lots / constant lubricant/ coolant
Steady / constant pressure/ constant cut.

Go to fast and heat the tip the stainless case hardens,,, your dead.

If I remember correctly, you should be able to use a Lennox Hole saw if you cut a core out of a sponge that fills the inside of the hole saw. soak it with Stainless Steel cutting fluid.

Drilling stainless

Maintain the cut with steady pressure and a sharp bit. Lose the cut and spin without cutting a chip and you will burn the metal blue and harden it rapidly. Of course coolant is a must.

Cobalt bit, slow, plenty of lube. Just like docking.....slow is pro!

Phil23 said:

I need to drill a 30mm hole through a 4mm plate without the result looking like a beaver had a go at it. Tungsten Carbide or Titanium tipped/coated saws, wil either do it or is one better than the other. Cheers

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Cobalt tipped drill bits are what's traditionally used for drilling stainless in the marine industry.

For a 30 mm hole in 4 mm stainless plate, I would find a shop that does plasma cutting. Shouldn't take them more than a few minutes once it is set up. Plasma makes a pretty clean cut in any conductive metal including SS.

David

same advice as prior posters use cobalt bits with lube pressure low rpm slowly. Don't overheat. Harbour freight sells a nice cobalt set relatively cheap if using a coupon etc.http://https://www.harborfreight.com/cobalt-drill-bit-set-115-pc-61886.html?_br_psugg_q=drill+bits