Drilling through stainless steel

[Terra Nova]

Small drill bits often won't take the high pressure required to start a hole in stainless, especially 316. Instead use a cobalt center drill to first get a small hole through the tube's wall. It is stubby and will withstand immense pressure without snapping.

[a64pilot]

Your all correct, however this is just tubing, go slow with lots of pressure and he will be fine.
What happened I’m sure is he let it get hot, that tempered it and then it’s like trying to drill diamonds.
We all have done it at one time or another.
The funny thing is SS is a soft, not particularly strong alloy, why is it such a bear to drill.

[Terra Nova]

Originally Posted by a64pilot

...SS is a soft, not particularly strong alloy, why is it such a bear to drill.

It is not soft, particularly after work hardening it by polishing.

[a64pilot]

My automatic center punch makes a nice divot in it, much more easily than hardened steel. But I’d rather drill through hardened steel.

[oleman]

Originally Posted by Woodland Hills

I am surprised that no one has recommended carbide drills over cheap cobalt and titanium oxide drills. They are much harder and will stand up to hard usage much longer.

Carbide is the correct drill material for hard metals BUT:

Carbide bits are generally used in milling machines with the material clamped to the table. They are so brittle that few techs can use them even in a normal drill press without having them break and that is especially true if attempting a hand drill and a small diameter of less then .1875". If you now have to use carbide, buy extra bits to cover breakage!

Once SS is worked hardened, either start a new hole or take it to the milling machine and use carbide.

A great material for cutting fluid is known as assembly lube used for sleeve bearing installation in engines. It has the consistency of cow slobber. It is my go-to lube for using a hole-saw to cut larger holes in thicker steel. It will double the life of a bi-metal saw in 1/2" steel hot rolled plate.

[CLady]

Use some cutting oil. It really helped when I was drilling 5/16" holes through 1/4" stainless steel plate.

[1950]

I use water for a coolant. Works very well and surfaces are clean when job is done. Use fresh water not salt. The chloride in salt water will react with the stainless.

[Cadence]

Originally Posted by Bigjim

My transom swim ladder is made of hardy stainless steel tubing. It does not have wooden steps or rungs. So, it is difficult to climb out of the water.



I purchased some teak steps but when I tried drilling the holes for the machine screws the steel burned out two drill bits, a normal steel bit and a cobalt bit. I then bought a titanium one but it fared no better.

Anyone have a suggestion on what type of bit will work with this sturdy tubing?

Drill about as slow as you could with a brace and bit.

[sailortype]

I was recently into the local jobber asking about bits to drill stainless. As it happened, the guy next to me was the floor manager in the local SS fabrication shop and he said they use nothing but cobalt bits.

[Nicholson58]

Originally Posted by RaymondR

Drill with low RPMs and with as much pressure as you can apply. Stainless steel has a low coefficient of conduction for heat and air quench hardens if you heat it up whilst drilling. If this has already occurred you may have to drill a small pilot hole and open the hole out with a couple of smaller drills.

Yes. Low rpm. Very sharp bit. High pressure. Cutting fluid will help.

SS and aluminum both will gum up a hot tool run at too high a speed.

Drill a small pilot hole and enlarge it.

[Woodland Hills]

Originally Posted by oleman

Carbide is the correct drill material for hard metals BUT:

Carbide bits are generally used in milling machines with the material clamped to the table. They are so brittle that few techs can use them even in a normal drill press without having them break and that is especially true if attempting a hand drill and a small diameter of less then .1875". If you now have to use carbide, buy extra bits to cover breakage!

Once SS is worked hardened, either start a new hole or take it to the milling machine and use carbide.

A great material for cutting fluid is known as assembly lube used for sleeve bearing installation in engines. It has the consistency of cow slobber. It is my go-to lube for using a hole-saw to cut larger holes in thicker steel. It will double the life of a bi-metal saw in 1/2" steel hot rolled plate.

Don’t tell anyone at Boeing or McDonnell-Douglas that carbide is only for milling machines: we used them all the time in hand drill motors for rivits and hi-locs on all sorts of materials. Only the tip of the drill is made from carbide, the shank is the usual HSS like any other drill.

[jmschmidt]

Can't add much here except I bought a set (1/16th to 3/8ths in 1/64th increments) of some cheapo Taiwan made titanium bits being sold on the side of the road 40 years ago for $15. The ones I haven't lost or broken still cut SS like magic if your follow the rules others have mentioned here. Can't find any thing today even close unless you are willing to pay $100+. And my cheapo Taiwan drill press I bought at the same time is still working great.

[Cadence]

Originally Posted by Terra Nova

It is not soft, particularly after work hardening it by polishing.

That's it! The bits don't necessarily go the SS surface gets hard.
then the bits go. Faster may be better for a lot of things, drilling SS isn't one the other may be in bed.

[roverhi]

Someone has been trying to sell a drill guide for round tubing on Ebay. Looked like a must have if you are drilling SS round stock without a drill press.

Other than that slow speed and pressure with a cutting oil are the way to go. Stainless work hardens in a split second if the drill bit skips.

[S/V Alchemy]

Originally Posted by RaymondR

Drill with low RPMs and with as much pressure as you can apply. Stainless steel has a low coefficient of conduction for heat and air quench hardens if you heat it up whilst drilling. If this has already occurred you may have to drill a small pilot hole and open the hole out with a couple of smaller drills.

Yep. A torquey drill helps, as does punching in a starter divot and working your way, slowly, up the drill bit sizes.