Drilling Stainless Steel

[Curmugeon]

I have found that as well as drilling slowly with the best well lubricated drill bits, the most important thing was to use a punch to stop the bit "walking" and ensure the hole is in the right place to start with.

[Eight Sails]

As others have posted, drill slow. But what does that mean, exactly?

I recently needed to drill four 1/2" holes in 3/16" 304 stainless plate to make a pair of backstay extenders. I bought an expensive new Milwaukee cobalt bit, set the belt and pulleys on my benchtop Delta drill press to the slowest speed, which would still be about 700-750 rpm, and flushed the hole with cutting oil. The drill barely got through one hole before severe work hardening took its toll; after the second hole, the bit was too dull to cut at all. $40 CDN wasted....

I took the second plate to a machine shop. The machinist popped a freshly sharpened bit in his drill press, drilled two clean holes just like that, chamfered them with a rose bit and charged me for 5 minutes work. I asked him how he did it and he smiled and said "Go slow", so I asked "how slow is that?" and he said 150 to 200, your drill press is way too fast. I went home, re-sharpened the bit, put it in my trusty 1/2" corded drill, put the drill in a tool bag drill press attachment and tried again on some scrap, using the slowest speed I could get from the trigger. Sure enough, it drilled clean holes, as did a non-cobalt HSS bit I had lying around, after sharpening.

The moral of the story: "slow" means the slowest speed you can coax from your drill, around 150 rpm; your home shop drill press may not be slow enough and a high-torque, variable speed hand drill may be better; a dull cobalt bit is worthless but an ordinary HSS bit will do the job if its sharp; learn to sharpen the HSS bits you've already got and save the money, unless you've got enough holes to drill to justify the cost.

Your mileage may vary but that worked for me....

[djdeakyne]

In addition to the proven techniques already posted, I start with a small pilot hole and gradually increase the diameter until the correct size is reached.


The pilot bits break easily so stick them way up into the chuck, go slow, and look for the curly-q.

[Xlantic]

Originally Posted by coopec43

How to drill stainless steel

First of all you should read our 6 step guide to drilling through metal which will explain the basics of drilling metals.
A split point cobalt drill bit is the best choice when using a hand drill.
The split point prevents the drill bit from ‘walking’ or sliding.


Beware of too much heat

Probably the biggest problem which can occur when drilling stainless is for it to ‘work harden’. This happens when excessive friction causes too much heat build up. The result is that the metal actually becomes harder than it was in the first place. It is crucial that you avoid this happening.


You can avoid work hardening by

• 1. Drilling at a slow to moderate speed so as to avoid excessive friction.
• 2. Using plenty of drilling lubricant.
• 3. Applying moderate pressure – above all do not apply too much pressure.
• 4. Rest periods – allow the drill bit to cool down between drilling sessions.
• 5. If drilling a large hole then first of all start with a smaller diameter hole first and then work up gradually to desired size

https://www.ttp-hard-drills.net/dril...ainless-steel/

Yep, it’s the heat that hardens the SS. This matters a lot more than anything else, including the drill bit itself.

When drilling SS I use a water hose to continually cool the surface being drilled. That’s all it takes.

[CarinaPDX]

Good advice here.

I have used solid cobalt bits to good effect on SS but they are very expensive these days. More recently I have seen cobalt plated bits, along with the more common titanium plated bits; these will not last nearly as long and they can't be effectively sharpened but for a few holes they are an economical solution, and the one I use unless I have to drill a large number of holes. I am unfamiliar with the M42 bits so will have to look into them.

I learned long ago to start with a small(ish) bit (usually 1/4" with thick metal) and then progressively work up in bit sizes. This allows for high pressure without requiring a lot of force. Trying to drill a 1/2" hole in one pass requires too much force for a hand drill, and is even difficult with a cheap drill press. BTW never waste your money on a Harbor Freight drill press. Before I bought a drill press I looked at them and was pretty shocked. The vertical shaft was turning in a hole in the casting, no bushing present. These are not made to last very long, and would require drilling out and pressing a bushing in at some point. There are decent inexpensive drill presses available, although I don't know if they will turn that slow - I need to check mine.

Instead of cutting oil I use cutting paste. It is nearly the same thing because as soon as the drilling starts the paste melts into an oil from the heat. It is just easier to use on vertical surfaces.

Greg

[Ard Righ]

I have recently drilled two 10mm holes in a 10mm thick SS chain plate. I bought new 5mm and 10mm drill bits from the local general hardware store and I used a cheap battery drill. I drilled a pilot hole with the 5mm drill then followed up with the 10mm. I agree with the sentiments above and drilled as slow as I could with as much pressure as I could with regular application of cutting fluid. The hardest part was getting the courage to start.

[Icarus]

Cobalt drills, to drill into stainless they drill bit needs to be sharp, You need pressure to avoid surface hardening and cutting fluid.
I have a small pedestal grinder on the boat for sharpening drills, chisels and so on.
You als need to know how to sharpen a drill bit, I have a geared Bosh drilling machine to drill holes of up to 16mm diameter into metal.

[Icarus]

Correct
In addition a 6" small pedestal grinder for sharpening drills and so on is definite bonus.
A geared AC drilling machine for larger diameter holes is in my opinion is a must, variable speed trigger machines don't cut it.
BTW I am a tool and die maker

[coopec43]

Cobalt vs HSS

"HSS Drill bits are a more economical option in comparison to Cobalt Drill bits and is the most cost-effective drill bit type available. Making HSS Drills more suited for the general multi-purpose use activities such as small-scale DIY tasks. Cobalt being a more expensive option are typically used by professional construction users and trades personnel for specific purposes."
https://qlt.tools/blogs/ruko-shop-blog/cobalt-vs-hss

That's why I drive a Mazda and not a Mercedes!

[s/v Jedi]

Originally Posted by coopec43

Cobalt vs HSS

"HSS Drill bits are a more economical option in comparison to Cobalt Drill bits and is the most cost-effective drill bit type available. Making HSS Drills more suited for the general multi-purpose use activities such as small-scale DIY tasks. Cobalt being a more expensive option are typically used by professional construction users and trades personnel for specific purposes."
https://qlt.tools/blogs/ruko-shop-blog/cobalt-vs-hss

That's why I drive a Mazda and not a Mercedes!

Drilling stainless steel -is- a specific purpose for cobalt bits. The M42 bits are affordable.
HSS works when they are razor sharp, either brand new or sharpened for the task at hand. But they dull quickly.

[Mike Burch]

The chromium in stainless steel instantly forms a very hard transparent layer of oxide as soon as it sniffs any oxygen. Machining stainless therefore involves keeping the cutter below the surface layer. Allowing the cutting edge to merely rub will result in hardening even further.

In my experience (forgive the boasting, but it does stretch over more than half a century), you should NOT centre-punch the location of the hole, because that operation itself will cause hardening. The thin pilot drill bit you then try and start in the dimple will be in danger of breaking. The solution is to use a split-point drill bit. These have a 135° point instead of the usual 118°, and the two cutting edges of the bit overlap at the centre. Hence a split-point bit does not need a centre-punched dimple to locate itself in.

Many cobalt drill bits are advertised as solid cobalt, but that simply means that they are not merely cobalt-coated. It does not mean that they are nothing but cobalt. The metal is an alloy of steel with some cobalt in it. M35 tool steel contains some 6% cobalt (IIRC), and M35 split-point bits are readily available (and not at all expensive, especially the Chinese ones). I have a set in my shop, and they're used on stainless and in any other situation where centre-punching is not an option.

Having said that, I will confess that I have also drilled a hell of a lot of 316 stainless with ordinary HSS (high-speed steel) bits, always remembering the "plenties", viz.:

Plenty of sharp
Plenty of slow
Plenty of paste
Plenty of pressure.

I hate having to drill 316 by hand, especially if the drill is battery-fired. It's impossible to maintain a steady slow speed and a steady high pressure—push harder and the drill almost stalls out, so push a bit less and the darn thing whistles straight up to maximum revs. I do have an ancient geared-down single-speed mains-powered drill, but that thing has so much torque that when the bit inevitably jams in the hole, the drill does its best to fling me into orbit. But Sod's Law mandates that anything stainless on a boat is always firmly secured to several other things and cannot therefore be easily removed to be punctured by a large and hairy-chested drill press.

Good luck...

[GrowleyMonster]

https://www.amazon.com/HHIP-5000-001.../dp/B01M170ADF

A center drill to start your hole is a good start. If drilling freehand with a hand drill, it is super important to first of all make a good dimple with a center punch before applying the center drill, and second, keep the drill absolutely straight and true. I mean absolutely, even if it means buying one of those portable drill press twin rods and bushings and chuck fixed to a baseplate contraptions which are cheap, by the way. Along with the angle, keep your pressure consistent, also.

If you do seem to have work hardened the material, try another jab in the hole, with your center drill, with plenty of pressure and oil, and just peck at it a couple of seconds at a time. It should break up small areas of hardened material.

I have drilled quite a bit of 300 and 400 series SS with ordinary HSS bits. But you have to use plenty of oil, keep the drill absilutely straight and never waver, peck drill, and keep your bits sharp.

I use Marvel Mystery Oil, Tap Magic, Rigid, or any other oil at hand, and I would not even blush at using the dregs left over in an engine oil jug. It all works, just keep plenty in the hole to keep the bit and the hole cool.

By peck drilling, I mean going for a couple of seconds, and stopping, and clearing the bit flutes and the hole if needed, waiting a bit, and going another couple of seconds.

You should be making nice curly chips if all is well. If not, maybe your bit is dull. Youtube is your friend. Learn to sharpen bits and it will save you $ and frustration. I don't like those "drill doctor" contraptions. Rather do it on a well dressed wheel with a well made jig, and never the flimsy little tool rest that most bench grinders come with. You need precise control of the grinding angle on the cutting edge and the relief cut. This is a very handy skill to cultivate.

Cobalt, titanium, carbide "super bits" are fine, but ordinary HSS bits are easier to sharpen and way cheaper, and will handle most common grades of SS.

[Ard Righ]

I enjoy and value the advice given by many in this forum, but I want to make the point that I did successfully drill two 10mm holes in the SS chain plates. I did use a battery drill even though the speed control was somewhat intermittent as mentioned above. Removing the chain plates was not an option so I had little choice but to drill in situ. If your situation is like mine, then my advice is follow all the good advice and give it a go!

[Johan Leopard51]

Lots of the expected comments about bit and speed and lube - but what views on first drilling a pilot hole?

[Iron E]

Originally Posted by Johan Leopard51

Lots of the expected comments about bit and speed and lube - but what views on first drilling a pilot hole?

Mentioned above:

Originally Posted by Ard Righ

I have recently drilled two 10mm holes in a 10mm thick SS chain plate. I bought new 5mm and 10mm drill bits from the local general hardware store and I used a cheap battery drill. I drilled a pilot hole with the 5mm drill then followed up with the 10mm. I agree with the sentiments above and drilled as slow as I could with as much pressure as I could with regular application of cutting fluid. The hardest part was getting the courage to start.