TIPS FROM A PROFESSIONAL: HOW TO DRILL STAINLESS STEEL

If you are not used to it, stainless steel can be difficult to drill. You'll end up burning drill bits faster than you have time to change them.

How do I drill stainless steel? Drilling stainless steel requires sharp drills, low RPM, high cutting (feed) pressure and plenty of coolant. High RPM will cause the drill bit to burn up immediately.

Beyond that, there are a few other tips to help you get the job done, such as how to stay steady and how to choose the right drill bit.

REALISTIC DRILL BIT SIZES

Because stainless steel is a stronger material, it's important to be realistic about what size holes you can make with the tools you have.

If you're using a hand drill, you'll generally be limited to a size range of 1.6mm to 9.5mm. Anything larger or smaller than that will be of questionable quality.

On a drill press, the process is more stable because the setup is more rigid and the drill is aligned more precisely. Depending on the torque of your machine, you can drill some pretty big holes.

The point of all this is that if you need a 50mm diameter hole and you only have a cordless drill, get professional help. Or buy a ring mill.

HOW TO GET THE CORRECT RPM

Turning a stainless steel drill bit too fast is the most common mistake.

This can be tricky if you're using a hand drill, but most drill presses or other similar machines will give you at least a general idea of what RPM you're working at.

If you are using a hand drill, it will usually have some sort of marking on it indicating (at a minimum) the maximum RPM. This can give you a rough idea of how fast it is working.

The RPM of the drill depends on the size of the drill bit. The larger the drill bit, the slower it needs to be turned.

CHOOSING THE RIGHT DRILL BITS

Not every drill bit will work well with stainless steel.

To avoid stating what is already obvious, drill bits should be designed for metal, not wood or stone.

This means that you do not need to use spade drills, brad points drills, Forstner drills or impact drills. They are not designed for metal.

Even drills that say they are designed for metal may not be up to the task of making holes in stainless steel.

For example, I would strongly discourage the use of a simple carbon steel twist drill bit. The cutting edge will wear out in no time.

At the very least, use high speed steel (HSS) drill bits. Ideally with cobalt. They cost more, but they are much better for tough materials.

They perform better under high heat, which is common with stainless steel, and they dissipate heat better.

Pro tip: Not all cobalt drill bits are the same. They have different grades depending on their cobalt content. The M35 contains 5% cobalt and the M42 contains 8% cobalt. More cobalt means the cutting edges stay sharp longer.

USE COOLANT

Stainless steel is actually quite abrasive when cutting. If you drill it dry, the cutting edge will wear down very quickly.

Coolant helps keep the drill bit and workpiece cool. Stainless steel when overheated does what is called hardening.

Essentially, it causes a hard area to form at the bottom of the drill hole, and drill bits that come in contact with this hard area burn quickly.

One of the easiest ways to lubricate your drill bit is to apply some WD-40 to it while cutting.

Pull the drill bit out of the hole, apply some lubricant to it, drill for a few more seconds, rinse and repeat.

The minus of using WD-40 is that it is a very light lubricant, and it can make a lot of dirt.

Cutting wax works even better. It will stay on the drill longer and will leave virtually no dirt behind.

APPLY PRESSURE WHEN CUTTING

This point may seem a bit counterintuitive. Any time you cut metal, heat is generated.

There are three things that can get hot:

• The drill bit;
• The workpiece;
• The chips.

If the heat goes to the drill bit, the drill bit burns. If heat goes to the workpiece, the metal hardens.

However, if the heat goes to the chips, the heat is dissipated away from the cutting zone and everything works as it should.

One of the keys to success here (besides using a sharp drill bit) is to make sure the chips are large enough to withstand the heat. That means you need pressure.

Basically, if you don't apply enough pressure to the drill, the drill will rub rather than cut.

If you are drilling by hand or on a drill press, the main thing to pay attention to is the shavings.

When drilling by hand, the chips should come out in continuous spirals. It should not look like fluffy stacks of chips or dust.

It should look like this:

Not like this:

Normally stainless steel is not magnetic, but poor cutting conditions can cause it to become magnetized. If you see this, you need to double check the cutting pressure and make sure your drill bit is still sharp.

Cutting pressure does not mean that you are pressing your entire body weight on the drill bit. That would be dangerous.

In fact, you need to apply enough pressure so that the chips come out cleanly and don't generate excessive heat.

KEEP THE DRILL BIT STRAIGHT

This mostly applies to drilling by hand, but I've seen guys make mistakes on a drill press as well. Drills are not designed for lateral pressure, and stainless steel is really relentless. Pay special attention to how level you drill the stainless steel. Otherwise, the shank of the drill bit will rest against the side of the hole, making it oblong, and you risk breaking the drill bit.

If you drill by hand, the result of a broken drill bit can be painful. On the drilling machine, make sure that the drill bit does not deviate from the center or create side pressure. This usually happens when drilling an uneven or sloping surface. A simple way to correct this is to clamp the workpiece and start drilling the hole. Once the drill passes the angle of inclination, turn off the spindle. Release the workpiece and apply slight pressure with the non-rotating drill to center the hole under the drill. Then clamp the workpiece again and get to work. Drilling stainless steel is always a little more difficult than carbon steel, but if you follow these instructions, everything will go fairly smoothly.