The Ultimate Guide To Drilling and Tapping Stainless Steel

Stainless steel is a versatile material that is well-known for its durability and anti-corrosive characteristics. As a result, it is one of the most common materials for building, DIY projects, decorative elements, transportation, and storage.  

However, stainless steel can become hot and challenging for drilling and tapping if your cutting tools are not used properly. If you have been working with stainless steel for a long time, you will know that high speed and brute force may not work well when using stainless steel. 

Why is Stainless Steel Harder to Drill and Tap?

If the cutting speed (RPM) is too high and the feed is too slow, the drill will rub the stainless steel instead of cutting it, generating heat and toughening the work material. This toughening of stainless steel due to heat is a phenomenon known as work hardening. 

Eventually, the drill will have to work harder, which will reduce the lifetime of the drills you are using for stainless steel and increases the risk of breaking. Work hardening also applies when tapping stainless steel by hand. 

The heat will concentrate on the side of the stainless steel taps making it harder for you to turn it. In addition, chips will accumulate and clog your stainless steel tap, leading to tap failure and breaking.  

Employing the correct techniques 

Although stainless steel is not as hard as high carbon steel,  tapping stainless steel by hand or drilling stainless steel using a power drill can be challenging if you do not use the correct tools and techniques. Successful drilling and tapping of stainless steel boil down to four factors: 

• Preparation, 
• Material, 
• Technique
• Speed. 

Preparation

Before drilling, you must first determine the size of the hole required for the eventual tapping. The drill hole should be smaller than the bolt diameter because the tapped threads will increase the diameter of your hole. Once you've determined what size hole you'll need to drill and tap, you'll need to mark and measure the location of your hole. 

Because safety is essential, you must ensure the following before drilling and tapping:

• Use personal protection such as safety goggles or a face shield.
• Maintain appropriate ventilation by keeping drill air vents free.
• Do not use a dull drill bit or tap.
• Keep any cords away from the cutting area while you're operating the drill.
• Never attempt to adjust the drill chuck while the power is switched on. 
• Tighten the chuck firmly and retrieve the chuck key before turning on the drill.
• To restrict movement, secure the object being drilled in a vice or clamp.
• Drill at the correct RPM depending on drill bit diameter and material.

Choose the Right Tools and Materials

Having the right materials, such as drill bits and taps, is critical when drilling stainless steel. It will save you money on broken parts and uneven holes and speed up the work.

• Twist drills/HSS Drill bits 

High-Speed Steel bits or twist drills, are designed for stainless steel and can be machine or hand drilled. It is recommended to use a Titanium tipped HSS bit because it decreases friction, minimizing work hardening produced by high heat. It also reduces flank and crater wear.

• Cobalt Drill bits

Cobalt drill bits are created specifically for heavy-duty use on high-tensile metals such as stainless steel. Cobalt boosts strength and considerably improves the heat resistance qualities of steel. 

Heat resistance to friction is crucial in drilling stainless steel because it reduces the work hardening rate. In addition, cobalt drills provide strength to prevent bit breakage as well as flank and crater wear.

• High-Speed Steel Taps

Hand taps and machine taps create internal threads in holes, allowing a bolt to be screwed into them. You should select your tap based on the sort of material you'll be threading into. For example, carbon steel taps are commonly used for softer materials, while high-speed steel taps are used for more rigid materials such as stainless steel.

Use Correct Technique and Speed

Many individuals drill at a faster rate, believing this will give them the right finish and will speed up the process. However, it does not apply to stainless steel because it hardens pretty quickly when heated during high-speed drilling. When the stainless steel has been hardened, drilling will become incredibly difficult. This is why it’s best practice to drill at the slowest possible speed.

Excessive pressure has the same impact as high-speed drilling, in that it causes undesirable heat buildup and work hardening. Instead, begin with light pressure and gradually increase it until you produce lovely spiral cuts emanating from the cutting face.

How to Drill and Tap Stainless Steel

Since stainless steel is a very hard material, you have to choose the right twist drill. The twist drill should belong to the application group Type H of the DIN 1386 division. Over time, however, mixed forms have been developed whose naming systems are not standardized in the DIN manual. So you will find at RUKO for the use in stainless steel the types VA, FO, UTL3000, UNI, TL3000, N and UTL.

In order to cut stainless steel, your twist drill must

• be made of tool steel HSSE-Co 5, HSSE-Co 8 or solid carbide,
• have a large point angle (e.g. 130-135°),
• have a small spiral angle (e.g. between 20-40°) and
• be coated at least with the TiAlN coating.

Steps for Drilling and Tapping Stainless Steel

Drilling and tapping stainless steel is easy when you use the proper technique.You can follow the following steps:

Drilling Stainless Steel

1. Determine the exact location of the hole in the stainless steel.
2. Choose the right size of drill bit for stainless steel, make sure it's smaller than the actual hole because you'll still be tapping it; use this table to help you choose the proper size.
3. Align the stainless steel and clamp it in place.
4. For stainless steel, a pilot hole can be made using a smaller drill bit.
5. Place a lubricant to prevent the stainless steel from overheating.
6. Drill at a slower speed and apply slight downward pressure; drilling too quickly and harder will generate too much heat, hardening the stainless steel.
7. Drilling should be paused from time to time to enable the drill bit and stainless steel to cool.
8. Continue drilling until a complete hole has been made. 

Tapping Stainless Steel by Hand

You can use Taper, Plug, and Bottoming tap.

1. Insert the tap's end into the hole.
2. Keeping the tap as straight to the stainless steel's surface as possible.
3. Using slight downward pressure, slowly spin the tap clockwise.
4. The tap's teeth begin to cut through the metal. Don't worry if it's a little shaky; keep going down into the hole, and it will eventually stabilize.
5. Expect the tap to become fairly firm after a quarter turn, this is due to metal chips.
6. To remove the metal chips, reverse the tap direction for a quarter or even a half turn.
7. Place Lubricant to prevent overheating and help remove the metal chips.
8. Repeat the process until the taps are all the way through.

Application table

In the application table you will find all our Twist Drills, which you can drill stainless steel with. If you click on the images below, you will be taken directly to the product page where you can find detailed information on each of our twist drills.

If you need help finding the right type of drill bit for stainless steel, or simply want some advice on how you should drill or tap stainless steel, then feel free to reach out to us at Quality Tools UK. We have drill bits and tools for all types of projects and always enjoy offering advice.