What Size Drill Bit For Tap

 A tap drill bit is a kind of drill attachment that does tapping – a metalworking technique for creating threads in the holes. When you tap, you create threaded holes where you can screw in threaded bolts.

A tap drill is one of many types of drill bits. It is designed to create a hole of a specific size by cutting threads on the inside surface of the hole.

The difference between a tap drill and other drills is that the tap drill is not designed to cut through the workpiece completely.

Uses of a Tap Drill Bit

Tap drill bits are specifically used for creating threaded holes in metal surfaces. These attachments are used to create threaded holes to better secure screws of heavy-duty machines.

You can also use these drill bits when you need to repair or rethread a damaged fixing. Creating threads inside the holes is recommended for machines to have a more solid assembly, which you can do with tap drill bits.

Using tap drill bits is the best way to ensure the machines are safely threaded to metal surfaces.

Everything You Need To Know About Drilling And Tapping Holes

We’ve all given that small, non-load-bearing bolt just “one last turn,” which results in hours of regret and a mess of stripped-out threads.

Well, fear not, we have just the video for you. If you want a quick three-step video on drilling and tapping holes, this ain’t it.

In this video, Davin covers everything you need to know when drilling and tapping holes: essential tools, thread types, thread design, thread tolerances, and yes, the step-by-step process of drilling and tapping.

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Contents of this video:

  • 0:00 Intro
  • 0:12 Recommended tools
  • 1:33 Design of a bolt
  • 4:29 How to use the tools
  • 6:40 Determining thread size
  • 7:55 Reading a tap and die chart
  • 9:22 What drill bit do you need
  • 10:33 Drilling the hole (hand tools)
  • 12:18 Prepping the hole
  • 12:40 How a tap works
  • 13:07 Tapping the hole
  • 15:50 Finished product
  • 16:04 Tapping on a drill press
  • 20:15 Minimal tools needed
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Finding the Right Drill Sizes for Tapping

Tapping holes with the wrong size drill is a common mistake of machinists. This is usually because the size charts that some machinists use are outdated; these charts use high-speed drills as the basis when they were still the norm back in the 1950s.

One of the main reasons you cannot use outdated charts anymore is that many design engineers use high percentage thread values in tapped holes. They do this to reduce the chances of experiencing thread failure.

Another reason for the outdated charts is that drills used for tapped holes were commonly high-speed cobalt or steel back in the old days.

Today, tap drill holes are created with advanced carbide drills that can drill more accurate holes than the old high-speed drills.

Right Drill Sizes for Tapping

To know the correct tap drill size, always ensure that your tap drill size chart is updated. The correct tap drill size can have a major effect on the machining operation.

For pre-drilling applications, tool manufacturers suggest choosing values of thread percentages between 60 to 70.

The more strength you put in threading does not necessarily mean an increase in the percent of thread.

A rule of the thumb is: the tap life decreases when more thread strength is applied. Aside from the right drill diameter, the correct drill bit shape can also affect the efficiency of using these tap drill bits.

Selecting a Drill Bit based on Shape

When you enter a common hardware store, you’d see a wide selection of drill bits with different shapes and sizes.

There is a one-size-fits-all drill with a twisted shaft and a 118-degree point angle that you can drill into almost all household materials.

However, it is still important that a universal fit may not be the best choice at all times. In most cases, the right drill bit shape can also help in the success of tap drill bits.

1. Twist

Twisted drill bits have spiral grooves on their pointed tips to remove the hulls out of the holes. Twisted-shaped drill bits are most efficient in drilling steel.

Drill bits can also become dull over time the more frequently you use them. When they become dull, you can use a drill bit sharpener.

2. Auger

If you need to drill large holes to wooden surfaces, the auger is the shape of choice for the drill bits.

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Auger drill bits are also used in drilling soft materials, and they can easily drill medium to large-sized deep holes.

For efficient drilling, auger drill bits prefer low speed but with high torque.

3. Flat, Paddle, or Spade

These types of drill bits have flat bottoms with sharp tips positioned at the center. A spade drill bit keeps the surface on target better than other drill bit shapes, and you can use this when drilling on wood.

4. Forstner

A Forstner drill bit is one of the most efficient drill bits because it can cut two ways simultaneously. However, it would require more pressure to make the drill.

Forstner drill bits are of choice for modern kitchen units, wood, and softer materials.

5. Step

Stair-stepped drill bits are preferred when different holes have to be drilled all at once because of their design. This is the drill bit of choice for drilling sheet metal.

How to Use a Tap

Tapping a hole is easy with the right drill bit sizes and steps. Before using one, make sure that you are familiar with the step-by-procedure of using a tap.

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Drilling the Hole

  1. The most important step is to choose the right tap and drill set that you need. There are a variety of tap and drill sets with different indications that you can select online or in any hardware store.
  2. Secure the metal in place with a C-clamp or a vise. Keeping it steady prevents the metal from slipping while you are drilling, thereby also preventing any injuries.
  3. With the center punch of the drill, make a divot on the surface. The divot serves as the grip that allows easier penetration.
  4. After making the divot, insert your chosen drill bit into the chuck. Make sure that the drill bit is tightened and is secured in place.
  5. Apply a drilling oil into the divot. Drilling oil is a lubricant that helps make drilling easier and prevents the drill bit from overheating by reducing friction.
  6. Press the end of the drill bit into the divot on the surface. Apply pressure while starting to drill slowly to allow the drill bit to penetrate the surface.
  7. When the drill bit penetrates the metal, apply medium speed with constant gentle pressure. Do not put too much pressure when drilling, as this can break your drill bit.
  8. While drilling, retract your drill bit every 1 inch of blowing out metal flakes. Metal flakes can contribute to adding more friction, thereby causing your drill bits to overheat.
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Hole Threading

  1. Insert the corresponding tap to the T-handle. A t-handle helps in tapping drilled holes to create threads.
  2. Apply drilling oil again inside the hole, which you will thread.
  3. Insert the tap inside the hole. Make sure that the tap is aligned straight down so that the threads will be accurate.
  4. It isn’t easy to rethread, so you have to ensure that your tap alignment is accurate or when needed.
  5. With constant gentle pressure, rotate the t-handle clockwise repeatedly to start threading. When too much pressure is applied, you end up creating uneven threads.
  6. Once done, rotate the t-handle counterclockwise to remove the tap from the hole. Rotate it repeatedly to remove the tap entirely from the hole.

Securing a Drill Bit

When you have already chosen the right drill bit size, it is also important that you secure them properly in the chuck. Securing them prevents any accidents that may happen when you use them.

Whether you have a keyed or keyless chuck, there is a good process to change and secure drill bits to the drills.

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Keyless Drill

  1. Loosen the chuck by rotating it in a counterclockwise direction. This will open up the jaws that are clamping on the drill bit.
  2. Remove the bit. If the chuck is completely loose, removing the drill bit should be smooth and easy.
  3. Choose the bit that you will insert. Make sure that it is positioned so that its shank will directly insert into the drill’s chuck.
  4. Squeeze the trigger of the drill a few times while the drill bit is inserted. This tightens the drill bit in place.
  5. For drills with a ratcheting mechanism, engage by twisting it firmly in a clockwise direction to click and secure it in place.

Keyed Drill

  1. For drills with a chuck key, this is used to loosen the bit drills. Insert the chuck key by interesting its tooth to the matching hole on the outside surface of the chuck.
  2. Turn the chuck key counterclockwise to loosen the jaws that hold the drill bit in place. Continue doing this until you can feel that the drill bit can slide out of the chuck smoothly.
  3. Remove the drill bit and then insert the new drill bit you’d like to use.
  4. Using the chuck key, turn it clockwise to secure the new drill bit in place.
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How to Take Care of your Drill Bits

Regardless of the brand and how frequently you use your drill bits, a major factor in keeping them in good condition and working well depends on how you use and take care of them. Here are helpful tips for taking care of your drill bits.

  1. Drill with just the right speed. If possible, drill slowly.
  2. Do not drill a hole continuously. Always take time to remove the drill from time to time to remove metal flakes.
  3. Metal flakes can add to the friction and cause overheating of your drill. So make sure to check for metal residues when drilling.
  4. Always use drilling oil. The oil will serve as a lubricant to drill more efficiently; it helps prevent your drill bits from overheating and getting dull easily.
  5. Always secure the metal you are drilling with a clamp. This will prevent any injuries from happening and keep the metal in place as you drill.
  6. Always use the right drill bit for the material. If you don’t, you might end up damaging the material instead of creating a hole.


How do you select the correct tapping drill?

The right tapping drill size ensures that proper even threads are created in the holes. The rule of thumb is to subtract the pitch from the thread diameter for the metric scale and then choose the next larger drill size.

You can apply the same rule to imperial threads.

What is the strongest drill bit?

Drill bits are made with different materials. The material of choice usually depends on the surface you will be drilling.

You can buy drill bits in sets ranging from various sizes so that you will have the liberty to try each size out to see which drill bit will fit the best.

Generally, the strongest drill bit is the one made with carbide material. Carbide drill bits are only used with professional work coupled with heavy-duty and high-end tools and equipment.

Carbide is brittle, which is why it’s contraindicated for hand drills and drill presses.

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What is a tap and die set?

A tap and die set is mainly used to screw threads. The tap forms the nut, while the die forms the male the bolt.

The tapping process is called tapping, while the due process is the threading part. When a tap and die set is used to clean threads, the process is called chasing.

What is the Best Drill Bit Set?

Frankly, there is no best drill bit set because the chosen drill bit set will depend on your work material.

With this, you should be familiar with the types of drill bit sets available and what material they’re most compatible with.

Do all drill bits fit?

Most drills today are flexible and are compatible with many types of drill bits of different materials and lengths as long as the bit’s shank fits the chuck perfectly.

Brands do not always matter, as there are some brands that you can also use in drills from another manufacturer.

With this in mind, do not forget that not all drill bit designs are compatible with all tasks. There are still drill bit materials preferred to carry out particular jobs for efficiency.

Final Say

Tap drill bits are your companion with screwing threads for your metalwork. You must know how to properly secure them to your drills and choose the right drill bit size to create even threads in the holes.

Also, make sure that you follow the tips presented above for using a drill with tap drill bits to prevent any injuries and maintain your drill bits in good condition!

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