Last updated: August 11, 2021

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In order for the screw to be fastened, you also need the appropriate counter-thread. Threads can be used to join components together and, unlike welding, to separate them again. However, the screw does not always fit with the threaded hole. The thread could be rusted or damaged. The hole may not even be there. To solve the problem, a new thread must be cut. To be perfectly equipped for this, you need a thread-cutting set.

In our thread cutting set test 2021 we explain what you should look for when buying your set. To get an overview of the different types of thread cutting sets and to compare the advantages and disadvantages, we have put together some information for you in this article.




Summary

  • The thread cutting set is a set of utensils that enables the recutting and cutting of threads.
  • A distinction is made between two types of thread cutting sets. For the internal thread, the single-cut tap set and for the external thread, the cutting insert. The newer sets contain both types.
  • A very important purchase criterion for a thread cutting set is the size of the threads. These can be according to European, British or American standards.

The best Tap: Our Picks

Guide: Questions you should ask yourself before buying a thread cutting set

What is a thread cutting kit?

To explain what a thread cutting kit is, we first need to explain what a thread is.

A thread is a profiled indentation that runs continuously in a cylindrical inner or outer wall. Various thread forms have since been developed in response to cultural preferences.

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Tapping produces chips. These should not be removed during the cutting process, as it leads to cuts.
(Image source: Pixabay / Capri23auto)
Taps are used for internal threads and dies for external threads.

Tapping sets are therefore sets of utensils that are used to cut internal or external threads. To cut an internal thread, you need a tap. The tap simultaneously drills and cuts an indentation along the cylindrical inner wall.

To cut an external thread, you need a tap. This cuts an indentation along a cylindrical outer wall.

These special sets contain all the necessary thread cutting tools. This allows you to cut the thread yourself without any problem. Conveniently, most of these tool sets come in a case or box. This makes it very easy to transport and store the tools.

What is a tap set used for?

Taps are not only used for craftsmanship and industry, but also for private use. Whether for the repair of a rusted or defective thread, or to create a new screw connection in metal, the tap set is the best help.

With the thread cutting set it is possible to cut a thread in a large number of materials. Such as: Wood, plastic, aluminium or plastic. This makes the tap an all-rounder.

To make sure that you are properly equipped, you should think about the type of tap before buying. Do you want to cut an internal or external thread? Or do you need a set that contains both types? The thread form is also decisive for the choice of your thread cutting set.

For private use, a small thread cutting set is sufficient. However, if you use it as general workshop equipment, we recommend that you go for a high-quality universal thread cutting set. As they offer a variety of taps.

What alternatives are there to the tap set?

The tap set offers a very wide range of applications. As a result, it is considered a universal tool in all areas. Nevertheless, as an alternative to the tap, there are three different types of drill: combination tap, thread milling cutter and thread former.
Type Description
Combination tap Core hole drilling, tapping and deburring are combined with this one tool. Of course, you save a lot of time by carrying out the work steps with a single tool. However, you need a cordless screwdriver to use this drill.
Thread former with this tool the thread is created by forming and not by cutting. By pushing the material to the side through the edges of the tap, the shape of the grooves is taken after repeated turning. As the thread profile is pressed into the material, no chips are produced.
thread cutter in which the thread cutter rotates at a very high speed, the material is removed. The feed movement during milling is perpendicular to the tool's axis of rotation. This process, like tapping, produces chips.

Although the combination tap is a time saver, there are a few things you should be aware of. If the combination tap is not used properly, the thread can break quickly. It is important that only the cordless screwdriver with a torque limit is used, otherwise the drill can jam and cause serious hand injuries.

Thread forming or thread grooving is a chipless process. However, this drill cannot be used for all materials and it is impossible to resharpen it. To form a thread, a higher torque is necessary. This results in a much higher heat generation, in contrast to cutting.

The thread milling cutter also offers the possibility of drilling and threading in one step. It is possible to mill almost all materials with this tool. However, profile deviations occur with a small thread profile angle and coarse pitch.

Decision: What types of taps are there and which is the right one for me?

So for an internal thread you need a tap and for the external thread you need a die. A distinction is therefore made between two types of tap sets:

  • Single Cut Tap Set
  • Tap set

In the following point we have described a few advantages and disadvantages that each type of tap set has.

What distinguishes a single-cut tap set and what are its advantages and disadvantages?

The single tap set is responsible for cutting the internal thread. As the name suggests, it is possible to cut the internal thread with this tap in one operation.

Apart from the single-cut tap, the tap set is used for some materials. These sets usually contain taps that are needed for the three working steps: Pre-cutter, centre tap and finish tap. You can distinguish the taps by the rings on the shank. The roughing tap has one ring, the centre tap two and the finishing tap none or three.

However, to be able to cut the thread, you need a tap wrench in addition to the single-cut tap. The drill is clamped in the tap wrench. This gives you a stable holder that enables you to turn the tap into the core hole.

The set sizes are very different. Some contain 7 and others contain 15 parts, or even more. The smallest sets contain only three taps. They contain different tap sizes and types, as well as a tap wrench.

Advantages
  • Effective internal threading
  • low force, which reduces the risk of breakage
  • higher precision
  • at least three threads in the set
Disadvantages
  • It is not possible to cut an external thread
  • No die in the set

What are the characteristics of a die set and what are their advantages and disadvantages?

The die insert is responsible for cutting the external thread. Dies are round inserts that are fixed to a die holder with several retaining screws. Then, with the help of the notches inside the insert and the rotary movement, an indentation is cut into the cylindrical object. The chips are removed through the cavities between the cutting edges of the cutter.

Without the die holder it is not possible to use the die. It should be noted that depending on the size of the desired thread, the dies also have different sizes. These also require a suitable holder.

Advantages
  • Fast and effective external threading
  • Extensive sizes and shapes of dies
  • Can also cut harder steel
Disadvantages
  • It is not possible to cut an internal thread
  • Requires a die holder

The die sets usually contain 7 or 8 different dies with different sizes. The set also includes a die holder. However, it is not possible to cut an internal thread with these, as they do not contain a tap.

Buying criteria: You can compare and evaluate a thread cutting set on the basis of these factors

Thread types

Throughout history, people have created different types of threads because cultural preferences were very different. Today, we distinguish between different types of threads because we have specific requirements for strength.

The most important thread types are:

  1. ISO metric thread (M). This thread is standardised worldwide. It has an angle of 60 degrees and is defined by the German Institute for Standardisation in DIN 13 and DIN 14. The outer edges converge in a wedge shape, which prevents the thread from loosening by itself. The diameter and the pitch are given in millimetres. This is marked with an M.
  2. Metric ISO fine thread (MF). The only difference between this thread and the ISO thread is the pitch. The pitch is measured between two threads and indicates how far the thread moves into the substrate in one turn.
  3. Trapezoidal thread (Tr). The trapezoidal thread has the shape of a symmetrical trapezoid, which is how it got its name. This thread has a flank angle of 30 degrees. The sharp-edged trapezoidal thread is defined in DIN 380, the rounded trapezoidal thread in DIN 30295 and the metric ISO trapezoidal thread in DIN 103.
  4. Unified National Coarse Thread (UNC). The UNC is most commonly used in the USA and Canada. The unit of measurement is inches instead of centimetres. This thread is mainly used for computer components. The flank angle is 60 degrees.
  5. Unified National Fine Thread (UNF). This thread is the American fine thread. In Europe, it represents the ISO metric fine thread.
  6. British Wirtworth Thread. The Wirtworth thread originates from Great Britain and is mainly used for pipe connections. The angle is 55 degrees and the main unit of measurement is inches. In Germany, the thread is defined in DIN 11 and 12.
  7. British Standard Whitworth Coarse (BSW/WW). The angle is 55 degrees and BSW is measured in inches. This thread is equivalent to the ISO metric thread.
  8. British Standard Fine (BSF). BSF is the English version of the fine thread. It is measured in inches and has an angle of 55 degrees.
  9. British Standard Pipe (BSP). The BSP has the same characteristics as the Whitworth pipe thread. Because it is a cylindrical thread, it is not self-sealing.

Material of the tap

When buying a thread cutting set, you should also pay attention to the material of the tap.

Most taps are made from High Speed Steel. This high speed steel is called HS, HSS or HSSE steel abbreviation. These materials are very hard, wear-resistant, tempering and have a heat resistance of up to 600 degrees.

Tungsten steel taps are suitable for industrial areas such as construction or agriculture. Tungsten steel is a high-alloy steel, i.e. a stable material with a longer service life.

Trivia: Interesting facts about the topic of thread cutting sets

How do you cut a thread with a thread cutting kit?

Cutting internal threads

To cut the internal thread, in addition to the tap and the tap wrench, you will need: a centre punch, a bench drill, countersink and some lubricant.

  1. Mark the thread position. To make sure you drill in the right place, you should mark the thread position beforehand.
  2. Centre punch. In order not to deviate from the desired position, you should centre punch the material before drilling. To do this, place the centre punch in the marked position and tap it with the hammer.
  3. Pre-drill. After the material has been punched, the core hole for the thread is drilled. Make sure that the hole is the right size. Depending on the thread size, you can look up the appropriate diameter in the ISO thread tables.
  4. Countersink the hole. After drilling, you have to countersink the hole. This is done with a 90 degree countersink. Make sure that the countersink diameter is always 0.5 mm larger than the nominal diameter of the thread.
  5. Cut the thread. The last step is to cut the thread. For this you need a tap, a tap wrench and oil or grease. Before you start the tap, lubricate your core hole with some grease. After two turns, turn the tap back half a turn. This will break the chips and make the work easier.

Cutting the external thread

To cut the external thread, in addition to the die and the die holder, you will need: a bolt, a file and lubricant.

  1. Determine the diameter. To determine the thread size, first measure the diameter of the bolt. Depending on the size, a certain bolt diameter is needed. You can look this up in the ISO thread tables.
  2. File. File the round bar at a 45 degree angle to make it easier to cut the thread.
  3. Cut the thread. Insert the die into the die holder and tighten. You can see a small groove on the die, this must be inserted on the side with the three fixing screws, towards the middle screw. Put cutting oil on the round bar and turn the cutter clockwise. After one turn you have to turn the cutter back again to break the chips.

How big must the core hole be to drill the thread? Table

In order for the thread to be cut, the core hole must also fit the desired shape and size of the thread. A core hole that is too small can cause the tap to break because of the increased chip pressure. If the core hole is too large, you will not have any material left to cut the thread.

The following applies to calculating the core hole diameter:

Nominal thread diameter - thread pitch = core hole diameter

Example: core hole M10

10 mm - 1.50 mm = 8.5 mm (core hole diameter for M10)

In order to have a better overview of the core hole diameter and the pitch of the ISO thread, we have created a table for you. This table shows the core hole diameter for the metric ISO thread.

Thread size Core hole (mm) Regular thread Pitch (mm)
M1 0,75 0,25
M2 1,6 0,40
M2,5 2,1 0,45
M3 2,5 0,50
M3,5 2,9 0,60
M4 3,3 0,70
M5 4,2 0,80
M6 5,0 1,00
M7 6,0 1,00
M8 6,8 1,25
M9 7,8 1,25
M10 8,5 1,50
M12 10,2 1,75
M14 12,0 2,00
M16 14,0 2,00
M18 15,5 2,50
M20 17,5 2,50

Safety measures for thread cutting

Safety is the most important thing. To ensure your safety, you should take a few precautions when threading.

  1. Put on protective goggles. Although the tap and the die are made of a hard material, it can still break. The high tension can then cause eye injury.
  2. Do not remove the flow chips. Tapping produces sharp-edged flow chips, which can cause cuts. Do not remove these chips during the cutting process.
  3. Do not wear gloves. Gloves should not be used with rotating tools. There is a very high risk of the glove being grabbed and wrapped around the tool.

Image source: Mkphotography/ 123rf.com

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