How to tap left hand threads

Changing Thread Direction on a Nut- Left Hand Thread- Makeshift Cutter. TIG Welding


The die is a nut with internal slots and external locks for turning the tool. It can be of various shapes. round, square or hexagonal. If the work is carried out at home, you will need a vice to fix the part.

Reverse thread tap

Before doing the work, the main thing is to choose the right diameter of the workpiece. It should be 0.2-0.3 mm smaller than the size of the future thread. For metric, you can use the data from the table.

The workpiece must be prepared in advance. If its section is not a circle, you need to turn it. Then a tapered chamfer is removed on the end part to mark the first thread.

Next, you need to follow exactly the instructions:

  • Having fastened the workpiece in a vice, the correctness of its location is checked.
  • Installing the die into the die holder. Its surface should be in the same plane with the surface of the end face of the workpiece.
  • The first turn is done with little effort. It is important to make turns in the right direction.
  • Having reached the bottom border. the die must be rotated in the opposite direction.

One such pass will not be enough to form a thread with good geometry. It is recommended to repeat the procedure 3-4 times until the die is free to twist onto the workpiece. To check the quality, a nut of the appropriate diameter should be tightened. If force is observed, you can process the outer part of the workpiece with fine-grain emery paper.


To form internal threads, taps must be used. They represent a cylinder with an external groove. If it is necessary to process small parts with a diameter of up to 20 mm, you can use the manual type of tap. Large dimensions require machining using a machine.

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It is best to use a complete set of taps. It includes three parts for roughing, intermediate and final shaping of threaded holes. If there is a drill in the home kit, it is recommended to purchase taps with a tail mount.

Ep 55: Tapping Left Hand Threads

The workpiece must be secured. If this is a large-sized part, this can be done using clamps. For small products, a vice is used. Having secured the part, its position relative to the tap is checked. The axis of the latter must be strictly perpendicular to the plane of the workpiece. The first pass will be done with great effort. Remember to use a coarse tap for this. Having formed the primary thread, a tap is used for the intermediate one. And only after it you can proceed to the final processing.

A little about the features of the tool

At the first stage, you should decide on the type of thread. It is divided into 2 main types: metric and imperial. The first one with the left direction is most often used. In order not to measure the distance between the grooves, you can recognize the type by the shape. A metric thread in cross section is an equilateral triangle, and an inch is an isosceles.

What products use a particular thread type? Fasteners use metric and plumbing uses inch. In addition, the following factors must be taken into account that affect the cutting process of connecting elements.

  • If the thread is intended to be connected to an already finished part, its geometric dimensions must be appropriate.
  • In the manufacture of fasteners completely. it is recommended to use the metric type.
  • The diameter of the workpiece must be different from the thread size. For the outside. downward, for the inside. upward.

Self-cutting of threaded connections is performed using dies and taps. They are made of high-strength steel with a standardized size of the working fluid.

How to cut a thread correctly. Mecca of the instrument

You can talk for a very long time about how to cut the thread correctly. Whole books and monographs are devoted to this. But, the overwhelming majority of the threads used do not require special skills when cutting, and we will stop our attention on the main methods.

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Internal threading

To cut internal threads, taps are used. tools like a screw with cutting grooves. Typically, two taps are required for the black cut and the finish cut. The difference is in the grooving depth. There are also three-pass taps and other cutting options. To work with them, special wrenches are required, which may be different in design, but must necessarily be suitable in size for the working tool.

It is very important to prepare the hole with the correct diameter before threading. Otherwise, you will either break the tap (if the hole diameter is less than required), or you will get a poor-quality thread. So, if an internal thread M10 is required, i.e. 10 mm in the groove diameter, then the hole diameter should be 8.5 mm. This is determined based on the thread pitch. For M10, it is 1.5 mm and, accordingly, the required hole diameter will be 10-1.5 = 8.5 mm. The steps of the threads can be found using special formulas, although the simpler option will not be to calculate the diameter, but to find out its value from the table.

left, hand, threads

After preparing the hole, we proceed directly to considering the issue of how to properly cut the thread. We attach the tap to the holder and start slowly screwing it into the hole, paying special attention to the accuracy of the direction. Slicing is performed clockwise with the application of certain efforts.

For successful cutting, the tap must be sharp and of good quality. The duration of its operation and the likelihood of breakdown depend on the use of the lubricant. A few drops of oil will not only make cutting easier, but also improve the quality of the threads. This is especially important for cutting blind holes. Naturally, it doesn’t hurt to have certain skills that come with practice. However, this operation is relatively simple and skills are acquired after 3-4 threads.

Tapping. how to tap threads by hand?

How to cut a thread with a threading device was described earlier. The threading device differs greatly from the tap device, but the principle of threading with both tools remains the same.

left, hand, threads

A tap is a metalwork and turning tool, in its shape somewhat reminiscent of a long rod. Inside this very rod, there are cutting elements, with the help of which the threads are manually cut.

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The tap can be used for more than just cutting new threads. With this tool, you can also restore the thread, making it as “new”.

By the principle of work, taps are manual and machine. Machine taps are fixed to the lathe and the threads are cut automatically.

Features of the applied technology

You can do the work in question with your own hands in a domestic environment. To do this, you need to take into account the recommendations below:

  • Before creating the hole, it is recommended to make a small indentation to ensure correct drill entry. For this, you can use a core. When drilling for metal, it is recommended to set the drill at low speed, which will achieve high quality processing. Before starting drilling, you can process the cutting edge with a special compound, due to which the tool will more easily enter the metal.
  • At the time of creating the hole, the drill with the drill should be located strictly perpendicular to the surface to be treated. At the time of using the tap, the cutting edge should be constantly lubricated with engine oil, and also make sure that the tool is located strictly parallel to the axis of the hole created.
  • In almost all cases, chamfering is carried out at the entrance of the hole, the size of which is 0.5-1 mm. To do this, you can use a countersink or a larger diameter drill.

It is not recommended to apply a heavy load to the handle by using a lever or gas wrench. Do not forget that the tap may burst due to high load, then remove the remaining

If you need to manually cut external threads for a pipe connection, make a stud or a bolt for a nut with a metric thread, a simple but rather effective tool is most often used. a die. The thread preparation process is quite simple if you follow the instructions below exactly.