HowTo: Mechanics – Cut internal thread

Whenever possible I try to use finished nuts or thread inserts when using screws and the like. But sometimes there is simply no other way and you have to cut a thread into a material yourself. 🙂

That sounds a bit complicated at first but is really not difficult. Here comes a small series of pictures of how you can proceed when cutting a thread.

Hints for our lovely english readers: Basically, many of the articles on are translations from the original german articles. Therefore, it may happen here and there that some illustrations are not available in english and that some translations are weird/strange/full of mistakes or generally totaly wrong. So if you find some obvious (or also not obvious) mistakes don't hesitate to leave us a hint about that in the comment section. 
Also please don't get confused, that instead of a "dot" often a "comma" is used as decimal separator. 🙂


Tools required:

In the following list you will find all the tools you need to implement this article.

Safety instructions

I know the following hints are always a bit annoying and seem unnecessary. But unfortunately, many people who knew it "better" from carelessness lost their eyes, fingers or other things or hurt themselves. In comparison, a loss of data is almost not worth mentioning, but even these can be really annoying. Therefore, please take five minutes to read the safety instructions. Even the coolest project is worth no injury or other annoyance.

Affiliate links / advertising links

The links to online shops listed here are so-called affiliate links. If you click on such an affiliate link and shop via this link, receives a commission from the online shop or provider concerned. The price doesn't change for you. If you do your purchases via these links, you will support in being able to offer further useful projects in the future. 🙂

Assemble the thread cutter

There are different types of thread cutters.

However, the “traditional” thread cutting set consists of the four parts shown.

Next to the handle on the left …

… the three thread cutters are the most important parts.

These consist of:

  • Pre-cutter: marked with one circumferential ring
  • Middle cutter: marked with two circumferential rings
  • Finishing cutter: without ring

The individual thread cutters can be inserted into the holder and clamped as shown.

The tap used should be firmly clamped in the holder.

Place the tap

Here you can see the housing that is used in the article ESPEasy – level sensor with VL53L0X / VL53L1X. A cable gland must be screwed into this. To do this, there must of course be a thread in the housing. Perfect reason to test our tap. 🙂

To do this, position the pre-cutter – i.e. the tap with one ring – as straight as possible. It should be from above and …

…from the side as vertical as possible.

You have to be careful with the first turns because you need a little more force until the tap has “grppied” in the mterial.

As soon as you have the first threads in the material, you can carefully continue turning.

The following is important:
A span is created during cutting, because material is cut from the housing. So that it does not become too large and possibly block your tap, you should breakt it.

This is relatively easy by turning the tap back half a turn after each full turn.

This is a bit tedious but you avoid using it to damage the tap or the thread itself. 🙂

If you have kept this up, you should have cut the complete thread after a while with the pre-cutter.

You are now at the end of the first tap.

You should now repeat the whole thing again with the center cutter and finally with the finish cutter.

Each tap cuts the threads a little deeper and more precisely. You should (can) screw in a corresponding screw only after the finished cutter can be easily rotated through the finished thread.

Test thread

After you have finished cutting the thread, it is now time to test the cut thread. 🙂

A suitable screw is best suited for this. In the case of the housing for the level sensor, this is the corresponding cable gland.

This should be able to be screwed into the thread without need of strong force. If you need a lot of force you may have forgot to cut the thread completely with the finish cutter?

If the correctly cut thread still does not fit, you may have. used a tap with the wrong pitch.

View of the screwed-in cable gland from the inside.

Have fun with the project

I hope everything worked as described. If not or you have any other questions or suggestions, please let me know in the comments. Also, ideas for new projects are always welcome. 🙂

P.S. Many of these projects - especially the hardware projects - cost a lot of time and money. Of course I do this because I enjoy it, but if you appreciate it that I share these information with you, I would be happy about a small donation to the coffee box. 🙂

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