All about blind hole taps

Lovers of technical work of various types and those who are professionally engaged in them need to know everything about taps for blind holes and how they differ from through taps. Taps M3 and M4, M6 and other sizes deserve attention.

All taps, regardless of type, belong to the category of metal-cutting devices. They solve 2 main tasks: applying a thread from scratch, or calibrating an existing thread. The processing method may differ according to the size and other parameters of the workpieces. Visually, such a product looks more like a screw or a cylindrical roller. The largest thread diameter, regardless of the type of holes, 5 cm.

Machine taps for blind holes, and this is their main difference from through holes, have a different shape. When punching a through hole with grooves, straight flute models are usually used. If the tap has a spiral flute, then it is usually intended for a blind recess. But some spiral products, with the left direction of the spirals, can also be useful for through marking, which makes it easier to dump chips. All hand tools are made with a straight flute, and are not subdivided into blind and through.

The reliability and practicality of threaded connections motivated engineers to actively develop tools for them. Differences can be in structural material, in the type of grooves. To avoid confusion and problems, a special GOST was developed at a certain point. The requirements of GOST 3266-81 apply equally to manual and machine modifications.

Products of 1, 2 or 3 groups are of the metric type. A, B (with numeric indices after Latin letters) - designate pipe models. If the tap is designated as C or D, then it is an inch tool. Well, the 4th category refers exclusively to manual devices.

The dimensions are shown in the following table:

The manual tap type is optimized for operation without the use of special equipment. Mostly it is supplied in the form of kits. Each set contains roughing tools for preliminary work. In addition to them, medium tools are added that increase the accuracy of the turns, and finishing (designed for debugging and calibration). Machine type taps are used only after installation inside the machines; in combination with the special geometry, this allows you to significantly increase the pace of work.

Lathe taps are machine tools. Their very name speaks of their use in conjunction with lathes. There are also machine-manual options. When working by hand, they can have a thread pitch of up to 3 mm. Such a device is almost universal.

It is very important to ensure the exact position of the drill in a specific location. For this, a depression is formed at a preselected point. It is created using a core and a simple hammer. The drill is fixed in the chuck of a drill or other boring apparatus with a low speed setting.

The tap must be lubricated regularly. It is very important to ensure that there are no distortions, and that the movement goes exclusively in the given direction.At the entrance to the hole, a chamfer is removed to a depth of 0.5-1 mm. Chamfering is performed either with large-section drills or countersinks. The tap is oriented in relation to the part and the hole immediately, because after insertion into the hole, this will no longer work.

Two turns of the tap are carried out in the course of cutting. The next turn is done against the move. This way, the chips can be dumped and the load can be reduced. Sometimes the question arises, how to get a broken tap. If it comes out partially out, just clamp it with pliers and turn it inside out.

It is more difficult to extract a piece that is completely in the hole. You can solve the problem by:

• pushing hard wire into the tap groove;

• welding the handle;

• the use of mandrels;

• Welding on a square-tipped shank (helps with particularly strong jamming);

• drilling with a carbide drill at a speed of up to 3000 rpm;

• electroerosive burning (allowing to save the thread);

• etching with nitric acid.