What is a spiral tap, how many types and how to choose?

What is a spiral tap?

Spiral tap (Tapping) or tap is a device used for creating threads to the workpiece with the tapping process. By cutting the internal thread inside the hole of the workpiece. which is classified in the group of cutting tools made of steel Or carbide is also used to process various metals. Creating a thread in the workpiece can be done by either manual threading. and machine tapping The threads produced by tapping have both internal threads and external threads.

Forms and methods for selecting spiral taps

1. Straight Flute Tap

This type of spiral tap widely used And is a standard way to create a thread for the workpiece. The characteristics of this type of spiral tap have two sides. The long side is used to drill through holes. The short side is used to drill blind holes. The disadvantage of this section is that there will be chips stuck in the thread groove. Causing the need to blow out the dust. This thread tap is made of high-strength materials such as high-speed steel. and cemented carbide This type of tap can often be seen in small-scale production.

2. Spiral Flute Tap

This type of spiral tap is designed so that between each cutting thread there is a chip discharge groove. So that in the process of tapping, the scrap material will be pushed back out along the groove. Helps prolong its service life. In addition, spiral taps have different angles to suit the rotational speed in the application. which will be divided into Low speed helix angle is 18-30 degree and high speed helix angle is 45-52 degree. Each angle is suitable for different materials such as

  • The helix angle is 45 degrees or more: suitable for malleable materials such as aluminum or copper.
  • Helix angle at 25-35 degrees : suitable for metal alloys that are fragile
  • Helical angle of 05-20 degrees : Suitable for very hard or very tough materials such as some stainless steels, titanium or nickel alloys.

3. Spiral Point Tap

This type of tap is similar to a straight fluted spiral tap. But there is a specialty that the tip of the flower has a groove that helps to push the material forward so that the chip does not get stuck in the tapping hole. Suitable for through-hole threading or applications that require high tapping speeds.

4. Hand Tap

It is a commonly used spiral tap. Suitable for manual or manual threading, made of carbon alloy steel. or high speed steel Very hard, suitable for threading hard materials. There are 3 types together:

  • Taper Tap : For use in thread cutting in very hard materials such as alloy and workpieces that require small threads with a high probability of breaking.
  • Taper (Plug Tap): The appearance of a spiral tap is similar to a taper (Taper Tap), but the length of the taper is less. Suitable for work with through holes or cut holes.
  • The last one (Bottoming Tap): The characteristic of this spiral tap is that it only has a slightly tapered end. To help enter the workpiece only at the beginning of the threading process. Suitable for pre-tapped holes of other pilot types. Used to create through and non through holes.

5. Forming Tap

This type of spiral tap Is designed to be different from other types, is to create a thread by rolling. or extruded the material inside the hole. In the working process of this type of tap, no chips are generated. because the chips will be compressed into the workpiece Suitable for creating threads for materials that are not very hard. therefore suitable for materials such as low carbon steel or aluminum

Tap size

There may be errors in the workpiece preparation by tapping. If the hole is too large, the resulting thread may have shallow threads. As a result, the resulting thread is not strong. or if too small More torque will be required. for threading which may cause the threaded tap to break Which will find the size of each type of threaded hole, both can see from the table of the product catalog itself or calculated using the following formula

Calculation of drilled holes for metric threads

Tapping hole size = outer diameter of thread – pitch

Calculation of drilled holes for American thread (Unified National Coarse (UNC))

Tapping hole size = outer diameter of thread – pitch where pitch = (1/number of threads per inch).

Calculation of bore holes for British Standard Whitworth (BSW) threads.

Size of the tapping hole = outer diameter of the thread – (2 x thread depth) + (allowance), the tolerance can be obtained as 2 x ¼ x thread depth.