From types, difference to calculation; know all about matric thread gauges here!

UNF thread plug gauge

Metric thread gauges are a significant tool that helps in creating appropriate thread angles to hold or join several things. Talking of engineering, thread taps and gauges play an irreplaceable part in this domain. With the help of taps, you can create perfect threads with an appropriate angle to attach the screw.

But, how will you know how long should the tap be? For this, you need to have sound equipment which will suffice the need of measuring length, breath, diameter, thread angles, etc. To do this, it is imperative to have an in-depth knowledge about gauges.

Let’s discuss some of it in the following sections.

What are the different types of metric thread gauges?

Here is a list below of the thread gauges which you need the most –

— UNF thread gauges
— UN
— Trapezoidal
— Whitworth
— UNC thread gauges

These are the few of them that you will need most. But, amongst all these, if you are into engineering, there are few things more to know that will make your process of measuring, creating threads and fixing things easier.

UN, UNC and UNF thread gauges — terminologies

When it comes to measuring unit, it is of extreme importance that you understand the basic difference otherwise working on it can be quite difficult. This is exactly what you are to learn here.

As per the definition in ANSI/ASME, UN series is the new introduction to replace the old N-series of taps and threads. UNC refers to Unified Coarse or National Coarse in retailing. Whereas, UNF refers to Unified Fine or National Fine in retailing.

What are the aspects you need to know for calculating metric thread gauges?

It is not like seeing the size and measuring with a scale. When performing any metric thread calculation, there are different logistics that you must keep in mind –

i. To calculate diameter

There are 5 measuring data that you need to check – major diameter; pitch diameter, minor diameter, over wires, wires diameter.
ii. To calculate thread builder

This calls for 4 data if the number of Starts is 1. Here are the data that you need to check – Basic diameter, thread per inch, designation and class. You can change the class per requirement. For example: In UNC, unlike UNF thread gauges, the basic class is 2A but for finer thread calculation to the setting can be changed to 1A class.

iii. To calculate V- shape

Calculating V shape is very simple only when you have the following data –

Pitch, real pitch, crest flat, crest radius max, root flat, root radius, thread depth and flank length.

iv. To calculate Tolerances

Tolerances are the measurement to calculate the strength. With this, engineers decide which screw is to place where (this is why a small door hinge screw is different from railway track screw). Things you must check are – Allowances, major diameter, pitch diameter, minor diameter and length of engagement.
v. To calculate Lead angle

This determines the slant angle of a screw. Keeping this in mind; here is what you need to know – major diameter, pitch diameter, and minor diameter.

If you want to get the best and most appropriate metric thread gauges for your work, then do not compromise with the quality. Always buy it from the authentic industrial place. Start your engineering creations now!

5 Questions about metric thread taps you always wanted to ask

Often it is seen that, people new to the world of taps and dies find it quite difficult to figure out the correct equipment required for specific threading purposes. Moreover when working with metric thread taps, a myriad of questions loom their minds in search for the right threading instrument. If you can relate to these dilemmas then the following questions to answer your problems in the most subtle way! So, read on.

1. Why does the size of a tap vary as compared to its internal thread design?

The process of cutting threads into a hole by inserting a rotating tap is known as tapping. This rotating tap is bored beforehand to the specific size. In most cases, the internal thread size becomes larger than its tap. A tap’s pitch diameter should be closer to its minimal range because of this tapping tendency. This should also be within the range of its thread size.
2. Why are tap ends of threads grounded off at a specific angle?

The primary motive is to avoid the cutting edges from getting chipped. This is protected by the inclined ground off threads at tap ends. For example, Trapezoidal thread taps have comparatively low tensile strength towards its edges.

If you start cutting threads using trapezoidal thread taps from beginning, it might cause damage to the cutting edges due to high load on the tap edge. These grounded off inclined mechanism cuts threads slowly decreasing the load of cutting considerably.
3. What is the necessity of flutes of tap?

Flutes serve as a space to accommodate chips. One cannot have a cutting edge if he uses a tap without a flute. One should maintain caution not to use flutes that are too small. This is because a tap might be damaged by chips packed in its flutes.
4. Specify the kind of materials used for metric thread taps?

Normal materials used for casting taps are light alloys, titanium alloys, iron or even plastic depending on the purpose. Other versatile tapping materials are also used which is purpose specific. These include vanadium, chromium, Molybdenum, Tungsten, Cobalt and some other dependable alloy steels.

5. Explain surface treatment?

Chromium clad was the primary material used for surface treatment. It is a process of extending a tool’s life by placing that hard layer over the tool surface. This kind of surface treatment has gained popularity over these years and is used in almost all cutting tools.

6. Why are no chips produced in thread forming taps?

When normal taps cut threads, chips are produced. But thread forming taps carve out threads by inserting themselves into its surface. Thus no chips are formed. They do not include cutting edges or flutes. In this case, relatively soft materials are used as the process involves inserting the thread forming tap into the surface of the material.

Therefore, to conclude:-

It can be seen that the choice of taps in very crucial in order to get that perfect thread. Moreover, taps which are not grounded off at a certain angle may cause the thread edges to break off. So, one needs to judge with care your choice of metric thread taps and make sure you select the correct apparatus.

Frank Xu is the author of this article on metric thread taps.
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