Measuring and Marking out tools in Workshop

Measuring and Marking out tools in Workshop

Introduction

This training module is designed to give you a good appreciation on the various types of band tools commonly used for measurement, marking out, and metal removal. Emphasis is not placed on you to become a skilful fitter within such a short period of training, but rather to let you understand the uses of common hand tools and appreciate the importance of fitting work in the trade. Nevertheless, on completion of the training and through the hands-on practice given, you will acquire some of the basic skills and techniques involved with these hand processes.

To get the maximum benefit from the training, it is essential that you use every opportunity to consolidate what you observe and to interact between yourself and the staff member in charge of your training. This is self-motivated and the drive must come from you.

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2. Why Use Hand Tools?

"Man without Tools is nothing; with tools he is all." - This sentence is defined by Thomas Carlyle has well elaborated the importance of tooling to a man.

The term 'Tooling' as applied to the engineering discipline refers to any equipment or instruments that give helps in the production of a product or any related activities. Simply speaking, it ranges from the most fundamental type of hand tools such as a File to the very complex machine tools such as a CNC Machining Centre.

Thus, one may ask the question - Why we still have to use band tools in this modern age of technologies?

Yes, it is reasonable to say that the efficiency of any hand processes is low and the outcome quality depends highly upon the skill of individuals. Perhaps it is fair to consider the following points before a definite answer is given to the above question: -

1. Accuracy

Although the CNC machine can give a higher degree of dimensional accuracy when compared with the inconsistent outcome of hand fitting, the extreme high degree of flatness required for a surface table or a machine slideway is usually obtained by hand scraping only.

2. Flexibility

Hand processes are very flexible and can be carried out at any place where necessary while machining processes are not. In addition, machining usually require a rigid setting up, while fitting is simple.

3. Quantity

For large batch size, advanced production machines are commonly employed in order to maintain the accuracy as well as the efficiency. But for "jobbing type" works, such as the manufacture of a prototype or the repairing of a single component, it would be uneconomic to use these advanced machine tools. Instead, "jobbing type" works are usually produced by conventional machining and followed by hand fitting where necessary.

4. Final Assembly

In the assembly of precise component parts, no matter how accurate they are being produced, a skilled fitter is often required to give the necessary "finishing touch" on them to ensure that everything goes together correctly.

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3. Measuring Tools in Workshop

3a. Calipers Calipers are the very simple tools used together with a steel rule for the measurement or comparison of linear dimensions. An experienced worker can achieve +/-0.05mm in the measurement. Calipers are classified into two types: - Outside Calipers Outside calipers (figure 1) are used for measuring external dimensions such as the length, diameter, or even the thickness of a solid. Inside Calipers Inside calipers (figure 2) are used for measuring internal dimensions such as the diameter of a hole, or the width of a slot etc.

Figure 1. Outside Calipers Figure 2. Inside Calipers

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3b. Vernier Calipers Vernier Calipers (figure 3) are more precise tools capable for measuring external dimensions, internal dimensions, and depths. Besides the two pairs of measuring jaws and the depth gauge, its main features also include a main scale and a vernier scale.

Figure 3. Vernier Calipers

The resolution of a vernier scale is determined by the difference on the distance of one division on the main scale and one division on the vernier as shown in figure 4. For example: A vernier scale of length 49mm is divided into 50 equal divisions. That means ONE division on the vernier represents 49/50=0.98 mm while ONE division on the main scale represents 1mm. Then, the resolution of the vernier is 1mm - 0.98mm = 0.02mm.

Figure 4. Vernier Reading

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3c. Vernier Height Gauge A vernier height gauge (figure 5) is used for measuring height of an object or for marking lines onto an object of given distance from a datum base.

Figure 5. Vernier Height Gauge

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3d. Micrometer

A micrometer is a more precise measuring instrument than the vernier calipers. The accuracy is come from the fine thread on the screw spindle. The ratchet prevents excess force from being applied. Generally, the screw spindle has a pitch of 0.5mm. The thimble is divided into 50 equal divisions.

Common types of micrometers used in the workshops are: -

Outside Micrometer An outside micrometer (figure 6) is used for measuring external dimensions. The work to be measured is placed between the anvil and the tip of the spindle.	Figure 6. Outside Micrometer
Inside Micrometer This is similar in structure to an outside micrometer and is used for measuring internal dimensions as shown in figure 7.	Figure 7. Inside Micrometer
Depth Micrometer A depth micrometer (figure 8) is used for measuring the depth of a hole, slot and keyway etc. A complete set of depth micrometer is equipped with spindles of different lengths, which can be interchanged to suit different measuring ranges.	Figure 8. Depth Micrometer

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3e. ProtractorEngineer's Protractor Engineer's protractor (figure 9) is a general purpose tool used for the measuring / checking of angles e.g. the angle of drill head, angle of cutting tool, and even for the marking out of angles on a component part.	Figure 9. Engineer's Protractor
Vernier Protractor This is a precision measuring tool that the accuracy of measurement can reach ¡Ó5 minutes of an angle through the vernier scale as shown in figure 10.	Figure 10. Vernier Protractor

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3f. Combination Set

Combination set (figure 11) is a set of equipment combining the functions of protractor, engineer square, steel rule, Centre finder, level rule, and scriber.

Figure 11. Combination Set

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3g. Dial Indicator The principle of dial indicator (dial gauge) is that the linear mechanical movement of the stylus is magnified and transferred to the rotation of pointer as shown in figure 12. The accuracy of dial indicator can be up to 0.001mm. It is usually used for calibration of machine.

Figure 12. Dial Indicator

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4. Marking Out Tools in Workshop

Marking out is the preliminary work of providing guidance lines and centres before cutting and machining. The lines are in 3-D and full-scale. The workpiece can then be cut or machined to the required shapes and sizes. The common tools used for marking out are as follow:

4a. Scriber A scriber (figure 13) is used for scratching lines onto the workpiece. It is made of hardened tool steel.

Figure 13. Scriber

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4b. Engineer's SquareEngineer's square (figure 14) is made of hardened tool steel. It is used for checking the straightness and the squareness of a workpiece. It can also be used for marking perpendicular lines onto a workpiece.

Figure 14. Engineer's Square

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4c. Spring DividersSpring dividers (figure 15) are made of hardened tool steel. The legs are used for scribing arcs or circles onto a workpiece.

Figure 15. Spring Dividers

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4d. Punch There are two types of punch namely the Centre Punch and the Dot Punch. A dot punch has a point angle of 60¢X and it is used for making of small dots on the reference line. The centre punch has a point angle of 90¢X as shown in figure 16 and it is used for making a large indent on a workpiece for drilling. Both punches are made of hardened tool steel.

Figure 16. Punch

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4e. Surface Plate Surface plate (figure 17) is made of malleable cast iron. It has been machined and scraped to a high degree of flatness. The flat surface is being used as a datum surface for marking out and for measuring purposes. If it can stand on the floor, it is called surface table.

Figure 17. Surface Plate

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4f. Angle Plate An angle plate (figure 18) are used for supporting or setting up work vertically, and are provided with holes and slots through which securing bolts can be located. It is made of cast iron and ground to a high degree of accuracy.

Figure 18. Angle Plate

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4g. Vee Block Vee blocks (figure 19) usually in a couple are made of cast iron or steel in case-hardening. They are generally used for holding circular workpiece for marking out or machining.

Figure 19. Vee Block