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Bench Work and Fitting

The bench work and fitting play an important role in every engineering workshop to complete and finish the job to the desired accuracy. The work carried out by hand at the bench is called bench work, whereas fitting is the assembling of parts together by filing, chipping, sawing, scraping, tapping etc., necessary after the machine operation. The various tools used in fitting practice are as follows:

1. Holding tools:

The holding tools or vices are required to hold the work firmly. The various types of vices for different purposes are bench vice, hand vice, pipe vice, leg vice and pin vice.

2. Striking tools:

The striking tools or hammers are used to strike the job or tool. The various types of hammers in common use are ball-peen hammer, cross-peen hammer, straight-peen hammer, double-faced hammer, and soft hammer.

3. Cutting tools:

The chief cutting tools used in fitting are cold chisels, hacksaws and files. These tools are discussed, in brief, as follows:

(a) Cold chisels. These are used to cut the cold metal and are made by forging from cast tool steel of octagonal cross-section. The cutting edge is ground to an angle suited to the material being worked upon. After forging to shape and roughly grinding, the cutting edge should be hardened and tempered. The most commonly used cutting angle is 60°, but this varies according to the type of material cut. The various types of chisels commonly used for fitting are flat chisel, cross-cut chisel or cape chisel, half-round chisel, diamond pointed chisel and side chisel.

(b) Hacksaws. The hacksaw is the chief tool used by the fitter for cutting rods, bars, and pipes into desired lengths. The cutting blades of hacksaw are made of carbon or high-speed steel. The blades are specified by its length and the point or pitch. The length of the blade is the distance between the outside edges of the holes which fit over the pins. The point or pitch is measured by the number of teeth per 25 mm length. The points of the teeth are bent to cut a wide groove and prevents the body of the blade from rubbing or jamming in the saw cut. This bending of the teeth to the sides is called the setting of the teeth. Usually, alternate teeth are set to right and left, every third or fifth tooth left straight to break up the chips and help the teeth to clear themselves.

(c) Files. A file is a hardened piece of high-grade steel with slanting rows of teeth. It is used to cut, smooth or fit metal parts. The size of the file is indicated by its length. It may be noted that coarseness or pitch of the file varies directly as the length of the file. Thus, larger the length of the file, coarser will be the pitch and smaller the file, finer will be the pitch.

4. Marking, Measuring and Testing tools:

The various marking, measuring and testing tools are Engineer's steel rule, outside and inside calipers, divider, surface plate, scriber, universal surface gauge, punch, V-block, angle plate, try square, combination set etc.

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