Fitting bench Processes

MARKING

It is the first and important operation that is performed in bench working, since the accuracy of the product depends upon this. Before marking the surface to be marked is quoted by the chalk paste and allowed to dry. Then the job is kept either on the surface plate or on V block. The measurement is performed on the job by appropriate measuring instrument, then marking is done by scriber, surface gauge and identification is done by punches.

CHIPPING

Int his operation the material is removed in a stock by the help of chisel at room temperature. For large surface first the metal is removed by cross cut chisel and then remaining metal is chip off by other chisels while chapping lubrication is necessary for better life of chisels. For chipping three things are important  1st proper selection of chisel based on operation, 2nd proper grip of the chisel and appropriate position of standing by the operator. It is very accurate method of removing metal in a more quantity with a reasonable finish.

SAWING

It is an operation which is required to cut the metal in different shapes and sizes. It should be done slowly and standing position is appropriate for this operation. Cutting takes place in forward stroke of hacksaw and backward stroke is ideal. During operation full length of blade should be used. The best result is obtained if the hacksaw blade is fixed I proper direction with correct tension. Coolant must be used while cutting.

FILLING

It is an operation which is performed by the help of files. The pressure for cutting should be exerted in the forward stroke and backward is ideal. If the file is moved diagonally on the flat surface then it gives the best results. Initially a rough file is used to remove the rough metal followed by a smooth file for better finish. Filling is done by three ways first cross filling is for more metal removal then followed by straight filling and draw filling for final finish.

SCRAPING

This a manual operation done in a fitting shop for producing more accurate finish than obtained by filling. In this operation removal of metal takes place in small quantity at a localized portion. In this first a Prussian blue is applied on the surface in which higher spots will be noticed. By this operation the higher spots are removed till entire surface becomes perfectly smooth and uniform.

DRILLING

It is an operation done to produce holes either blind or through in a metal piece by the help of drills that are discussed earlier. It is done on the drilling machine in which first the job is held firmly on machine vice. Then the drill is fixed on the machine and it is lowered by the hand wheel. Appropriate coolant is used for cooling during operations.

TAPPING

It is an operation of cutting the interval threads by the help of tap and a tap holder manually.

DIEING

It is the process of cutting external threads by the help of die and die holder.

DRILLING MACHINES

BENCH DRILLING MACHINE

It is used for drilling, reaming, counter sinking, counter boring etc.

HAND DRILLING MACHINE

It is used for making very small holes. The spindle of this machine is rotated by a crank. It is pressed from the handle with left hand while crank is rotated with right hand.

PORTABLE DRILLING MACHINE

It is used for medium size holes. The machine is compact and is small in size. It can be brought near to the work place for drilling. A small motor is attached on the drilling machine.

SCREW THREADS

BRITISH STANDARD WHIT WORTH THREADS (B.S.W)

The thread is generally used on bolts and nuts. It is V shaped thread having an angle of 550.

METRIC THREADS

These threads are also V shaped. Threads are kept 600 in metric threads.

SQUARE THREADS

The shape of thread is square. Such threads are less stronger than V shape threads. Wear and tear is also less. These are used in screw jacks.

ACME THREADS

It is modified form of square threads namely trapezium threads. These threads are stronger than square threads. The thread angle of acme threads is 290. On lead screw shaft of lathe, acme threads are used.