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2 The critical parts of the machine are subjected to dyt~amic stresses whilst the shearing is in operation. The magnitude of the stress at any location changes as the cutting progresses from one point to another. The machine experiences repetitive stresses if the shearing is in the continuous mode of operation. The main aim of the present paper is to study this aspect of dynamic behaviour. The dynamic beh~'viour is also compared with quasi-static behaviour which is based on the simplifying assumption that the total response is the super- position of a number of static responses with the cutting force at different locations.
Since the force needed for shearing is known and since the shearing process is gradual, the work done during cutting is determined easily. Since the duration of cutting is a fraction of the time taken for one revolution of the eccentric shaft, the fluctuation in speed likewise is determined easily. From the maximum energy consumed during cutting, the Horse-power requirement of the prime mover is estimated. Once the speed of the intermediate shafts is assumed, design of the shaft and the associated anti-friction bearings is a straightforward exercise. The only further complex parts of the machine for which detailed analysis is called for are the stationary housing, consisting of the two side-stands, the hold-down, the bottom plate and the moving blade-carrier.
The blade of the guillotine shear is inclined at an angle to the horizontal in order to enable gradual cutting of the plate. This helps in reducing the shear area at any instant of time, as shown in Fig. 1, For a plate to be cut of thickness t, the width of cut at any instant of time is t/tan ct. Since this will be small in comparison with the maximum width to be cut (w), the cut takes place over a finite period of time. If the mean velocity of the blade is v, then the total time needed for cutting the maximum width of the plate is: T= w tan ct/v The cutting force experienced by the blade is given by: F= t-'r/tan z~ (2) where r is the ultimate shear strength of the material.
In the case of the over-crank shear (Fig. 2), the eccentric shaft is located in the top half of the shearing machine along with the connecting link and the bladecarder. The line of stroke of the blade passes through the centre-line of the eccentric shaft. In the case of the under-crank shear (Fig. 3), the eccentric shaft is located in the bottom half with the blade-carrier in the top portion. Hence the height of the over-crank shear is always greater than that of the under-crank shear. Moreover, in the case of the under-crank shear, there is an offset (e) between the line of stroke of the blade carrier and the center-line of the eccentric shaft, the offset being due to the space below the bottom-dead-center position of the moving top blade being occupied by the stationary bottom blade.

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