Single Spindle Automatic Machines
The principle of working of the single spindle automatic machine is explained by the sectional view of old type of machine as shown in Fig. 34.1. However some refinements have been carried out in it, but the working principle remains the same.
The main drive is from an electric motor at the bottom left hand of the machine which drives a gear box housed in the cabinet base. From gear box the drive is transmitted to the spindle by two roller chains which pass up through the base of bed. Thus the spindle speed can be varied from 60 to 2000 R.P.M. in steps. For turning operations the reverse direction of spindle is employed by use of left hand chain and the slow speed for purpose of screwing and reaming operations is obtained by using right hand chain drive. Spindle reversal is effected by the operation of the clutch on the spindle and for both the left had and right hand chains, fast and slow speed are possible through clutches in the gear box. Thus two forward and two reverse speeds are possible for each combination of pick-off gears. The operation of these and the spindle clutch takes place from the back shaft and thus the speeds could be changed or reversed automatically also.
The spindle is mounted in preloaded [radial roller bearings which prevent excessive clearance in the spindle ever a prolonged
period of operation. On the base of the machine is mounted a bed which carries the main elements of the machine as listed below.
(1) Work spindle
(2) Back shaft (auxiliary control shaft)
(3) Front shaft (cam shaft)
(4) Turret and its slide
(5) Cross-slides (front and rear)
The back shaft and front shaft are mounted, along the bed and carry most of the cams and clutches for the operation of the movements. The back shaft is belt driven at constant speed from the main motor. It carries four sets of clutches which set in motion the movements of the machine elements that are independent of any tool action or cutting. The various movements achieved by these clutches are :
(1) Spindle reversal
(2) Fast and slow speed
(3) Feed and chucking
(4) Turret indexing
The clutches are of the toothed dog clutch pattern, slide on the back shaft and when engaged cause their mating members to route with the shaft. They are actuated by levers which extend across the machine and are pivoted at the centre with their opposite end actuated by trips attached to drums rotating on the front shaft.