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THE OPERATING PRINCIPLES OF INDEXING TURRET AND SLIDING HEADSTOCK & THEIR SUITABLE APPLICATIONS

TURRET AND ITS OPERATING PRINCIPLE

The turret is an essential component of an industrial machine known as the indexing turret. It operates by fluid power and uses ratchet and pawl mechanism. A cylinder moves a gear ratchet assembly which is immersed with a pinion gear keyed to a shaft on which the turret is mounted, thus the linear movement of cylinder rotates the turret by a pre-determined amount to the next indexing position. The rack assembly is arranged in a pair parallel to each other either side of the pinion.

In the design, only one rack contacts the pinion by another parallel cylinder mounted at right angle to the previous power cylinder. It is possible to make one of the two racks engage with the pinion. The forward and backward stroke of the main cylinder can be utilized to rotate the turret in the same direction.

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An arrangement can be made to govern the feed rate of the main cylinder. In such arrangement, a divided wheel having indexed holes on its periphery is also mounted along with the turret.

THE OPERATING PRINCIPLE OF SLIDING HEADSTOCK

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The sliding headstock has a similar working principle in all industrial machines. The sliding head type of a single spindle in an automatic machine is explained by the sectional view of the old type of machines. Though some refinement has been made on a modern sliding stock, its working principle remains the same.

Machines using the component are mainly meant for the manufacturing of sets of quantities of small, precision components, and is often referred to as Swiss Auto, therefore, they are suitable for areas where work is long and slender and where accuracy, finish, and concentricity is important.

Some of the headstocks that are traversed by a ball or plate type CAM, a troll bracket supporting five-tool slides and each slide operated by a separate cam, are mounted in the center. In such, their tool bracket also contains a guide or steady bush for the bar stock.

In most designs, cams are held on a front camshaft. These control the tool slides and headstock movements. In a place of a turret, the slide can be mounted in a feed base having single or multi-spindle for operations like drilling, reaming, screwing, tapping, etc. the main drive is from an electric motor at the bottom left hand of the machines which drives a gearbox housed in the cabinet base.

From gearbox, the drive is transmitted to the spindle by two roller chains which pass up through the base of the bed. This spindle speed can be varied from 60 to 200RPM in steps. For turning operations, the reverse direction of the spindle is employed by use of hand and the slow speed for purpose of screwing and remaining operations is obtained by using right-hand chain drive.

Spindle reversed is obtained by the operation of the clutch on the spindle and for both the left hand and right-hand chains, fast and slow speed are possible through clutches in the gearbox. 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 preload roller bearings which prevent excessive clearance in the spindle over a prolonged period of operation. On the base of the machine, there is a bed mounted on it which carries the main elements of the machine as listed below:

  • Work spindle
  • Back shaft (auxiliary control shaft)
  • Front shaft (camshaft)
  • Turret and its slide
  • Cross-slides (front and rear)

The back shaft and front shaft are mounted along the bed and they carry most of the cams and clutches for the operation of the movements. The back shaft is driven at constant speed from the main motor. It carries four sets of clutches which set in motion of the machine elements that are independent of any tool action or cutting. The various movements achieved by these clutches are;

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Spindle reversal

Fast and slow speed

Feed and chucking

Turret indexing

 

The clutches are of the toothed dog clutch pattern, slide on the back shaft and when engaged cause their mating members to rotate with the machines and are pivoted at the center with their opposite and actuated by trips attracted to drums, rotating on the front shaft via a cycle time change gears.

The headstock moves the rotating bar past the tools filter longitudinally on tool bracket. All these tools can move independently in or out transversely. The tools could either move in the ratio of 1:1 with the cam throw or in different ratio through adjustable levers.

It will be seen that tool 1and 2 are mounted on the front and rear of the rack or operated as a single cam and thus these cannot be used together. Tool no.1 is recommended for plain turning only, the other tools being used for part off, forming, etc. the tool bracket holds a guide bush through which the bar passes giving a high degree of stability and steadiness during machining and also permitting bar to be mounted as cantilever for machining operations.

The tool mounted on feed base can be given rotary motion. Thus, though bar may be rotating at constant speed for turning but still operating. Screwing can be done at a slow speed by differential principle of machining because relative cutting speeds is the difference of speed of bar and speed of taps or die head in feed base.

Right hand threads are cut by revolving die head faster than work spindle and left hand threads by revolving die head slower than work spindle. One multi-spindle feed bases, each spindle ca be indexed in line with the work axis required.

In this type of machines, no special bar stop is required because the headstock itself traverses. The parting off tool is left in the forward position after cutting through the bar in previous operation. The chuck opens and the headstock moves back, the bar being preloaded moves forward against the parting off too. When the headstock has reached its initial position, the chuck grips the bar. The parting off tool retracts and the work cycle commences.

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Originally posted 2018-10-03 10:01:15.

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