03-12-2012, 12:30 PM
Backgeared headstock
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ABSTRACT
Backgeared headstock consists of Casing in which spindle, three or four step cone pulley & back gears are accommodated.
When backgear is engaged the spindle speed reduces considerably. Slow speed is necessary for following reasons –
In turning jobs of large diameter within the available cutting speed of the material.
In turning the jobs of tough or hard material
In operations like Drilling, Milling
In taking deep cut as in through turning.
A step cone pulley is mounted on main spindle, which carries a spur gear G1 at its one end & pinion P1 at the other end. Gear G1 is firmly keyed to the spindle, hence it cannot revolve freely. Spindle carries a sleeve over it which is a loose fit. The cone pulley & pinion P1 is attached to this sleeve. Due to this cone pulley & pinion P1 rotates simultaneously. A spring knob K engages the gear G1 with the cone pulley. Cone pulley is driven by belt through countershaft by an electric motor. This type of arrangement will give four different speeds of the spindle.
The backgears are mounted on eccentric shaft which is operated by a hand lever known as ‘Backgear engaging lever’ (L) .The backgear consist of a spur gear G2 (opposite to pinion P1) & a pinion P2 (opposite to gear G1).
When speed reduction is desired, the knob is pulled out to make the cone pulley free of gear G1 & hence of the spindle.
The backgears are put into mesh with the spindle gears by pulling in the eccentric shaft.
Now sequence of transmission of motion and power is such that the cone pulley is driven by the motor through belt. Due to this P1 revolves.This, being in mesh with gear G2, transfers motion to the latter which, in turn revolves the eccentric shaft & hence the pinion P2.This,further being in mesh with gear G1,transmits the motion to the latter & hence to the spindle.