BACK GEAR & TUMBLER GEAR MECHANISM (MP-I)

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for 3rd sem mechanical students

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SAL TECHNICAL CAMPUS:

SAL TECHNICAL CAMPUS SAL COLLEGE OF ENGINEERING

MANUFACTURING PROCESS-I:

MANUFACTURING PROCESS-I BACK GEAR MECHANISM AND TUMBLER GEAR MECHANISM PREPARED BY : SAGAR TUNDIYA MECHANICAL (PA-3) ENROLLMENT NO.: 151130119083 GUIDENCE BY : BHAVIK PADHIYAR

BACK GEAR MECHANISM:

BACK GEAR MECHANISM USE OF BACK GEAR MECHANISM For winder range & higher reduction of spindle speed, back gear mechanism is used. back gear mechanism is an additional part of the belt drive lathe. It is used to obtain slower & wider range of spindle speed back gear disengagement & engagement is shown in fig. Back gear are located on the back of cone pulley in the fig.

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Diagram-of-the-Driving-Mechanism-of-a-Triple- Gear

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As its name implies, "back gear" is a gear mounted at the back of the headstock (although in practice it is often located in other positions) that allows the chuck to rotate slowly with greatly-increased turning power. For a novice the ability to run a work piece slowly might seem unnecessary, but a large-diameter casting, fastened to the faceplate and run at 200 r.p.m. (around the bottom speed commonly found on a lathe without back gear) would have a linear speed at its outer edge beyond the turning capacity of a small lathe. By engaging back gear, and so reducing r.p.m. but increasing torque, even the largest faceplate-mounted jobs can be turned successfully. IMPORTANCE OF BACK GEAR MECHANISM IN MACHINE

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Screw cutting also requires slow speeds, typically between 25 and 50 r.p.m. - especially if the operator is a beginner, or the job tricky. A bottom speed in excess of those figures (as found on most Far Eastern and some European "Continental" machines) means that screw cutting - especially internally, into blind holes - is, in effect, impossible. These lathes are advertised as "screw cutting" but what that really means is just power sliding - a power feed along the bed. With these machines, even if you go to the trouble of making up a complex pulley system to reduce the spindle speed (like the early Atlas 9-inch), you will find the torque required when turning large diameters at slow speeds causes the belts to slip.

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The only solution is a gear-driven low speed - and so a properly-engineered small lathe, with a back gear fitted, not only becomes capable of cutting threads but can also tackle heavy-duty drilling, big-hole boring and large-diameter turning and facing; in other words, it becomes possible to use it to the very limits of its capacity and strength. To show how important back gear has always been considered, examine the specification of the many small English-made metal turning lathes made from the mid 19th century onwards: nearly every one was so equipped.

MECHANISM:

MECHANISM Back gears (BG) mounted on an eccentric shaft.   Handle to rotate an the eccentric mounting shaft and so engage the back gears   Pin (P) to connect and disconnect Bull Wheel and V-pulley. Instead of a pin, some lathes use a stud and nut arrangement - or even a quick-release fitting.   Bull Wheel (BW) - in this case with a ring of useful indexing holes, the locating plunger passing through the front face of the headstock casting

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The back gear is a clever but essentially simple mechanism probably conceived around 1817 by Richard Roberts, an English engineer and prolific inventor. If you have to read the following several time to understand how it works, don't worry, everybody does…. In the picture above (a 1934 Atlas lathe) the 4-step V-pulley (V) has a small gear (SG) permanently attached to its smaller end. The entire length of V-pulley and gear are bushed - and able to rotate freely on the headstock spindle.

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The large "Bull Wheel" (BW) is keyed or held to the spindle with some sort of through-bolt or grub screw and always rotates with it. It can be connected to the V-pulley - and disconnected from it - by a pin (P) which is often spring-loaded, or by a nut and stud arrangement. In normal use the V-pulley is rotated by the drive belt and the spindle turned through the action of the pin driving the Bull Wheel and hence the spindle to which it is connected.

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To engage back gear the lathe is stopped, the pin (P) withdrawn (leaving the pulley and small gear free to rotate) and the Back gear (BG) rotated on its eccentric shaft to bring it into mesh with the other gears. On starting the lathe the action is now as follows: the pulley is rotated by the drive belt with the small gear (SG) on the V-pulley (V) driving the larger of the two rear-mounted back gear mechanism

TUMBLER GEAR MECHANISM:

TUMBLER GEAR MECHANISM DEFINATION THE GEAR MECHANISM OPERATED BY MEANS OF THE FEED REVERSE LEVER IS CALLED THE “ TUMBLER REVERSING MECHANISM ”.

USE OF TUMBLER GEAR MECHANISM:

USE OF TUMBLER GEAR MECHANISM Usually to change the direction of feed rod and lead screw tumbler gear mechanism is used. The carriage can be moved from headstock end to tailstock from tailstock end to headstock end automatically by engaging the tumbler gear. And the tumbler gear is used while thread cutting and automatic feeding. You can refer the image provided below for various parts of tumbler gear mechanism.

Slide15:

The tumbler Gear Mechanism can be described as an arrangement of gear wheels which is used to reverse the direction of rotation of any machinery. In this mechanism, the technique used is, increasing the number of engaged gear wheels which can easily be performed by pulling a liver. In some industries or manufacturing units, where thread cutting, or similar activities which requires automatic feeding, this mechanism is used.

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FRONT VIEW SIDE VIEW

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In its neutral, central position it allows the headstock spindle to revolve without driving any of the gears. Moving the engagement lever up or down (the spindle must be stationary of course) engages one or other of a pair of tumble gears below the spindle gear causing the next gear in the train to revolve either clockwise or anticlockwise. The lever is usually, but not always, spring loaded in some way, with a plunger that engages in one of three holes in either the front or side face of the headstock. On all types, the stud gear is made removable, allowing it to be part of the screw cutting train or set up, as very small gear, to give a fine feed to the carriage MECHANISM

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E -> gear attached to spindle A, B -> tumbler gears M -> lever D -> stud gear   Spindle gear always rotates in clockwise direction. Tumbler gears are fitted in a bracket. Through the set odd intermediate gears, the stud gears re connected to lead screw gear.

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Thank You

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