Machine Drawing

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376 Machine Drawing


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When the handle is operated, the two jaws are moved towards or away from the V-block, by


turn-buckle principle. However, to ensure positive movement of the jaws, the translatory movement


of the screws 5 and 6 is arrested by means of locating pin 10; the square head of which fits into the


corresponding groove in the collar of the screw. Two tenons (not shown) are fitted to the base of


the body to ensure proper alignment of the vice axis with respect to the machine spindle axis.


19.3.7 Milling Fixture


Figure 19.14 shows a simple milling fixture. The fixture is located on the machine table by two


tenons 7 and clamped to the machine table in the T-slots. The workpiece is located using the full


diameter locating pin 8 and flattened locating pin 4. The job is clamped by two heavy duty clamps


2 to the fixture base.


The cutter setting is obtained by using the setting block 3, for both depth and transverse


setting. The setting block is fixed by means of locating pins 9 and dowel pins 10. The clamps are


positioned by guide pin 11 and rigidly fixed by clamping screws 5 and clamping nuts 6.


19.3.8 Indexing Drill Jig


Drill jigs are used when it is necessary to move the workpiece, relative to the machine spindle,


between machining operations. The workpiece is located and clamped to a movable member,


which can be indexed to the required position, relative to the drill bush and then locked while each


feature is machined.


Figure 19.15 shows a simple indexing drill jig to produce four radial holes in the work-


piece. The jig body 1 is equipped with an indexing lever 3 for locking the job in the required


position. The rotating pin 5 and the indexing plate are located and clamped to the jig body, by


means of a locking screw 4. The jig body is also provided with bush plate 2, which accommodates


drill bush 7, for guiding the drill bit. For quick loading and unloading the job in the jig, C-washer


8 and clamp 6 are used. Locating pin 9 and dowel pins 10 are used for proper location and fixing


of bush plate in the jig body.


After locking the rotating pin by the indexing lever and the locking screw, a radial hole is


drilled. The job is indexed to the next position by loosening the locking screw and disengaging the


indexing lever. The rotating pin (with index plate and job) is indexed to the next position and


locked. The procedure is repeated till all the four radial holes are drilled. The spring is held in


position, by the spring retainer 10.


19.3.9 Pierce and Blank Tool


The pierce and blank tool illustrated in Fig. 19.16, used for the production of washers, is a follow-


on type. It consists of a cover plate 3, which is located relative to the base 1 by means of guide pins


8 and guide block 7. The punch 5 and the blanking tool 6 are located in the tool holder 4 which is


finally held by the cover plate.


The die block 2 is fixed to the base, relative to the tool holder and tools. The hole in the feed


stock is pierced by the punch first and then the feed stock is positioned under the blanking tool


which shears the washer. One washer is completed at each stroke of the press. The hole left by the


blanking operation is used to position the stock against the spring loaded stop 9.


19.4 Miscellaneous Parts


19.4.1 Blow-off Cock


This is used to remove sediments collected at the bottom of a boiler. When operated, water rushes


out from the boiler (being under pressure) carrying the sediments along with it. The blow-off cock


is fitted at the lowest part of the boiler, where the sediments are expected to collect. The side

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