376 Machine Drawing
dharm
d:\N-Design\Des19-1.pm5
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
