2.17.
This is the most adaptable and commonly used non-precision instrument to be used in layout
and inspection work (Fig. 2.74).
The combination set consists of scale, squaring-head, protractor and centre-head. It consists
of a heavy scale, which is grooved all along its length. It is on this groove that sliding squaring head
is fitted. One surface of the squaring head is always perpendicular to the scale and it can be adjusted
at any place by a locking bolt and
nut. The squaring head also con-
tains a spirit level which is used to
test the surfaces for parallelism.
For laying out dovetails an in-
cluded angle is also mounted on the
scale. It can also slide to any posi-
tion and be locked there. A scribing
point is also inserted into the rear
of the base for scribing purposes.
The squaring head and scale can be
used for height and depth measure-
ments, inside and outside squaring
operations.
The centre head attachment is used with the scale to locate the centre of bar stock. For
locating the centre, the part to be centred is held beneath the scale and against the sides of the
Fig. 2.74. Combination Set.
centre head. Three lines are drawn along the scale by rotating the part every time. Thus three lines
given three points of intersection. The middle point of the triangle is the centre of part.
The protractor is also capable of sliding along the scale. It contains a semi-circular disc
graduated from 0 to 90° on either side of centre. For the purpose of levelling a surface or checking
an inclined plane the protactor head also contains a spirit level. With the help of protractor, the
correct angle of the work can be set on it and deviation of work from this angle can be checked by
inserting a feeler gauge between the blade and the part to be inspected.
2.17.1.
Combination Sets with square head, center head and nonreversible protractor head and blade.
(Refer Fig. 2.75) With reversible lock bolts, scriber, spirit level in both square
head and protractor head, direct reading double 180° protractor scale, and hardened steel,
machine-divided blade. Also available with satin chrome blade and protractor head. Cast iron heads
with black wrinkle finish.
Fig. 2.75. Combination set.
