Fig. 1471.
[Fig. 1471] represents a Brown and Sharpe bevel protractor, with a pivot and thumb-nut in the middle of the back with a half-circle struck from the centre of the pivot and marked to angular degrees. The pointer for denoting the degrees of angle has also a thumb-screw and nut so that the blade may, by loosening the pivot and pointer, be moved to project to the required distance on either side of the back.
Fig. 1472.
Swasey’s improved protractor, however, is capable of direct and easy application to the work, forming a draughtsman’s protractor, and at the same time a machinist’s bevel or bevel square, while possessing the advantage that there is no protruding back or set-screw to prevent the close application of the blade to the work. This instrument is shown in [Fig. 1472]. The blade a is attached to the circular piece d, the latter being recessed into the square b b, and marked with the necessary degrees of angle, as shown, while the mark f upon the square b serves as an index point. The faces of a, b b, and d are all quite level, so that the edges will meet the lines upon the work and obviate any liability to error. The piece d is of the shape shown in section at g, which secures it in b b, the fit being sufficient to permit of its ready adjustment and retain it by friction in any required position. The dotted lines indicate the blade as it would appear when set to an angle, the point e being the centre of d, and hence that from which the blade a operates.
