Now this line f e is tangent to the arc a from the point f, and consequently a locking placed at the point f is a true tangential locking; and if the resting or locking face of a pallet was made to coincide with the line A f’, such locking face would be strictly “dead” or neutral. The intersection of the line f e with the line A B we call the point C, and locate at this point the center of our pallet staff. According to the method of delineating the lever escapement by Moritz Grossmann the tangent line for locating the center of the pallet staff is drawn from the point c, which would locate the center of the pallet staff at the point h on the line A B.
Grossmann, in delineating his locking face for the draw, shows such face at an angle of twelve degrees to the radial line A f’, when he should have drawn it twelve degrees to an imaginary line shown at f i, which is at right angles to the line f h. To the writer’s mind this is not just as it should be, and may lead to misunderstanding and bad construction. We should always bear in mind the fact that the basis of a locking face is a neutral plane placed at right angles to the line of thrust, and the “draw” comes from a locking face placed at an angle to such neutral plane. A careful study of the diagram at Fig. 88 will give the reader correct ideas. If a tooth locks at the point c, the tangential thrust would be on the line c h’, and a neutral locking face would be on the line A c.
To aid in explanation, let us remove the pallet center to D; then the line of thrust would be c D and a neutral locking face would coincide with the line m m, which is at right angles to the line c D. If we should now make a locking face with a “draw” and at an angle to the line c D, say, for illustration, to correspond to the line c c’ (leaving the pallet center at D), we would have a strong draw and also a cruel engaging friction.
If, however, we removed the engaging tooth, which we have just conceived to be at c, to the point k on the arc a’ a’, Fig. 88, the pallet center D would then represent a tangential locking, and a neutral pallet face would coincide with the radial line A k’; and a locking face with twelve degrees draw would coincide nearly with the line l. Let us next analyze what the effect would be if we changed the pallet center to h’, Fig. 88, leaving the engaging tooth still at k. In this instance the line l l would then coincide with a neutral locking face, and to obtain the proper draw we should delineate the locking face to correspond to the line k n, which we assume to be twelve degrees from k l.