Watch and Clock Escapements | Page 9

and _N N'_ the cold chisels. The grindstone is supposed to be revolving in the direction of the arrow. The chisels N and _N'_ are both being ground, but the chisel _N'_ is being cut much the more rapidly, as each particle of grit of the stone as it catches on the steel causes the chisel to hug the stone and bite in deeper and deeper; while the chisel shown at N is thrust away by the action of the grit. Now, friction of any kind is only a sort of grinding operation, and the same principles hold good.
THE NECESSITY FOR GOOD INSTRUMENTS.
It is to be hoped the reader who intends to profit by this treatise has fitted up such a pair of dividers as those we have described, because it is only with accurate instruments he can hope to produce drawings on which any reliance can be placed. The drawing of a ratchet-tooth lever escapement of eight and one-half degrees pallet action will now be resumed. In the drawing at Fig. 18 is shown a complete delineation of such an escapement with eight and one-half degrees of pallet action and equidistant locking faces. It is, of course, understood the escape wheel is to be drawn ten inches in diameter, and that the degree arcs shown in Fig. 1 will be used.
We commence by carefully placing on the drawing-board a sheet of paper about fifteen inches square, and then vertically through the center draw the line _a' a''_. At some convenient position on this line is established the point a, which represents the center of the escape wheel. In this drawing it is not important that the entire escape wheel be shown, inasmuch as we have really to do with but a little over sixty degrees of the periphery of the escape wheel. With the dividers carefully set at five inches, from a, as a center, we sweep the arc n n, and from the intersection of the perpendicular line _a' a''_ with the arc n we lay off on each side thirty degrees from the brass degree arc, and through the points thus established are drawn the radial lines _a b'_ and _a d'_.
[Illustration: Fig. 18]
The point on the arc n where it intersects with the line _b'_ is termed the point b. At the intersection of the radial line _a d'_ is established the point d. We take ten and one-half degrees in the dividers, and from the point b establish the point c, which embraces the arc of the escape wheel which is utilized by the pallet action. Through the point b the line _h' h_ is drawn at right angles to the line _a b'_. The line _j j'_ is also drawn at right angles to the line _a d'_ through the point d. We now have an intersection of the lines just drawn in common with the line _a a'_ at the point g, said point indicating the center of the pallet action.
The dividers are now set to embrace the space between the points b and g on the line _h' h_, and the arc f f is swept; which, in proof of the accuracy of the work, intersects the arc n at the point d. This arc coincides with the locking faces of both pallets. To lay out the entrance pallet, the dividers are set to five inches, and from g as a center the short arc o o is swept. On this arc one degree is laid off below the line _h' h_, and the line g i drawn. The space embraced between the lines h and i on the arc f represents the locking face of the entrance pallet, and the point formed at the intersection of the line g i with the arc f is called the point p. To give the proper lock to the face of the pallet, from the point p as a center is swept the short arc r r, and from its intersection with the line _a b'_ twelve degrees are laid off and the line b s drawn, which defines the locking face of the entrance pallet. From g as a center is swept the arc _c' c'_, intersecting the arc n n at c. On this arc (_c_) is located the inner angle of the entrance pallet. The dividers are set to embrace the space on the arc _c'_ between the lines _g h'_ and g k. With this space in the dividers one leg is set at the point c, measuring down on the arc _c'_ and establishing the point t. The points p and t are then connected, and thus the impulse face of the entrance pallet B is defined. From the point t is drawn the line _t t'_, parallel to