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Laying Out the Escapement (We must first determine)

In laying out the escapement we must first determine the size of the escape wheel and also the number of teeth it is to have. We will make our drawing larger than the actual work is to be, and then after taking our measurements direct from the drawing, reduce them to the actual working size. In Fig. 5 the diameter of the escape wheel is three inches and has thirty teeth revolving to the right, so that we may mount a seconds hand upon the arbor if used with a seconds pendulum. In making a draft of any kind all the lines should first be drawn in with a lead pencil, and then those lines which are to remain are to be inked in with any good waterproof India ink, Higgins' American drawing ink being an excellent article for the purpose. With the dividers set with a radius of one and one-half inches, draw a circle which will represent the diameter of escape wheel. The distance between one tooth and the next equals three hundred and sixty degrees (the number in a complete circle) divided by thirty, the number of teeth in our escape wheel, which will give us twelve degrees as the required distance (360<??>30=12). The distance between the center of the escape wheel and the center of the anchor equals the radius of the escape wheel plus four tenths of this radius, 1 1/2 = 3/2, 4/10 of 3/2 = 6/10 and 3/2 + 6/10 = 21/10 = 2 1/10 the distance required. This distance is to be increased or diminished inversely according as it is desired to reduce or increase the oscillation of the pendulum. Draw a line joining the center of the anchor and the center of the escape wheel, which is the center line of the escapement. In laying off the teeth begin at this center line, laying them off on either side until completed. The back of the teeth are to be radial, while the front faces are to be of an angle sufficiently great to give the teeth strength, yet not so great that more than the point of the tooth will at any time strike the pallet. When this angle has been decided upon, draw a line representing the front face of a tooth and extend it beyond the center of the escape wheel. Now draw a circle to which this line will be a tangent, and all that is necessary in order to draw in the rest of the teeth is to place the straight edge so as to coincide with the point of a tooth and this circle. From the center of the anchor draw a circle of a radius equal to half the distance between the anchor and escape wheel centers. As the anchor is to embrace eight teeth, we draw lines which are tangent to this circle, and touching the points of the fourth tooth on each side of the center one, which will give the pallet faces, if they were left flat. By curving the faces of the pallet and giving an angle to the front faces of the teeth, the friction is disengaging, consequently will wear better. This escapement is sometimes made to embrace ten teeth instead of eight.