Drawings help wonderfully in reasoning out not only correct actions, but also faulty ones, and our readers are earnestly advised to make such faulty drawings in several stages of action. By this course they will educate the eye to discriminate not only as to correct actions, but also to detect those which are imperfect, and we believe most watchmakers will admit that in many instances it takes much longer to locate a fault than to remedy it after it has been found.
Let us now proceed to delineate a fork and roller. It is not imperative that we should draw the parts to any scale, but it is a rule among English makers to let the distance between the center of the pallet staff and the center of the balance staff equal in length the chord of ninety-six degrees of the pitch circle of the escape wheel, which, in case we employ a pitch circle of 5" radius, would make the distance between A and B, Fig. 55, approximately 7-1/2", which is a very fair scale for study drawings.
HOW TO DELINEATE A FORK AND ROLLER.
To arrive at the proper proportions of the several parts, we divide the space A B into four equal parts, as previously directed, and draw the circle a and short arc b. With our dividers set at 5", from B as a center we sweep the short arc c. From our arc of sixty degrees, with a 5" radius, we take five degrees, and from the intersection of the right line A B with the arc c we lay off on each side five degrees and establish the points d e; and from B as a center, through these points draw the lines B d' and B e'. Now the arc embraced between these lines represents the angular extent of our fork action.
From A as a center and with our dividers set at 5", we sweep the arc f. From the scale of degrees we just used we lay off fifteen degrees on each side of the line A B on the arc f, and establish the points g h. From A as a center, through the points just established we draw the radial lines A g' and A h'. The angular extent between these lines defines the limit of our roller action.
Now if we lay off on the arc f six degrees each side of its intersection with the line A B, we define the extent of the jewel pin; that is, on the arc f we establish the points l m at six degrees from the line A B, and through the points l m draw, from A as a center, the radial lines A l' and A m'. The extent of the space between the lines A l' and A m' on the circle a defines the size of our jewel pin.
TO DETERMINE THE SIZE OF A JEWEL PIN.
