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.

[Illustration:  Fig. 56]

To make the situation better understood, we make an enlarged drawing of the lines defining the jewel pin at Fig. 56.  At the intersection of the line A B with the arc a we locate the point k, and from it as a center we sweep the circle i so it passes through the intersection of the lines A l’ and A m’ with the arc a.  We divide the radius of the circle i on the line A B into five equal parts, as shown by the vertical lines j.  Of these five spaces we assume three as the extent of the jewel pin, cutting away that portion to the right of the heavy vertical line at k.

[Illustration:  Fig. 57]

We will now proceed to delineate a fork and roller as the parts are related on first contact of jewel pin with fork and initial with the commencing of the act of unlocking a pallet.  The position and relations are also the same as at the close of the act of impulse.  We commence the drawing at Fig. 57, as before, by drawing the line A B and the arcs a and b to represent the pitch circles.  We