FIG. 40.
To construct a tappet for a plain cloth from the following dimensions.—Lift of tappet, 4 inches. Distance from centre of shaft to nearest point of contact with treadle bowl, 2 inches; dwell one-third of a pick. Diameter of treadle bowl, 2 inches.
At a radius of 2 inches describe the circle A ([Fig. 40]). This circle represents the distance from the centre of the shaft to the nearest point of contact with the treadle bowl.
At a radius of 3 inches describe the circle B. One inch added for radius of treadle bowl.
At a radius of 7 inches describe the circle C. Four inches added for lift.
The circle B represents the centre of the treadle bowl when the inner circle of the tappet is acting upon the bowl.
The circle C represents the centre of the bowl when pressed down by the tappet.
The pattern being a plain one, the circle must be divided into two equal parts, and each half-circle will then represent one pick. By the line DE divide the circle into two equal parts. Then, as the healds must have a pause or dwell equal to one-third pick when at the top and bottom of their stroke, divide each half-circle into three equal parts by the lines FK, GH. Divide FH and GK each into six equal parts, and divide the space between the circles B and C into the same number of unequal parts, the largest being in the middle, gradually decreasing towards the circles B and C.
From the corners of these unequal spaces, and with the radius of the treadle bowl in the compasses, describe circles representing the position of the treadle bowl at different parts of its movement.