Fig. 71
There is a special type of sash pulleys that may be used for twin and triple windows, where it is necessary to form a narrow mullion between the windows. This pulley is known as the Grant overhead sash pulley, and is used as illustrated in [Fig. 70]. At (a) is a twin-window arrangement, showing the sash on the two sides double-hung, each sash being counterbalanced by means of one counterweight. By this means, the frame mullion between the two sashes can be made as narrow as 2 inches, which is an advantage where the maximum amount of daylight opening is desired. Frequently, in triple windows, the center sash, as well as the two side sashes, is made double-hung. In such a case, the arrangement of the overhead pulleys would be as shown in [Fig. 70 (b)]. These pulleys provide a convenient means for arranging double-hung windows of this type, but sufficient room must be left in the head of the window to allow for the insertion of this pulley and the travel of the sash counterweights. The construction of this type of overhead pulley with roller bearings is shown in [Fig. 71].
61. Determination of Size of Sash or Frame Pulleys.—The architect’s specifications should stipulate the diameter of the sash pulleys to be used in the work, and this item requires careful consideration. Where care is not exercised in this regard, either the pulleys will be so small that the weight will rub against the pulley stile, or they will be so large that the weight will rub the jamb casing on the opposite side of the pocket. Standard sash pulleys are made in sizes from 1¾ to 3 inches in diameter, varying by quarter inches. In determining the diameter of the pulley required for a particular window frame, a good rule is to multiply the thickness of the pulley stile by 2.25; thus, a ⅞-inch stile would require a 2-inch pulley; a 1⅛-inch stile, a 2½-inch pulley; and a 1⅜-inch stile, a 3-inch pulley. It is best to specify that pulleys for metallic frames shall be of the larger size, namely, 3 inches in diameter; and also that these pulleys shall have ⅜-inch axles.
62. Sash Cords and Chains.—The sash cords by which the sashes are attached to the counterweights in double-hung windows are usually furnished by the carpenter, and are so specified. However, they may be specified under hardware. The specification for the sash cord should state both the size and the maker’s name, and for good standard work Sansom Spot or Silver Lake sash cords are the best that can be procured. [Table VI] will be found convenient in determining the diameter of the cord and the consequent size by number, as well as the size of the sash pulley.
TABLE VI
STANDARD SIZE OF SASH CORD FOR PULLEYS
Sash chains are made in the form illustrated in [Fig. 72], and may be had either in steel, red metal, or bronze. The sash chains in the market are usually made in four sizes, being numbered from 0 to 3. The makers, however, have no agreement regarding these standards, so that the numbering is not uniform; one manufacturer’s No. 0 chain may be his heaviest make, while a chain of the same number furnished by another maker may be the lightest chain that he manufactures. In order to provide against this discrepancy when specifying, it is well to name the maker of the chain. The lightest sash chain will support sashes weighing from 40 to 75 pounds, while the heaviest will carry sashes that weigh from 150 to 250 pounds.
Fig. 72