=60. Sash Pulleys.=—The pulleys for the counterbalancing of
double-hung, or sliding, windows, while apparently unimportant pieces
of hardware, are worthy of much consideration in their selection, and
in the preparation of the specifications care should be exercised to
provide the best pulley consistent with the character of the work. It
is good practice to furnish the millmen with a sample of the pulleys
that are to be used, so that the frame will be properly mortised to
receive them when the sash are hung. By this method, the necessity of
exposing the case to the weather during the erection of the structure
is obviated.
[Illustration: FIG. 67]
The common grades of sash pulleys are rough and cheap, and may be used
for unimportant work and light sashes. For heavier sashes and important
work, however, a better grade of larger and heavier construction should
be used. It is important in specifying sash pulleys to stipulate the
size of the pulley and to specify the diameter of the axle; also to
state whether brass or bronze wheels and bronze faces are desired.
Pulleys are supplied in 1¾-, 2-, 2¼-, 2½-, and 3-inch diameters. The
required diameter of the pulley is determined by the thickness of the
pulley stile and the diameter of the sash weight required to balance
the sash.
[Illustration: FIG. 68]
[Illustration: FIG. 69]
The cases in which the pulleys are mounted in the cheaper grades
are made of cast-iron, while in the better grades they are made of
stamped metal. High-grade pulleys constructed of stamped metal are
also provided; these are put together either by riveting the two faces
of the pulley or by electrically welding them. The construction of a
built-up steel pulley is illustrated in Fig. 67. The cases enclosing
the pulleys are made of cast-iron, as illustrated in Fig. 68 (_a_),
or they are constructed of stamped metal, as shown at (_b_). The ends
of the facing of the case are made square, rounded, or auger-shaped,
and are finished either rough, polished, or lacquered, or are faced
with brass or bronze of any finish desired. The pulleys illustrated
in Fig. 69 (_a_) are so constructed that the mortise in the frame may
be readily formed by a special boring machine carrying three or four
bits. This machine bores holes of a size to fit the several cylindrical
portions of the stamped-metal case, as at _a, a_, a diagram of the
mortising in the frame being illustrated at (_b_).
[Illustration: FIG. 70]
The better grades of pulleys may be procured with semi-steel, brass, or
bronze wheels, and with plain axles or with ball or roller bearings.
In the cheaper grades of sash pulleys, the axles are formed of common
wire, while in the better grades they are made of either steel or gun
metal ⅜ inch in diameter. In the best pulleys, the wheels are turned,
to insure smoothness of motion, and are made with grooves for cord,
ribbon, or chain. All steel pulleys built up as illustrated in Fig.
67 are of recent invention; they run smoothly, and are very easily
applied. These pulleys are also made with ball or roller bearings, and
may be obtained at a reasonable price.
[Illustration: 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.