65

CONSTRUCTION OF THE
Grand Rapids "Ball Bearing" Hinge Dissected
THREE STEEL BALLS IN EVERY HINGE.

Costs No More than the Ordinary Iron Hinde with Makeshift Buffer. Accept no Substitute. The Steel
Balls used are of the best possible construction, the variation being less than one
thousandth of an inch, thereby insuring uniformity and exactness
and an entire absence of any possible friction.

FIGURE 1 represents the seat arm show-
ing "socket" which fits over the "ball"
on Figure 2 (which represents the upright
desk standard), this constitutes a "ball and
socket," or, as it is termed by some, a
"trunnion joint" hinge. When the seat arm
(Figure 1) is fastened over the standard
(Figure 2) the entire weight rests on the
ball and socket joint--none whatever on the
bolt, it being merely used to clamp the seat
arm and standard together. On both
Figures 1 and 2 you will observe two iron
lugs, which are the stops when the seat is
folded down or up.

FIGURE 3 illustrates reverse side of seat
arm showing inclined grooves in which
three steel bicycle balls run. Figure 4
is a cap which fits over grooves in Figure 3.
You will observe that cap 4 is grooved to
correspond with Figure 3, and when they
are fastened together they form a tube larger
in the middle than at either end, through
which the balls roll as seat is moved up or
down. Figure 5 represents the reverse side
of Figure 4. Notice the face of Figure 5 is
"dished" or concave in shape. When hinge
is put together, a tempered steel washer, A
in Figure 6, fits over the dish in Figure 5.
The different parts are then bolted together
with bolt shown in Figure 6. The tail piece
to caps 4 and 5 passes through hole in stand-
ard (2) maintaining both cap and standard
in one stationary position, the seat arm
moving between them.

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