By Tom Parker
Sometimes it costs more to buy it
than to make it from the money itself.
A. 2" clear acrylic drawer front
B. Vertical locking bar
C.–F. Coin disks
G. Coin notch, filed into edge
H. Drive pin (opposite)
J. Nylon washers (opposite)
L. Drive coin
M. Clipped penny
SIMPLE COMBINATION LOCKS ARE
based on a shaft with rotating disks. I made
this one out of 5 quarters, 2 half-dollars, and
a penny (plus an odd assortment of scrap
metal, nuts, and bolts). It looks complicated
but it’s actually very simple.
For illustration purposes, I made the drawer
front out of 2"-thick clear acrylic (A) so you
can see both inside and outside the drawer.
The drawer lock works like this: when
the drawer is closed, a vertical locking bar
(B) made from one of the 50-cent pieces is
moved upward by a cam filed into coin (F),
engaging the roof above the drawer. This
prevents the drawer from sliding open.
Four coin disks — (C), (D), (E), and (F) —
with holes drilled in their centers are aligned
on a coin shaft below the locking bar. These
coins collectively hold the locking bar in place
and keep the drawer locked.
146 Make: makezine.com/26
But each coin also has a notch filed into its
edge (G). It doesn’t matter where on the coin
the notch is filed, but its location becomes
“ 12 o’clock” for the purposes of installing the
drive pins (H) later. Aligning all 4 of these
notches under the locking bar lets the bar
drop, unhooking itself from the roof above the
drawer. This lets the drawer slide open! (The
exact notch dimensions, hole sizes, and pin
widths depend on what sort of hardware you
have on hand.)
So how do you turn the 4 notched coins?
The coin shaft is mounted with one bolt to a
bracket (I) on the inside of the drawer (the
locking bar is bolted to its own separate
bracket). This coin shaft protrudes from the
bracket toward the inside front of the drawer.
The coins are separated with nylon washers
(J) so that each can rotate independently
on the coin shaft. In addition to a notch at
Photography by Tom Parker