1f. Mark and drill 3 equidistant screw holes in the
body for each ring, without
the rings inside. Then slide in
the barrel assembly, mark the
rings through the holes, and
drill them with small holes
for the self-tapping screws.
1f
1h 1h
2a
2a
NOTES: Later you’ll
install a longer bottom
screw in the rear centering
ring.
1g. Machine the end cap
from cutting-board plastic to
fit snugly inside the body. Drill
a centered 8mm hole in the
cap for the plunger to pass
through, and chamfer the
front with a countersink bit
to let it exit easily. Mount an
8mm fender washer onto its
back using 2 small screws. 1g
The washer provides
a hard-wearing metal
surface for the catch
wire to slide against.
1h. For the catch wire, cut
4" of the 1.2mm wire. Drill and
thread it through the end cap
and washer. Bend the front
of the wire, or attach a small
stop, so it won’t pull out. Bend
the back of the wire to lie
flush across the end cap.
Drill and mount the end cap
in the body the same way you
did with the centering rings.
TIP: Old printers and
scanners are a great source
of small-diameter steel
rods that machine well.
2. PISTON AND PLUNGER
2a. Machine the piston out
of more cutting-board plastic
to slide within the body. Cut
an O-ring groove around its
perimeter to provide a seal.
Gregory Hayes (1g, 2a top)
The telescoping plunger
is made from a 96mm-long
7" tube. A short, wide screw
holds it to the piston. I soldered mine, but you can also tap
threads in the tube and screw
it in. A small O-ring under the
screw helps seal the piston.
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