O Scale Trains Magazine Online

earing hinges from the scoop assembly, namely a Dremel (or
similar) tool with a thin cutoff wheel or circular saw blade. A
4
fixed model saw, or circular-type saw with a two inch Gyros
blade attached works, too. The idea here is to preserve the maximum
thickness on the side bearing hinge assembly, because it
will be used in the future. It is also necessary to get an precise
parallel cut along the long axis on the scoop. The Gyros blades
are approximately 0.007” thick, whereas Dremel’s small cutoff
wheel, in its virgin state, is 0.022” thick. I like to save my old
Dremel cutoff wheels that have been “pre thinned” by side cutting
in a polishing mode. These can be thinned down to 0.018”,
which is sufficient for this project. For better control while cutting
the scoop assembly, solder it to a brass plate. This, in turn, is
used to fixture the assembly for cutting, whether using a Dremel
tool or a fixed circular saw. The idea here is to have as many fingers
after the cut as you had before the cut. Figure 1 shows both
the scoop assembly and the bottom plate control rod assembly
before and after cutting.
Now, we need to drill a whole bunch of holes to serve as
bearings for the various hinge pins. Figure 2 shows the location
and size of these holes. It is important that your bearing joints
have no “slop”; the amount of motion is so slight and freeplay
in each successive joint is additive. If your joints have too much
play, by the time the motion gets from the scoop down to the
cylinder piston there will be no apparent motion in the cylinder.
I encountered this problem and I reversed it by making the hinges
as tight as possible. To keep things as slop-free as possible, I
used 0.024” diameter piano wire for all of the hinge pins, and
use clearance drill #70 for the holes.
Now, drill the forward control yoke and the plate itself for the
insertion of the control rods. These are larger holes, and probably
a #58 or #56 drill should be used for these. The clearance
here is actually not critical and should be fairly loose to provide
for smooth motion. I used 0.042” brass round stock here, which
is available from K&S at most hobby shops. I use Radio Shack
silver bearing solder (0.015” diameter, part number 64035e) and
Oatey liquid soldering flux to prep surfaces.
Figure 3 shows the assembled and fabricated control rod/
yoke assemblies, as well as the completed working scoop. It is
important not to wick any solder down the hinge pin into the
main scoop body. To prevent this, I coat the holes in the body
with oil. You can also just use a little bit of solder and control
your heat. For this job I used a Link LPT200 micro-torch which I
purchased from Home Depot for about $20.00. This is a sturdy
instrument, takes a great deal of abuse, has a controllable flame,
July/Aug ’06 - O Scale Trains •