Pennsy Class G22 Gondola in S Scale
Last update: October 10, 2004
The PRRPro gang's
latest project is a Pennsylvania Railroad G22 gondola. A good portion
of the group is in HO
or N and have just about everything available to them as either kits or
RTR. Particularly the HO guys given the incredible range of Pennsy
resin kits put out by Westerfield. In any case, for me to join in on
the fun I have one option - scratch building. A gondola is a pretty
simple car so
hopefully I can keep up.
I will attempt to update this page as I make progress. If you have any
questions email me.
The overall plan for this project is to create a set of master patterns
and then cast the car parts in resin. 
This
will allow me 1) to only
build one side and end of the car and 2) to make multiple copies for
myself and friends. After all, you can't have only one gondola! I used
a
similar process to build a PRR H21 open
top hopper fleet.
Part 1 - Making the gondola side
Part 2 - Ends and floor
Part 3 - Finishing up
Part 1 Making the gondola side
July 22, 2004
My G22 project started by creating a CAD drawing of the side. Being a
simple rectangle, this was pretty straightforward. The drawing included
reference lines for the placement of the vertical support
ribs and lines for the bottom rows of rivets. The drawing was created
in full size. The CAD program can scale to what ever I wish for
printing. I used this feature to print an S scale drawing on a sheet of
0.010" styrene using my ALPS printer. Since this is not an ink-jet
printer the printed material does not smear on the sheet when handled.
The CAD program that I use is Cadrail from Sandia Software. Cadrail is
a general purpose 2D CAD package with some added features to help in
the design of model railroad layouts. For the G22 drawing, only simple
2D
line drawing was needed and it only took about 15 minutes to complete.
Of
course having a measured drawing to take dimensions from is critical
for this stage. Help arrived from a kind member of the PRRPro list!
July 23, 2004
Once the drawing was printed on the styrene sheet, I mounted the
sheet
on my
"riveter". My setup for creating rivets consist of mounting a Northwest Short Line Sensipress on the
tool platform of my Sherline
lathe. 
This allows me to
move the Sensipress in both X and Y axis
with great accuracy and repeatably. In this configuration, the sheet to
be riveted is fixed relative to the lathe. The placing of rivets is
simply a matter of figuring where they should go, and dialing to that
location. The locations of the rivets were derived from a builders
photo. Using known dimensions I was able to roughly guess where the
rivets needed to be. I spaced the horizontal rows of rivets 0.080"
(about 5") apart, the vertical positions varied. An effort was
made to keep the side of the gondola parallel with the lathe. This
would make riveting the horizontal rows a matter of just cranking
0.080" increments. The reference lines printed on the sheet allowed me
to adjust for errors.
I used the .015 die for the G22 rivets. This is the smallest die that
works well in 0.010" or thicker styrene The .010 die works well in
0.005" styrene or thin brass.
For the large grab irons, I placed a rivet at the
location where the grab iron is to be attached and another 0.030" above
it. I then drill out the bottom rivet. This will be a guide hole for
when I drill the side for the grab iron wire. The top rivet is left to
represent the grab iron mounting. The process of adding the rivets to
the side took about two hours.
July 24, 2004
With the rivets in place, I cut out the side from the sheet. Obviously,
the side of the model can not be 0.010" thick. So i glued the riveted
sheet to 0.020" styrene. I will be making another riveted sheet for the
inside of the gondola so the final combined thickness will be 0.040".
Hopefully I can do a two sided casting that thin! This is a critical
glue, since it is easy for the cement to get onto the surface and ruin
it (which has happened too often). One problem is glue can sometimes
come through the rivet impressions if they have broken though this
usually only happens when using 0.005" sheets. With the front side
glued to the base sheet, I cut the base sheet to
size.
The inside rivet sheet was made using the same process as the outside.
On the inside wall along the top edge and just above the floor I added
a horizontal rivet strip of 0.005" styrene.
July 25-27, 2004
With both the inside and outside rivet sheets glued-up I started to add
the supporting ribs. 
Here
I was lucky enough to
have a rib pattern that was quite usable for this car. I had made a rib
for an H21 open hopper project and though the length was much too long,
for the gondola side
the rivets were in the right position and the bottom profile of the rib
matched the G22 rib fairly well. So I cast up a dozen of the H21 ribs,
cut them to rough length and then filed the top profile to match the
new length. Using the reference marks printed on the styrene, I
position each rib and glued it down to the side using ACC. When I
created the H21 rib i placed a rivet at each possible location along
the rib. On the H21, each rib had different number of rivets. With the
fully riveted ribs in place it was easy to chisel the unwanted rivets
from the resin casting. The same process was followed for the G22 using
the builders photo for rivet placement.
A 0.030x0.100" styrene strip was glued to the top, with the inside
endge flush with the inside of the side.
July 28, 2004
After a little light sanding the master is ready to make a mold. (I use
a 2400 grit foam sanding pad to take the sharp edges off. Both the mold
material and the resin like slightly rounded corners vs. sharp right
angles.)
I
use RTV rubber mold material from Bare
Metal Foil. It is a two part rubber that mixes with a ratio of
1-to-1 (equal parts by volume). So you just measure, mix, and pour. In
mixing I try not to trap air bubbles in the compound. The rubber was
poured over the master that was taped down, using double sided tape, to
the bottom of a cardboard box made to fit. The photo shows the box
opened and the rubber mold removed and turned over to expose the master
still embedded in it. Once the rubber is fully cured I will reassemble
the box around the mold and then pour another layer on top. Before the
second layer is poured a parting agent is applied to the rubber to
assist in separating the two rubber pieces.
July 29,
2004
Well here goes. I poured the second half of the mold and after a couple
of hours the two halves were ready for the resin. I use a two part
resin from Micro-Mark. Like
the mold material the resin is mixed with a 1-to-1 ratio. Once mixed
the resin starts to set up fast, in a mater of seconds. If if a large
casting was hard enough, getting the resin into a large flat space
turned out to be a challenge. I had originally thought of flowing the
resin through three channels at the top of the mold. Because the mold
is so large and the space is thin the resin did not flow to every
portion of the mold cavity. So what I did was to pour the resin into
the open mold and then bring the two halves together. Once together,
clamps were applied until the resin set. Back when the molds were
poured I laid a piece of wood into the top of the rubber, creating a
support for clamping. The following three photos show the casting
process and final outcome.
Two clamps keeping
the mold together. A bit of resin oozing out the top only to add to the
rest of the mess.
Once the resin has
set, the mold is opened to expose the newly created part. This is the
inside wall and the details look fine.
The new part is
removed and cleaned up. It looks good, or at least usable! Rinse and
repeat.
With the hard part over, now its time to make the rest of the car
masters. I figure I will need a master for the end, floor, and
underside frame members.
Continued in Part 2 Ends and floor...
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