Making Our Own Molds
We started with the downtown marketplace. We progressed to a railroad company house. Now we're designing our own mold patterns. Each has been a learning experience, to say the least! But we have learned from everything so far. For example, one continuous pattern sheet is better than two or more. The seams will show.
Another lesson learned is pattern sheets are only good for modelling that pattern. If there are any deviations or disruptions, voids in the casting must be created using insets and details added later. That's certainly not a show stopper, but when the pattern sheet itself isn't available or the pattern is more intricate, custom molds are needed.
One example that comes to mind is a cut stone pattern. Concrete block pattern sheets are available, but we're talking about the big, 1'x2'x3' blocks used by railroads for retaining walls and culvert arches. There are no pattern sheets available for them. Another good example is the Grand Hotel and its 3D printed walls, corners, and column details.
The Grand Hotel was printed in positive relief, so to speak. That is to say the bricks protruded and the mortar lines receeded into the bricks, like in real life. To cast those walls we would need a mold printed in negative relief, with the mortar lines protruding from the bricks to create a recess in the casting and portray them correctly.
Our latest attempt at casting is actually casting concrete, not concrete patch, into roadbed bricks. We've replaced so many rotted stringers, only to have the replacements rot away as well, that it's time to replace them with something more durable. Concrete fits the bill. We tried setting forms in the ground then shaping the profile. The results were disappointing.
Enter the idea of casting individual concrete "bricks" with a groomed ballast profile and "trough" to fit the track within. The bricks will have angled ends to allow making curves or tangent sections, depending on placement. These molds are really heavy duty compared to the concrete patch wall sections, made from 8' lengths of wood.
3D printed components that fit in the bottom of the wooden form provide the ballast profile and track slot shape. The design was really meant for 10', not 8' lengths, so an 80# bag of concrete mix has some waste left over. We reconfigured the forms into two 4' long sections, adding a third for a total of 12'. That way we run out of concrete, not forms.
We had three successful roadbed brick runs, albeit the first one being only marginally successful. That's as far as it's gone. The new 4' long mold configuration remains untried. We'll get there, but until there's a mold design for switches and other junctions, we're kind of stuck with just the long stretches of track between them.
Shifting gears back to concrete patch casting, with an emphasis on the cut stone sections for elevated stretches of track and the station siding, would be the best way to get back to running trains again. Those are the areas most in need of remediation and repair. The curves under the golden rain tree are the most problematic raised sections.
The stringers in that curve have already been replaced and repaired once. We removed the track on outer curve after the dogs managed to knock it loose from the stringer, still in good shape. The repaired section of the inner curve is still in fair shape, but the rest rotted and destroyed by the dogs. We removed that track section, just hanging there, an accident waiting to happen.
The station siding is nearly detroyed as well. The stringer has long since rotted away and there's nothing left to hold the track in place. At least the plastic pipe posts are still there. As an experiment, one of the casting mockup sections was placed under an unsupported part of the track but the Florida sun soon baked it into a misshapen mess.
The idea of the mockups was to help visualize the process of joining multiple cast pieces together into a single, elevated platform with the cut stone walls and arched culverts on either side. But that means somehow providing a slot for the track along with some means of keeping those cast pieces and sections together and in place.
The idea is to use the cast sections as part of a form to pour concrete in to hold everything in place. The next step is to make that happen. This page will be updated as progress is made.