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Last month, I had cemented all of the inner frames to the top horizontal girders, then notched those and bent them downward at the inland (or “furnace”) end. Shortly after that, I soldered together the bottom braces that support the tramway:
Now I was able to permanently attach the bottom [inner and outer] horizontal girders, which I did. At this point I was ready to try the ‘acid test’ – seeing if the existing brass material was strong enough the support 2-3 lbs of hanging weight in the exact center. I tied half of a brick to my daughter’s shoelace and tied it around the bottom girders, and here is the result of that experiment:
It appears to me that the bridge will support an HO scale motorized tram and brass clamshell bucket when I decide to add them.
The next challenge was to attach a pair of rails to the center bottom horizontal girders, for the tram. I dreaded the thought of trying to cement each individual rail on either side while ensuring that the two stayed perfectly parallel, so I started with something guaranteed to be properly spaced – a 36-inch section of flex track surrounded by 1/4” angle girders of identical length:
ob_model_flextrak_braces01.jpg
The angle girders would fit flush against the ties; to ensure that the rails would remain perfectly straight, I used two aluminum angle rods to support the rail subassembly….:
…holding everything together with clamps:
Mixing up a liberal amount of J-B Weld, I poured this into the cavity between the rail and the brass L-girder on either side, making sure that the outer ends of the plastic ties were completely covered. The following image shows a cross-section of a piece of the rail subassembly after it was cut off:
Notice how the outside edge of each rail is bonded to the J-B Weld, which is bonded on the opposite side to the angle girder.
The end product after removing the supporting aluminum L-rods was a 3-foot section of brass-encased track….
…which slides right into the inner bottom L girders on the bridge:
All that remains is to solder the track girders securely to the bridge girders, then cut-away the plastic ties from the center – this will be done later.
Shortly after performing the above steps, I saw another photograph of a lake-front ore bridge where the inside braces were visible, and my reaction was about the same as with somebody who has a mild toothache and hopes it will just go away, but ultimately has to get a root canal. The ‘root canal’ equivalent for me was having to rip out all of the ‘X’ braces in the taller vertical frames and replace them with ‘X-W’ configurations:
This resulted in a 1-week delay on the ore bridge project. I placed an additional 5/32” channel piece horizontally across each frame…:
… but replaced the original brass diagonal braces with .125”-square strip styrene on the ‘X’s and ‘W’s. The styrene fit snugly into the open channel sides of the frames, and the gusset plates – also made of styrene – bonded easily to the new diagonals. I made extensive use of the Chopper to get the appropriate shapes:
Here is a view of the bridge after the correct inner brace configurations were installed:
Now I was ready to complete the drawbridge-like extension for the waterfront end of the bridge. Aside from being only ten inches in length and half the height of the main structure, the construction methods were the same, so I’ll only show two photos of the intermediate assembly process:
Before permanently attaching the track sections to the bridges, I soldered some electrical wires to each rail so that I could use a powered tram/bucket hoist in the future, should I desire one. Then I soldered the L girders of the tracks onto the inside L girders on each bridge and cut away the centers of the ties. I did this by first using my Dremel cutting wheel to grind a gap in the center of each tie, then using rail nippers to clip the leftover tie pieces from each side. Why the center gap? Because without it, the pinching motion of the rail nippers will exert outward pressure on the opposing rails (probably harmless, but I didn’t want to risk any more glitches).
Here are three images of the semi-completed bridge assemblies viewed at different angles:
My next planned operation is to install the connecting hinges between the main bridge and the retractable extension. I’ll post those photos when ready. –KJL
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