The main drivers, axle and bearings have been now built successfully in black ABS along with the intermediate drivers, axle and bearings and the MIDS frame section. The fit of the various parts is good with a suitable slide fit for the bearings in the frame, low rolling friction fit between the bearings and axles and snug fit between the axles and driver hubs.
Now that the MIDS section of the frame is complete the next forward section will be built. The method of frame build is not prototypical it being necessary to subdivide the frame into about 4" sections for the build. The complete frame will be nearly 24" long including the main frame and trailing truck frame portions. The various frame sections feature overlapping joints that will be glued together. On the prototype the trailing truck frame portion is bolted in place on the rear of the main frame. On the model the trailing truck frame portion will be glued in place instead of the many bolts used on the prototype.
To complete the MIDS frame portion, frame keepers will need to be built. The frame keepers span the bottom of the open frame slots that permit the bearings to slide into place from the bottom keeping them in place and strengthening the frame in the process. As on the prototype these will be bolted on to permit disassembly later if need be for modifications or repairs. The frame keeper bolts will likely be 0-80 size machine screws. To accommodate the screws, the frame will be drilled and tapped.
The intermediate driver-axle-bearing assembly is in the foreground while the main driver-axle-bearing assembly is in the background. The mains have the large rod shafts protruding to accept the side, main and eccentric rods while the intermediate rod shaft need to accept only the side rod. The main drivers have had a preliminary cleaning to remove the green support ABS and still need grinding and carving to remove the remaining material before painting and assembly.
The main driver at left sports a much larger counterweight than the intermediate at right. You can readily see the green strip residue of the support material on the inside of the main drivers at left. The intermediate drivers on the right have already been cleaned up by removing all traces of the support material in preparation for painting. The parts above are dry fit and will not be glued until painted. At this moment only painting of those surfaces that were trimmed and ground is anticipated. Depending on how that comes out, the balance of the drivers, bearings and axles may or may not be further painted.
The sizes of the drivers are shown above by including one set of the previously built green ABS drivers used to develop the build and design processes. These will not be used however and new ones in black ABS will be built. At left is the main driver set which has the largest counterweight. The intermediate driver set in the middle features a counterweight that lies between the main and the front/back driver at right. Also, the main driver features a larger axle than the other driver sets as per prototype.
The main driver has the much larger rod shaft while all the other drivers have a small rod shaft. The bearings for the main are larger to accommodate the larger axle diameter while all other axles and bearings are smaller. On the prototype the main axle is 12" diameter while the other driver axles are 10" diameter. Prototype drivers are 63" in diameter over the tire portion with the flange extending about 1". All these dimensions have been successfully reduced to 1/2" per foot, 1/24th scale on the built parts.
The arrangement of the drivers is shown above in order from right to left. The order is Front, Intermediate, Main and Back. New Front and Back driver, axle and bearing sets will be built to complete the driver sets for the model.
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