The recently built the adjusted axle, intermediate drivers and bearings are shown fitted to the MIDS frame section. The wheels fit snugly to the axle making alignment less of a problem. The bearings fit well on the axle allowing free rotation without binding. The only issue is that the bearings fit too loose in the frame slots allowing excess fore and aft motion which could be a problem with the operation of side rods later. The width of the bearing portion that fits the frame slot will be increased slightly to promote a better fit. The frame dimensioning is correct to the main plans.
All the parts were built with black ABS on a green ABS raft with raised support for the parts. This practice allows relatively easy removal from the raised support rather than the more solid raft which holds so tightly that removal is extremely difficult or impossible. The bearings rotate freely on the axle, the wheels fit snug on the axle. The right hand wheel shows the result of grinding away the remnants of green raised support material using a Dremel tool and drum sanding wheel. The surface is smooth and will be painted with flat black enamel before glue assembly. The drivers are 2.625" diameter over the tires that contact the rails and spaced 2.2135" between inside surfaces. Both of these dimensions are 1/24th of the prototype dimensions on the USRA plan for a heavy Mikado. The rails will be spaced 2.354" (59.7958mm) for a scale 1/24th guage. This is larger than G gauge which is 1.772" (45mm) so a custom section of track will be built to display and test the models moving parts.
The intermediate wheel, axle and bearing set above is partially disassembled with the axle remaining inserted into one wheel. All the above parts have be cleaned up ready for painting with flat black. At this moment only those portions of the parts that were sanded or carved will be painted leaving the original black ABS on the outside of the wheels, portions of the bearings and all the axle except one end that was attached to the ABS support during the build.
The above parts are the main axle and bearing set. The main axle dimensioning was adjusted the same amount as was done for the intermediate axle and came out almost exact on scale dimension. The Front, Intermediate and Back axles are identical to one another and have a prototype dimension of 10" while the main axle has a 12" diameter. The bearings for the main are correspondingly larger to accommodate the larger axle. The bearings came out a bit too large on the width that comes in contact with the frame slot, so that dimension will be reduced a bit and the parts re-built. The green ABS support structure has been removed from the parts but small residue remains to be cut or sanded away as they will not simply pull away as the majority did. The main driver wheel designs are complete awaiting their turn on the printer for build. Their axle hole ID has been adjusted by the same amount as has been done for the Front, Intermediate and Back drivers which should cause them to fit snug on the main axle.
The clam-shell holding fixture above was built to hold the axles for the Front, Intermediate and Back drivers, provide a space to contain the bearings during the assembly process and precisely gauge the wheels during gluing. This fixture has been used to assemble several of the earlier build attempts to verify the process. Another similar fixture for the main axle, bearings and drivers will be built with all dimensions the same except for the half-round end holes in the middle to accommodate the larger main axle.
The axle with bearings mounted is installed in the half round apertures at the ends. The wheels are shown in rough assembly above to illustrate the scheme. Then the clam-shell is closed and held snug with rubber bands.
The rubber band around the clam-shell keeps the axle and bearings in place provided the pressure to remove a wheel for gluing is not excessive. Each wheel is removed and a small amount of Cynoacryalate (CA) applied near the outer end of the axle and the wheel carefully installed with the axle end flush with the surface of the wheel center rod crank. Then the process is repeated on the other wheel. After gluing both wheels additional rubber bands are applied to hold the wheels firmly to the fixture while the CA cures.
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