The Back Driver Section (BDS) is a bit less than 4" long and took 18hr 36min to print. The significant amount of green ABS support and the need to switch extruders on each of many layers drives the print period. The back end of the BDS section is at the top.
The support material removed in a manner similar to the other frame sections leaving stripes of green ABS attached where the support material came in contact with the black frame. Removal is done with a model knife.
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Once the frame has been cleaned up it is ready for attachment to the other two sections previously assembled. Before assembly the new section is held in place using rubber bands to check fit and dimensions. Small adjustments were made by removing material at the joint to square up and set the driver to driver distance.
During gluing with CA various tools were placed on top to hold the frame solidly on the glass desktop. The ruler shown was used to verify that the frame was straight from front to back. Rubber bands are just visible at the rear holding the new BDS to the rest of the frame. The ruler is 15" long.
After the tools were removed the rubber bands are readily visible. The band and red plastic wedge at the top side in the photo were used to tension the frame with a bit if side pressure to hold it straight aligned to the ruler. You might be able to note that at this point the frame is 12" long. The three sections (MIDS, FDS and BDS) are half of the frame sections that will ultimately be included. This portion contains the four sets of drivers.
The three parts of the frame are each built with integrated sub-parts such as cross braces and the brake hangers. Some of the larger cross parts such as the link supports and boiler mounts will be separately added as they are fairly large and would have made the build of the frame sections unwieldy. A fourth set of drivers is being fabricated to complete the ensemble. Previously the Front, Intermediate and Main driver sets were built and shown. The Back set is the fourth. Once all drivers sets are ready and fitted, the frame will be drilled and tapped for the pedestal binders and they will be attached with screws.
Design effort is underway to complete the frame sections over the trailing truck. Much of that design work was done prior to the BFB-3000 3D printer arriving. It may need to be subdivided into two sections as has been contemplated, although it would just barely fit within the Z height capability of the printer (8 1/4"). The combined Back Frame Assembly is about 8 1/8" long as currently designed. The trailing truck equalizer lever mount needs to be designed. It is located on the frame about half-way between the small mounting bracket at left center and the left front of the frame.
The back frame slides into slots on the main frame and gets bonded in place. The trailing truck rides under this frame section supporting the firebox end of the boiler and cab. Other moving parts also attach to the back frame including the truck spring mounts, springs and equalization lever and rods, and centering spring. The above design assembly does not yet show the equalization lever mount, both equalization rods or the centering spring assembly. Once the back section is added the frame will be about 18" long.
Another part of the frame is located up front, the Pilot and Cylinder Section (PCS) frame. That portion will add about 4" more to the front.
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