Designing The Rear Section Chassis Frame

     The overall concept for the chassis framing is to divide it into three sections, each short enough to fit in the BFB-3000 3D printer working volume.  The overall frame for the prototype is 46.27 ft.  The scale is 1/2" per foot, so the frame model winds up 23.135 inches long.
     The BFB-3000 3D printer working area is 9" x 10-3/4" x 8-1/4".  The frame was sub-divided into three sections of approximately 8" length for the project, Front, Mid and Back.  This blog posting discusses progress in design of the back section.  The front and mid sections are already complete.
     The back section consists basically of two side frame portions, a front cross support that includes the trailing truck pivot and a rear sill section.  Progress for this blog post includes the side frame and front cross support.  The back frame mounts to the mid frame section in a pair of pockets which will be bonded using Cyanoacrylate or superglue suited for bonding ABS plastic.  The trailing truck will be attached to the pivot using a #5 screw.
The overall frame assembly will eventually include the front cross support, rear sill cross support and various other detail components such as the equalizer lever mounts, truck spring mounts and several detail components under the cab area.
The first effort consisted of design of the side members of the frame using the USRA Heavy Mikado plan obtained from the internet.   Extracts from the plan are shown at left.  Using a precision caliper and calculator, various dimensions were extracted from the plan for entry into the Alibre 3D design program.  In order to decipher the plan photos and various other references were studied to provide insight into which lines on the above drawings represented the various parts.  Some guesswork was used as detailed plans of the various component parts were not found on the internet.

   
     The drawing at left is the best estimate of the side frame taken from the drawings and various references.  It is designed at 1/2" = 1' scale in three dimensions.  Not shown on the drawing are the actual model dimensions.  The model component will be 7.5265" long, 0.82298" tall and 0.125" thick.  The design concept is to fabricate both side frame members, front and rear cross supports and perhaps some of the detail elements as one combined assembly on the BFB-3000 3D printer.

The front cross brace consists of a box with the trailing truck pivot at the bottom and a boiler mount detail at the rear.  The boiler mount includes rivet detail.

The drawing at left shows the assembly of the two side frames with the front cross brace in position.  Future work will develop the rear sill cross brace and details that will be located in various places on the back frame assembly.

The next drawing illustrates the location of the back frame to the other two frame assemblies.  Note that the other two include various details that will be built as integrated assemblies.

The last illustration shows the frames with driver wheels and trailing truck in position.  This assembly will not be built as an integrated whole to permit motion of the wheels and truck.  The piston assembly and pilot truck are still to be designed and the set of drive rods as well.