Efforts during the past months have now culminated in fit check assembly of the central driver portions of the frame to the driver sets. The above 3D CAD illustration shows a top view of an assembly of the various drawings used to fabricate the parts as they should appear when assembled.
The three central frame sections (FDS, MIDS and BDS) are glued together while all other parts have sliding fits permitting rotation of the drivers within their bearings and sliding of the bearings up and down in their frame slots. The bears are retained by the pedestal binders which are screwed in position.
The last part to be fabricated was the Back Driver Set. The set consists of the two drivers, the bearings, the axle and the pedestal binders. Each of the parts above was separately fabricated in the BFB-3000 printer. The longest run time was for each driver at some 3hr+ each. The green ABS is the raft and support material for the parts which are fabricated in black ABS. The green supports must be removed before the driver set can be used.
The first step consisted of using a needle nose pliers or hands to pull away the majority of the support material. Residue of the support ABS are stripes that adhere to portions of the parts.
The second step is to further remove portions of the stripes that are suspended between portions of the parts, particularly the drivers. That removal is done using a needle nose pliers. Some cutting with the model knife was also used to trim portions where feasible. The result still leaves attached residue segments of green ABS.
The stripes of green support material tend to form small ridges on the black part. Some can be cut away, but that has proven very time consuming and not easily done. The residue strips of support adhere tightly to the black part material.
The final steps of residue removal is grinding away using a Dremel sanding wheel. That proceeds smoothly although the tool must be used carefully as the plastic is easily ground away excessively. The final result of part clean up is shown above.
The Back Driver Set is assembled above. The bearings are slide unto the axle after installing one driver. The bearings have an outside and inside that differ. The two pedestal binders will be installed after the driver set is installed in the frame.
The above photo shows a collection of the parts that form the central driver portion of the frame and the driver sets.
The first step in assembly is to place the frame on it's back and slide the bearings of each driver set into their respective slots. The set of pedestal binders is shown with 1-72 temporary screws in place ready to install on the frame.
The next step is to screw the pedestal binders in place. All are the same except those for the Main Driver which are slightly longer to provide space for the larger main axle. The screws used here are self threaded in place for now. They are undersized #1-72 screws. The frame will be drilled and tapped later for #2-56 screws.
The fit check assembly of the drivers and frame is shown above. The drivers turn freely and the bearings slide up and down in the frame slots freely. The black ABS parts will receive touch-up flat black paint to hide remaining sanding and cutting marks later.
At this point the central driver portion of the chassis has been completed except for paint touch-up and appropriate threading for the final attachment screws. There remains both front and rear portions of the frame to build and fit. The front portion is the Pilot-Cylinder Section (PCS) that will mount the cylinder block, front platform and cow catcher and ride over the pilot truck. The back portion will be possibly one or two sections that mount the firebox and cab and ride over the trailing truck.
Other parts associated with mounting the valve gear and boiler will be glued to the chassis frame later as well. Along with the side rods and valve gear many, many parts remain to be added to the portion completed so far. Of course later the boiler and cab assemblies will be added as well. These too will need to fabricated in sections to remain within the working volume of the 3D printer.
No comments:
Post a Comment