The trailing truck spring rear mount failed to build correctly as described in the previous blog posting. The mount was rotated to place the top vertical which also put most of the plates making up the part vertical as well. The above photo shows the part at removal from the BFB-3000 3D printer still attached and embedded in the clear PLA support material.
After removal of the support the part came out well with no separation of any of the plates by support material. No design change was otherwise made.
The trailing truck spring rear mount is shown placed on the back frame section for fit check. The part fits correctly on the frame in the approximate location where it will eventually be glued.
Another part being worked this past period is the Hodges trailing truck centering device. This part consists of a tube containing a coil spring with a cone protruding out each end. The cones are held separated by the coil spring up against the outer flange of the tube. The tube was made in two parts with the cones integrated inside, but not in contact.
The parts above are the preliminary build to check the cone and tube dimensions and fit. The cones could sometimes slip out the flange end and the joint between the tubes was too tight.
The cones accept a rod coming from a bracket on each side of the trailing truck. When the truck tries to swing off center the spring applies centering pressure to return the truck. In the center the spring forces on both brackets are limited due to the cones reaching the flange end of the tube.
A coil spring was designed and four copies made as shown above. The spring is 0.08" wire thickness with a coil diameter of about 1/4" and length of 1".
It took considerable patience to remove the support material which virtually surrounded the spring wire including inside the spring. The two springs shown removed work as springs and return to at rest length after being compressed fully.
Another set of tubes was fabricated correcting the fit of the cones and tubes.
The tubes fit together better and the spring fits inside and works correctly. The details for the tube are incomplete with the mounting brackets missing.
The details were added to the tube design. The support structure is shown after removal from the printer. The details required much more support material than was required for the basic tubes.
After clean up the detailed centering device parts are shown above prior to assembly.
The above photo shows the partially assembled centering device.
the fully assembled centering device above will be attached at the bottom of the rear firebox mount between the brackets on the trailing truck frame. Small bolts will be used to provide push rods into the cones. You can see bolt details on the mounting brackets of the centering device tubes.
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