Previously the trailing truck axle and two wheels were fabricated using clear PLA raft and supports. One wheel was built back down and the axle built on end standing vertical. After grappling with the tendency of the clear PLA to break in the feed tubes, green ABS was substituted to build raft and supports. Two wheels are shown above, one still on the raft and support base.
The engineer side of the trailing truck frame was then built using the green ABS raft and support. During this printing fairly long runs of ABS were placed by the G-Code software which tended to lift off the platform as the build got thicker. The end where the pivot pin is located at right lifted considerably and touched the extruder heads which pushed it down and somewhat sideways as it progressed. In an attempt to fix this issue, Scotch tape was applied as shown to partially hold the tip down and keep it from contact with the extrude heads. This only worked partially and several added tape applications were necessary as the build got thicker.
The photo above shows that the right and left ends of the build lifted from the build table. The right end lifted almost along it's entire length from the black journal box at middle left. The left end lifted but did not interfere with the extrude heads.
After removal from the printer the overall thickness of the build is noticeable with many layers of green ABS support structure filling in below the frame. This is due to the fact that the axle journal box was close to the bottom of the build and forced the majority of the frame to be elevated above the build platform by about 3/8".
The pivot mount above is located above a jumbled mess of green support material. This came about as the head kept contacting the green material even though it was held down partially with tape. The layers obviously delaminated.
The frame is a long and slender U beam configuration which required support on the bottom and top.
The journal box for the axle serves as the bearing for the axle and connects the front and rear U beams. The bottom of the journal will be build separately and glued in place. The axle will fit into the journal from the inside. The two halves of the frame are to be bolted together at front and rear so that the axle and wheel assembly can be removed if needed.
The ouside of the journal is closed and the axle is contained between the outer walls of the two journals keeping the wheels centered. You can make out rivet detail where the journal casting is connected to the U channel frames.
The U channels are filled with support material to permit build of the bottom and tops of the channel.
The truck pivot mount is not well supported as shown by the delaminated support material above.
The wheels built on PLA and ABS exhibited flange distortion. This was attributed to the warpage induced by the relatively long raft and supports below the wheel.
Even the wheel built on PLA had some flange distortion, but not as severe as the previous wheel built on ABS.
The raft and support was thinned to minimal dimension which resulted in almost no visible distortion of the wheel.
The next series of photos will show removal of the supports from the axle previously built. The part looks like a miniature skyscraper with the black axle up the middle of the clear PLA support material.
Thin sections of PLA were on two sides with very thick supports on the other two.
Some of the supports were quite easily removed by hand.
The remaining support material was easily removed using a small pliers, twisting the support material relative to the black part.
The earlier distorted wheel built on ABS and a second built on the thinned support are shown above. The thicker support removed readily from the wheel leaving very little residue. It is another story with the thinned raft and support however.
The thinner raft and support proved to be hard to remove, simple bending pressure did not release the support from the wheel.
Using pliers and finger pressure the wheel was eventually separated from the bulk of the support, but nearly half the wheel still had material that was attached very strongly.
Using a model knife and needle nose pliers most of the material was removed to the point where a sanding wheel will finish the job as is shown below.
All wheels fit the axle quite well with little wobble or looseness. The ends of the axle will go into the journal boxes which are outside bearings for the trailing truck. The wheel at right still needs sanding to remove remaining residue.
With both wheels on the axle a quick fit check shows that the gauge is nearly correct. With undistorted wheels it will not require any design adjustment of the parts.
A fit check of the axles and wheel into the journal also shows good fit with little slop. Once the frame is removed from the support the wheels will fit well.
Next item on the agenda is to remove the raft and support material from the engineer side truck frame. As can be seen above many layers were layed down to support the frame above the platform. At the truck pivot end the delamination is severe.
The first effort was to remove support material around the journal. A needle nose pliers is the main tool used to remove truck frame support material.
After removal of some of the internal support of the rear U frame the shape can be seen.
The many layers of support requires care and planning in order to remove the material without damaging the frame part.
After several steps the journal and rear U frame are clear. Some support residue will still need removal by sanding with the Dremel tool later.
After the bulk of the support has been removed bits of support residue are removed using a model knife. Residue on the outside is to be removed using the Dremel tool with sanding wheel. Inside support material is removed using a model knife.
After removal around the pivot it is apparent that the pivot is distorted downward clearly showing the distortion of the part. More than likely the part will not be usable unless the pivot part is removed and replaced by gluing a replacement in the correct location. Such an action would require cutting and grinding away the defective portion and separately building up a replacement on the 3D printer.
Another view of the badly distorted pivot with considerable excess support material still in place. The excess material hides much of the damage.
Initial fit check assembly shows the downward tilt of the pivot at right. The rest of the frame half is quite good. Since the frame takes so long to print perhaps an attempt to build a replacement pivot portion of the frame will be done.
In the above photo the trailing truck engineer side frame is fit to the wheel assembly and placed under the rear frame. At the front on left the pivot mount is wedged in place temporarily to show the approximate location of the truck.
Above is the pile of removed support material which in volume is more than the truck frame half.
Finally another view of the truck frame half shows the distinctive downward tilt of the pivot plus the bent frame caused by the release of the support material from the build platform.
Frustration with distortion caused by the difficulties with warpage of ABS parts built on the 3D printer point out that this method of additive part build has significant issues. Perhaps a heated platform is needed to reduce or minimize the distortion brought about by adding hot material to cold with the attendant shrinkage causing the part to bend. As a result, a set of miniature sized machine tools are being acquired to enable rework of parts when necessary and perhaps to build more of the overall model. The limitations of Fused Deposition Modelling has made certain parts very difficult to build.
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