Trailing Truck Frame, Wheels and Axle

    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.

3D Printer Material Feed Problems

    Clear (neutral) PLA plastic fiber had been used to build rafts and supports for many of the preceding runs.  Lately, however, the plastic material exhibited brittleness and broke several times in the extruder head.  Further, it also broke a couple of times in the feed tube.  In the most recent instance it broke several places in the feed tube with small segments separating longer lengths and in a couple of cases with several short segments.  It broke about 6 to 7 times in the overall feed tube while sitting dormant overnight!

    The principle location for the breaks was the curved region above (shown loaded now with black and green ABS).  Several small pieces and a couple of longer segments were located in this area.

  

    The round support feeding the tubes to the extruder heads also had a couple of breaks with both long and short pieces.  In order to remove the broken PLA it was necessary to remove the feed tube from the machine, then break up the remaining longer pieces into short segments and work them out of the tube.

    The tubes progress down to the material spools at the bottom alongside several electrical cable bundles.

    The clear PLA had been located at the rear spool location where the green ABS now resides.
    Perhaps the cooler, drier winter climate here in North Carolina had something to do with this problem, or perhaps it was the fact that the spool was about half empty and therefore the material was curled more tightly.  The PLA is very springy and resists attempts to straighten it by simply snapping in two.  Generally the curled material would feed OK up the tube, but would tend to bend the tube considerably.  As the tube approaches the round cable support feeding the extruder head it is more confined and forces  the material to follow a lessor curve thereby putting stress towards straightening the material.
    As an immediate measure the machine was reloaded with the Green ABS material which is not as satisfactory for raft and supports as it tends to warp and loosen from the platform as will be seen in the next blog.

Trailing Truck Springs

    The first attempt to build trailing truck springs combined the separate spring leaf method with the clamp and post as was done for the locomotive springs.  The difference here is that the trailing truck spring is angled upwards which would not suite the flat build method used for the locomotive springs.  Instead the springs were built on their side but with increased thickness and spacing in an attempt to eliminate the bleed-over from one leaf to the next.  As can be seen in the above photo the spring leaves did bleed into their neighbor occasionally.  Further, the spring clamp and post arrangement did not come out well.

    Another problem with the side build was that the ends of some of the leaves did not print well.

Another view of the bleed over between leaves along with extraneous material running from the top spring at right to the mount post at bottom right.

    Further, some of the short leaves came loose from the raft and support material before completion leading to the tangled mess shown above.

    Above is another view showing the bleed over between adjacent leaves and separation of leaves.

    The spring clamps and post parts were overly fragile and tended to come apart when being removed from the support material.

    The second attempt was to lay the spring leaves down on their bottom which required a angled support structure.  The resulting leaves where rough, distorted and incomplete as shown above.   

    The rough incomplete leaves would fall apart during removal from the support material due to extreme thin spots.

    Although the leaves did not work out, the beefed up spring clamp and post parts are good.

    So back to the drawing board.  The next attempt was to separate the leaves further and make them a bit thicker.  During printing several of the leaves came loose which resulted in a large tangle of ABS material in the middle.  Obviously this would not work,  For this print attempt the short end was on the left side of the printer with the wide leaves toward the middle.   

    Another view of the third attempt showing the leaf separation from the support material, also the breakage of the clamp with very little handling.

    For the fourth attempt the pattern was the same as the third, but rotated so the short leaves were towards machine middle and longer leaves towards the outer edge.  This time the leaves came out good with no appreciable bleed over or extraneous material.  The post and clamp are the same as before and appear equally fragile.  The pattern was not modified to beef those parts up as was done for the second attempt.  
The parts made during the second attempt will be used to assemble the springs and the design pattern changed for any potential future build.

    The above photo was made showing the collection of parts made to iron out the proper method to orient and build the trailing truck spring leaves, clamp and post.  The printed structure at bottom right is the fourth attempt and resulted in usable good parts.

    A second set of fourth attempt parts was then made and is both sets are shown at bottom right.

    The only extra material to be removed consists of some support material and a few small strings of black ABS material between parts when the extruder transitioned between sections.  These will come off easily.

    The first attempt is made in a similar manner as the fourth except two spring sets were made together.  The above photo clearly shows the bleed over between the leaves which were spaced too little.  Also the post structures in the top middle are poorly made being too thin and oriented incorrectly.

    The first attempt parts with back lighting show the significant amount of bleed between parts along with misalignment of extrusion head leading to bridging material.  The left set of springs is aligned for the photo.

    The right set of spring leaves is aligned with the back light in the above photo showing similar interleave bridging of material.

    The first attempt also exhibited poor build of the clamp bottom with posts in the middle and extrusion skips which are caused when the material does not adhere properly.

     The above photo of the ends of the first attempt shows the distortion of the leaves, particularly on the left side set. 
    The selection of part orientation is very critical to printing success.  It has proven repeatedly that several attempts are generally necessary to get the desired results.  With the completion of two sets of usable springs all the parts are now ready to build the back section of the locomotive frame.  However, it will be necessary to also build the trailing truck to check alignment and fit during assembly, so that assembly will be built and assembled next.