This post is a miscellany of ‘lessons learned’ on my journey to incorporate 3D printing into my railway modelling work-flow
Removing window in-fill
All the carriages I’ve printed so far have an amount of supportive in-fill within the various window apertures. This has proved surprisingly difficult to remove since, although the infill is very thin, it clings very tenaciously to the edges of the window opening. I tried several tools, including small cutting tweezers, wax-carving chisels, and needle files but, eventually, I had the greatest success with a blade from the Modelcraft Precision Saw Set (0.24mm)
Clearing in-fill from window openings
The Modelcraft set includes 6 very fine saw blades (0.24mm thickness). intended for intricate sawing and cutting in plastics, wood, and photo etched parts. These blades fit onto scalpel handles.
Unlike scalpel blades which readily break, if used for sawing actions, these blades are flexible and can be used both to stab into the thin plastic film and then to work around all the edges of the window frame. In some cases, some of the infill was found to have folded back against the inside wall of the carriage and, in such cases, a small wax-carving chisel was a good removal tool
Printer Bed Adjustment
In my last post, I described problems that I had with adhesion of my models to the bed of my Geeetech E180 printer. I am pleased to have discovered for myself how important the process of setting up the alignment of the bed is, to achieving successful results. Now that I have attended to this detail, my prints have been very consistent and, while remaining firmly in position during printing, have been removable from the bed without ripping up the blue masking tape.
The improvement in reliability has done a lot to raise my confidence in the 3D printing process as being one that can produce good results with very little user input being required, after the initial computer model has been drawn.
After an adhesion failure, which resulted in a distorted carriage body, as described in my previous post, I simply re-inserted the same gcode file into the carefully set-up printer and pressed the ‘print’ button. All went well and about 5 hours later, I had a non-distorted carriage, with no intervention being needed on my part.
I was surprised to see that, when I placed the two carriage bodies side by side, many of the printing blemishes were in exactly the same places on both. I had thought that these were random errors due, perhaps, to backlash in the mechanisms or other mechanical tolerances but, instead, it looks as though they are systematic defects arising from the way the print head tries to follow the instructions provided by the ‘layer’ model from the slicer software.
Comparison of two successive prints
I decided to do some more experiments, to see whether my 3D Printer could produce a reasonable curved roof for my carriages. My initial thought had been to use a rectangle of plasticard, moulded to shape by judicious application of a little heat, as described in a previous post , when I built other carriages.
The possibility of using the 3D printer, however, was too strong for me to resist, so I had a go with the simplest structure I could devise. I sketched a pair of arcs, using the Fusion 360 software and then extruded the sketch by means of the ‘push-pull’ command, to form a 1mm thick single-curvature roof. I added some rectangles close to the edges of the under-side, to form a ‘base from which the roof could be ‘grown’. It was an experiment, since I was fully aware that the raised part along the centre of the roof would have no underlying material and would be dependent on support from the adjacent strips, as the printing progressed.
Sketching the Roof Profile in Fusion 360 software
In the event, I thought that the result was surprisingly good – while not perfectly smooth, the curved upper surface showed only very light grooving. On the other hand, because it started with all the edges lying on the printer bed, there were no alignment features to locate the roof into its correct position over the body.
Printed Roof - Surface Finish
Adding location lugs to a roof
My next step was to add some vertical 'lugs' running downwards from near each end of the roof, placed so as to engage with the inside faces of the end walls of the carriage.
This introduced the problem that the edges of the roof itself could no longer be in direct contact with the printer bed, so I selected the options in the Cura software to add support structures, where necessary. I used the default ‘zig-zag’ support style and allowed the print to take its course.
Zig-zag Support Structure Underneath the Roof
I was somewhat surprised to see how ‘dense’ the resulting support mesh appeared to be, at least at first glance. In fact, the ‘cellular’ structure only applied to the very first layer, in contact with the bed, and subsequent levels of the structure were a zig-zag pattern of very thin walls, rising throughout the structure. This support structure proved much easier to cut through with a knife-blade than I had expected, although it did leave lots of strips of thin material, on which I used a wax-carving chisel, to slice them away from the underside of the roof.
Removing Support In-fill
‘Soldering’ with PLA filament
In chiselling away these support structures, I inadvertently broke off one of the lugs that I had designed to hold the roof in position on the body. At this stage, I tried another technique that I had seen described on the web
This is the somewhat surprising technique of ‘soldering’ the PLA plastic. By setting my soldering iron, fitted with a small conical tip, to a temperature of 200°C, it melts the PLA in exactly the same way as does the print head itself.
By running the hot tip of the iron along the damaged joint, the plastic readily melted and welded together the two sides of the joint, to form a strong bond. Larger repairs can be made by introducing additional PLA filament, in much the same manner as one would use a solder fillet!
Using Soldering Iron for Seam Weld
This made me realise that more complex structures could potentially be assembled from 3D printed parts by using a soldering-iron in much the same way as one would when assembling an etched-brass kit. I think this method of assembly could open up a whole new realm of possibilities.
Finishing the Roof
Although the surface finish of my 3D-printed roof was better than I had anticipated, it was far from perfect. To overcome the slight 'grooving' and achieve a smooth surface, I applied a film of self-adhesive vinyl to the 3D printed surface, which completely masked all the small ‘steps’ produced by the layered printing process. The final roof (sprayed with grey primer) is shown below, on my (unfinished) Composite carriage body and chassis.
Vinyl-Covered Printed Roof
The same methods could be used for more complex roof shapes and I plan to re-visit the clerestory roofs that I fabricated for some of my previous models. It should also be possible to add features, such as oil lamp housings, as part of the 3D print.