3D printing part design

Once the material and the 3D printing technique, therefore the supplier, chosen, we can know exactly the limits of this technique and modify one last time the parts if necessary. Finally, we export the files in STL (stereolithography). In AutoCAD 2000, a parameter is used to adjust the curve smoothing by increasing the fineness of the mesh; this is FACETRES. By default, its value is 0.5. Raising it to its maximum of 10 greatly enhances the appearance while only doubling the file size. So don’t deprive yourself.

Errors in STL files

Attention: the export to STL command can give errors (“holes” in the mesh for example). Typically, 3D print providers correct these errors before printing the objects, but you’d better doing it yourself before sending the files.

Many software programs are able to search for errors and make corrections, but most are commercial. There is an old version of nettfab (from Autodesk), free, that does this job very simply. This is version netfabb-basic 7.4, available on GitHub. A tutorial is available here. You’ll see that it is very simple.


Here are images of STL files obtained with 3D-Tool Free Viewer, a 3D object display utility — really — free which allows you to view STL files (and other formats) and to detect any inconsistencies. It can do much more that will not be very useful to me, but who can do more can do less, and this program is not too cumbersome.

Main parts

  • Legs. The cab-side leg is illustrated here, the most complex, with holes for fixing the ladder, supports for gangways, tenons for assembly with beams and holes for cleaning the printed object (removal of the inner support wax).
  • Double beams (two symmetrical parts), including the trolley rails and the (flat) power cable supports.

Cab-side leg

Double beams

  • Cab (deprived of its floor printed with other parts, see below)


  • Electrical cabinets with their shelter.

Electrical cabinets

Grouping of small parts

Small parts can be grouped in clusters, as in injection molding. I thus grouped:

  • Driving bogies, head to tail so that they are not attached by their fragile part;

Driving bogies

  • Trailing bogies. I hope that the immobilizer brake wheel — supposed to be four spike, I have no explicit photo — will be correctly rendered;

Trailing bogies

  • Cab base, current pickup support, hoists and electrical cabinet infrastructure;

Base, trolleys, hoists

  • Trolleys


The inside of the trolleys, hollow, is provided with holes to attach the hoist cables. I didn’t plan a winch! But it would not be totally unimaginable…

Trolley sectional view

  • Leg beams

Leg beams

Note: after receiving the parts, it turned out that the idea of putting them together in cluster was not good, even for very small ones. Indeed, the fasteners cause traces throughout the wall height, traces due I think to the support material, and that are very difficult to remove.

We see that the design of objects for 3D printing is not very complicated, once the model correctly designed. This is not the same for the photo-etching, as we are going to see now.

Nevertheless, minimum dimensional constraints must be respected: for example, at Shapeways, at least two dimensions must be greater than 2.5 mm; the sum of the three dimensions must be greater than 12 mm. It is sometimes enough to add a detail to get compliant.