The cabin basic design, still needs to be rounded on the spiky side edge and smoothed on the top, before proceeding to the fine filing. It is easier to re-build the shape of only the upper part of the cabin inside FreeCAD: with just one simple “fillet” action on the side edge, the basic rounded shape is there.
Smoothing the ridge on the top is a little bit more tricky: applying a fillet to any short edge doesn’t work well, as the segments composing the ridge are oriented in different angles. Then the solution is to cut away the spiky part of the ridge, leaving a smoother surface instead.
I created a profile which was cutting out the ridge, but at the same time including the whole upper cabin. The solid generated revolving it around the longitudinal axis includes the cabin, cutting out just the thin part of the ridge to be removed. The boolean difference of the two shapes does the rest of the job: the result is the original cabin, with a smooth surface instead of the ridge.
This shape is now ready to have the windows cut out, before being exported in stl format to be finely adjusted inside Blender.
The lower valance Lorenzo designed with OpenSCAD shows a significant improvement compared to the original basic model I created with FreeCAD.
Nevertheless it remains too spiky and irregular in the inside profile. Here comes into play my skills as a new Blender user: I had a lot of fun learning the basics of meshes manipulation to adjust, recreate and smoothen it.
Now it’s time to adjust the other profiles to this new refined lower valance and re-create the upper part of the cabin.
As a break during the Class 43 IC125 remake, I’ve been asked by Lorenzo to design some buffers, as an easy 3D exercise, which I was glad to do.
Within one afternoon I came up with the design of the Metropolitan Electric Locomotive BT-H 1907 buffer in 1:87 HO scale.
First I drew the section of the buffer, as a FreeCAD sketch, using lines and circles.
I generated the revolution solid from the section to create the body of the buffer, to which I added the plate with the bolts to attach it to the carriage.
The front part still needs to be cut on top and bottom, to reach the final shape: it’s enough to intersect the complete structure with a cuboid, as long as the buffer section and with the height exactly dimensioned to cut the round part of the buffer, wide enough to include all the buffer body.
Once the buffer is complete, it’s time to create an array of as many as wished (in my case 10). In order to have all them printed there must be a sprue added to the matrix of buffers: then let’s add a support to the single element before creating the bidimensional array.
I already uploaded this model in 1:87 scale on shapeways and am waiting for the prototype in Frosted Extreme Detail. After checking it, I will make it available for sale, also in other scales and materials.
After exploiting all the available features of FreeCAD, facing its limits for my project and getting the first prototype, time has come for the redesign. There are a few changes in the concept (basically how to split the locomotive into parts and which details to provide) and a new workflow, including openSCAD to design 3D solid shapes which are not simple extrusions of 2D faces, while keeping FreeCAD for some easy geometrical sketches, to extrude simple shapes and to put the basic blocks together at the end. Blender is also of great help to work with the mesh format both for some fine adjusting and handling of curved surfaces to be exchanged among different software tools.
As first step we (my model partner Lorenzo and I) decided to split the design of the cabin with a horizontal plane cutting at the level of the spiky edge on the front, just below the lights housing: he wanted to redesign the lower valance with OpenSCAD.
We started again from the drawings with Inkscape, traced over the blueprint and shrunk to the 1:87 scale dimension.
The valance (the lower part of the cabin) required (and openSCAD allowed it 😉 ) more work: Lorenzo recreated the basic solid inside OpenSCAD , then he could create the valance as intersection of ellipsoids, shaped as he needed, matching the section of the upper part: this hand definition of the shapes would not have been possible in FreeCAD.
Finally I received the first 3D printed prototype: the white one. In the pictures it is next to a 1:76 class 43 shell from Lima (the turquoise one) for comparison. Here below you can see the side details I added: the inset for the grid, the window cuts.
The longitudinal cutouts where the roof starts are meant to host the roof grids: either created with photo-etched metal, or the grid blocks to plug in I will print in the next version.
All the roof details are still to be done, while on the back I made the proper shape and the window cuts are done.
I’m already back to work on the “to do” list for the next version. I’ll keep you posted.
To be ready for the window cuts, the cabin needs too be hollow: I designed the profiles for the internal cavity of the cabin, extruded and intersected them to have a solid to be used to cut out the internal room of the cabin.
Then I drew the shapes for all the windows, I created an extrusion solid from them, positioned it close to the part to be pierced and cut it out from the main solid (e.g. from the half cabin). I created in a similar way the frames internal to the openings and fused them together with the newly created pierced solid. This technique worked quite straightforward for all the windows on the cabin, the body and the back.
Then I faced the openings of the body for the grids on the side and on the roof. While the cut was as easy as for the windows, in these cases instead of the frames I added the internal bars supporting the side grids (as in the real case) and created an “L” shape behind the roof grid cuts to allow the final user (the modeler) to position and glue there the metal thin film structure representing the grid.
When uploading this prototype on the webpage of the 3D printing company, the support bars behind the side grids openings didn’t pass the wall thickness checks for the white strong & flexible plastic. Then I added a panel just behind them to make the printout possible. I’m waiting for the sample to be shipped at my own home, probably next week 😀 .