Hi guys. This is a two part post because of the number of images. This part concerns the design, while the second part will be about the building of a Megamorphix. I just thought that you may be interested in the entire process of puzzle building the way I do it.
Inspired by this post
and the release of the Witeden mini 4x4x4
(11.5mm cubies) I decided to make a Megamorphix. I don't think that I have the building skills to make one from plastic sheet (and it would be very tricky because of the small cubie size) so I of course used Google SketchUp to design the extensions.
First, create a cube of edge length 11.5m. Yes, that is meters. I do the design 1000x full size to avoid some nasty quirks SU has when it tries to create very small triangles. The scaling is taken care of during the transfer to Shapeways.
Megamorphix 000.png [ 98.65 KiB | Viewed 1843 times ]
Next, duplicate the cubie to make a 4x4x4.
Megamorphix 001.png [ 159.98 KiB | Viewed 1843 times ]
Now, I define where the turning planes of the cube are, which are then going to be used to create the extension pieces.
Megamorphix 002.png [ 137.45 KiB | Viewed 1843 times ]
In this build I will have to truncate the 4x4x4 across the corner cubies as shown.
Megamorphix 003.png [ 152.33 KiB | Viewed 1843 times ]
This shows the required truncation. The center triangle forms the center piece on the four faces of the final puzzle.
Megamorphix 004.png [ 155.17 KiB | Viewed 1843 times ]
Using the truncated faces, I add guides which will intersect at the corners of the required tetrahedral shape. As you can see, sorting which intersections I need can be a bit awkward, but once you find one edge the rest follow easily.
Megamorphix 005.png [ 157 KiB | Viewed 1843 times ]
The finished tetrahedron, with the outline of the truncated cube shown inside.
Megamorphix 007.png [ 133.15 KiB | Viewed 1843 times ]
Now I add the turning planes of the 4x4x4, which will become the cutting planes through the tetrahedron, to form the extensions required.
Megamorphix 008.png [ 136.26 KiB | Viewed 1843 times ]
Using the planes, I cut out and isolate the extension pieces needed. In the Megamorphix, five different pieces are required. This is the large corner part (4 needed).
Megamorphix 009.png [ 95.88 KiB | Viewed 1843 times ]
Now I have to subtract the part of the cubie to which this piece will be attached, using the cubies I drew before.
Megamorphix 010.png [ 87.75 KiB | Viewed 1843 times ]
Now, this is where SU shows its weaknesses when compare to programs like Solidworks. I need to create a thin shell (I use 1mm thick) to minimise the costs of Shapeways printing. SU has no native shell tool, but you can download free Ruby plugins which add this functionality. They usually work OK on simple shapes like this, but can go horribly wrong on more complex ones. The image below shows a wireframe view of the shelled shape.
Megamorphix 011.png [ 124.33 KiB | Viewed 1843 times ]
I now add fillets. Again, this has to be done using a plugin, and works well for this sort of shape. But again, it can be more difficult for complex solids, which may need a lot of manual work to tidy them up.
Megamorphix 012.png [ 181.34 KiB | Viewed 1843 times ]
Here I have added some small holes which connect the inner and outer "shells" of the part together. These make a manifold object and allow Shapeways to extract the unused nylon powder which would otherwise be trapped inside. At this point the part should be watertight and manifold. I use a plugin called SolidInspector to check this.
Megamorphix 013.png [ 192.48 KiB | Viewed 1843 times ]
This is then exported to an stl file using yet another free plugin. I can now load the stl file into netfabb basic to check that everything is OK.
Megamorphix 015.png [ 53.85 KiB | Viewed 1843 times ]
The next part can be very frustrating. In order to get Shapeways discount, the model density must be greater than 10%. So, sometimes I have to carefully arrange the parts to maximise the packing to achieve this. As you may notice from the image below, I added the yellow sticker template to the design, which added material to the model without increasing the overall size, thus bringing the density over 10%.
Megamorphix 016.png [ 213.27 KiB | Viewed 1843 times ]
Now, export the whole thing to an stl file, check it again using netfabb and upload it to Shapeways (remembering to specify the units as mm!).
In part 2, I will show some pictures of the build process using the printed parts and the Witeden cube.