General design

Now that the scanning works, it’s time to explain the design of the tool. The size of the finished system of course makes it impossible to print it with any current 3D printer available to me, but even with MiniFactory’s 15 x 15 cm build table, it is doable. I wanted to have a 30 cm diameter turntable, and a 60 cm diameter frame base so as to have space to shoot objects bigger than 15 x 15 x 15 cm. The turntable is printed in 12 parts, assembled with screws, just like the arcs. I didn’t want to use glue, even if ABS is easy to build with glue. There are a couple of other parts too, like the cup below the turntable on which it revolves, and the three vertical arc mounts. There is a small triangular part at the top to assist in fixing the top arcs together, and that is done with a bundle strap. It’s easier than using screws and works just as well.

I modeled all parts in Blender, exported to STL and printed on my three Minifactories. I wanted to keep the design as simple as possible, and recycle parts so as not to have to change the printing setup every time a part was finished. Therefore the base arc and the three vertical arcs are of the same parts, and as ABS flexes a little, the whole setup can be put together and held in position by a single bundle strap at the top of the arcs. Let’s see the parts in detail.

Base arc

The base arc is 60 cm in diameter. I designed it starting from a 60 cm diameter circle, with 72 vertices. This is twice the number of degrees in a circle, giving me six parts of 30 degree arcs for the base. It was only after I had printed a couple of the base arcs that it occurred to me it might be a good idea to print the rest with a raised center, so as to have a place to mount the central vertical arc, and to have the other top arcs approaching the center arc not from right angles, but slightly over 90 degrees. Therefore I edited the base arc STL file to have a vertical stub on which I merely pressed the vertical arc mounts

The arc was easiest to design with a full circle. The radius was 30cm, and I set the vertex count at 72. This way it’d be easy to craft three parts per 90 degrees of the arc. The full circle is then copied three times and scaled back one centimeter, visually, because accuracy isn’t the key factor here.

Of this I selected ten vertices of all four circles, then pressed Ctrl+I to invert the selection. The vertices now selected can be discarded, to leave you with the 1/12th arcs:

Now it’s possible to use the Bridge option in LoopTools and add faces between the relevant arcs. Also, at this point, I will add edge loops at the ends and in the middle part, to come up with this layout.

This can then be extruded up 3mm as a whole, and then with just some faces selected, be extruded 5mm more for the ends, and 10mm for the middle connector:

And as always, at this point I realized it’d be much easier to join the arcs together if there were a trench in the ends for a screw, but I had not designed one. This is again a case for edge loops. All you do is insert one (Ctrl+R), then push the mouse wheel for as many loops as you need, and hit Enter. Using the mouse for confirmation is not the best idea, as you can then easily move the loops off kilter. Then just take out the faces you don’t need, and build the missing faces into the trenches by selecting two suitable edges and hitting F:

When you have taken out the faces you don’t need, you need to remember to rebuild all holes so that the piece remains manifold, ie. it doesn’t have any edges not connected to other edges. If you do pure 3D, it doesn’t matter that much, but when you intend to print, it is paramount. The netFabb service will of course fix all such holes, but you have better control over the final fixed product if you don’t send out stuff with gaping holes. Here we are fixing the middle part:

If you were now just to select the two long vertical edges and hit F, you would get a face all right, but it’d violate the manifold requirement:

The orphan vertex would cause this piece to be non-manifold, and without netFabb, the 3D printing software RepetierHost would not start the work. Therefore, to do this properly, you first add a face at the bottom of the trough. add an edge loop, and then add the faces between top and bottom:

And this way, you get the final piece, which can be printed in just 45 minutes. When you get four parts in three hours, it’s easy to calculate the whole arc, and the almost-identical pieces of the vertical arcs, will take you 12 hours to print. Yowza!

The only difference in the vertical parts is that there are two parts without end connectors. These are the ones that are inserted into the fitting that is printed to fit on the middle part of the connectors, and also meet at the top of the arc. This is the fitting for the vertical arcs:

The next part of the blog will take you through the turntable part of the project. Here’s a teaser image from Part 2/3:

It’ll be some time before I get to that part, but after that, it’s all done for the 3D printing parts. Then we can discuss the camera arrangements and other such niceties.