Exporting to STL

STL, which stands for Standard Triangulation Language or Standard Tesselation Language is a file format used by stereolithography software. STL-Files describe the surface of 3-dimensional objects. BURRTOOLS can export single shapes into STL files so that 3D printers can quickly fabricate prototypes of them.

Introduction to 3-D printing

There are two popular forms of 3-D printing: SLS and FDM.

The SLS (ShapeWays and TNO) laser sinters nylon. ShapeWays currently charges by the volume of sintered nylon. SLS pieces are always white.

FDM (Stratasys) charges by the time it takes to make the piece. It has two modes: solid and sparse. Sparse mode is quicker and uses less material. In sparse mode the interior of the pieces are honeycombed.

Having a hollowed piece will be cheaper and quicker for SLS — it will be the same cost and speed for FDM because a hollow piece will still have a support structure inside the hollow, but it will be of a different material. The thing to realize is that with SLS, if there are no holes to the hollow part of the piece, the nylon "sand" will be captured. This should not be a problem except for the weight of the piece. But keep in mind that some printing services will charge you for the surrounded volume as well as the for the actually printed volume.

Exporting

The main menu entry Export - STL opens the window seen in Figure StlExportWindow. The window has a shape selector, a 3-D view of the selected shape and some parameters that control the shapes created. The exact parameters depend on the grid of the current puzzle. The 3-D view displays the shape the same way as it will be exported into the STL file, so you can see what the shape will look like.

On the bottom in the status line you can see what volume the current shape with the current settings has.

In the status line are also two buttons to choose how the shape is displayed. Either normally from the outside. The 2nd view will show you the inside of the shape. This is useful if you print hollow shapes and need to see what the internal void looks like.

Figure: The STL-Export window

Hollow Shapes

There are mainly 2 different exporters. One for the sphere puzzles and one for all other polygon based puzzles.

When creating spheres you can simply create hollow shapes by giving the inner radius a value that is different from zero. The resulting shapes will automatically have a lot of holes that connect the inside and the outside. Those holes will be symmetrically placed and they are in places on the sphere where they normally don't interfere with solving.

For polygon based puzzles things are not that simple. Here a hole at the wrong place could make pieces stop from sliding or get stuck into one another. That is why you can specify where exactly you want the holes. Initially there are no holes at all. By shift-clicking onto faces of voxels you can "drill" a hole through this face. The hole will always be in the centre of the face. Ctrl-clicking on the face will remove the hole again.

Don't forget to first set a proper wall thickness and tube size to actually see the holes.

Parameters

The following parameters control the generated shape and file.

Filename and Path control the name and path of the generated file. Those are common parameters for all grids.

Binary STL: controls whether a binary or a text STL file is created. Normally binary files are the right choice because they are much more compact. But sometimes it might be useful to use the text form. For example when you want to see what is going on in the inside of an STL file, or when your printing service has problems with the binary file.

For polyhedron based grids there are the following parameters that control the shape of the generated pieces

• Unit Size: controls the base length of the created voxels.
• Bevel: controls the size of the bevel
• Offset: allows a gap between the pieces, so that it is actually possible to assemble them. If the shapes were made to correct sizes they would touch, making movement impossible.
• Wall Thickness: controls how thick the wall of material will be that encloses the internal void. When the wall thickness is zero, then the piece will be solid. The piece will be solid as well, when you make the wall too thick.
• Tube size: is the size of the "tubes" that connect the inside void with the outside world. The size is given relative to the size of the shape where the tube is located. So 0 means no holes and 1 means tubes as big as the face that the tube is on. The "tube" is actually a hole of the same shape as the face that it is on. So if you put it onto a square face of a voxel you will get a square hole.
• Leave inside grooves: will, when tagged leave a lot of grooves in the generated shape so that the shape looks like it is glued out of a lot of singe voxels.
• Leave outside groved: will only leave the grooves on the outside of the shape but will fill all the grooves that will actually go through the generated shape. To understand the difference of these 2 options, build a shape out of 2x2x2 cubes and look at the different shapes. Use a bigger bevel and offset to better see the differences.
• Remove grooves in void: controls whether the grooves will be removed from the shape of the inner void. Less grooves will result in less material but more grooves might be a more stable result. So you may need to experiment what the effects of this option are on the printed result.

For spheres the parameters are as follows:

• Sphere radius: controls the gap between the centres of the single spheres. It also is the maximum radius the spheres can have. This value is in output units
• Connection radius: controls the radius of the connection cylinder between the spheres. As the spheres mathematically only touch in one point connectors need to be added. Those connectors are cylinders. The radius of those cylinders can maximally be so that they touch one another. If this value is 1 then the cylinders have their maximal radius, 0 would mean no connection.
• Curvature radius: controls the radius of the transition between sphere surface and cylinder surface. If this value is 0 no transition is done and there will be a bend in the surface. If the value is 1 the maximally possible area will be used to go from sphere surface to cylinder surface. When there is only little or no space for the transition (e.g. when the connection radius is close to 1) there might be a bend, even when this value is close to 1.
• Offset: just like with the other grids this makes the spheres smaller to make the puzzle actually assembable. This is in output units. Keep the values small if you want to have working puzzles. Most puzzles might not even require a value larger than zero. But you can get cool mathematical objects with a bigger offset
• Recursions: controls the number of used triangles to approximate the surfaces. A value one bigger will result in approximately 4 times as many triangles and accordingly smoother surface but also bigger STL files. Don't make it too big as it will result in long calculation times and huge files! Normally a value of 3 or 4 is enough.
• Inner radius: controls the radius of the hole inside the sphere. This radius must be smaller than the sphere radius from above. The difference of these 2 values defines the wall thickness of the sphere. The Offset is applied to both values in the same way so that the wall thickness stays constant.
• Hole diameter: controls the diameter of the hole that connects the void inside the sphere with the outside world. If you leave that value 0 the inside of the sphere will be completely surrounded by the sphere itself and material inside the sphere can not get out. Depending on the printing process that might not be a wise choice.
• Square Hole: the hole from above can be round or square. This is mainly a matter of taste, so make your choice.