There are a few limitations, as well as a few things to keep in mind when 3d printing an object. If you've printed before, or have a good knowledge of how it works then you can probably skip these notes and move on to the mechanics of the watch. Otherwise, it is important to know how to make an object ready for printing and the options available.Types of Printers
There are two main different types of 3d printers; FDM (Fused Deposition Modelling) and STL (Stereolithography). These names sound overly complicated, but they're basically; Melted plastic printed in lines, and liquid resin solidified by a laser. As you can imagine, lasers are far more accurate than a nozzle head extruding plastic, so Stereolithography printers are far better, and as a result, far more expensive. These are generally professional standard, so for home printing then you'd want a FDM, like the MakerBot Replicator 2
. However, if you really really want an STL, MIT researchers have developed a small relatively cheap one called the Form 1
. Now when I say relatively cheap, it is still about twice the price of the MakerBot, and with a smaller print bed, so keep that in mind if you're picking your own printer.3D Printing Companies and Materials
Never fear however, there are plenty of online options for ordering 3d prints of your own designs (And even sites where you can download other peoples creations for 3d printing, like Thingiverse
). Companies like Shapeways
offer a range of materials that you can print your designs in too, which gives you much more control over the final look than printing something from home. It is important to note the specifications of the material
you want to use though. Due to the nature of 3d printing, every material will have a minimum thickness and minimum detail it can print. Always check for the limitations before designing something in that material or you may lose important detail. With something as small as our pocket watch, we need as much detail to be kept as possible, so the High Detail Stainless Steel
from i.materialise would be ideal, with a minimum detail of .1mm!Sending Objects to Print
As for sending a file to print, there are a few important things to keep in mind. For those unfamiliar with 3d programs, objects are made using vertices, edges and polygons (Though they may be given different names depending on the program). Vertices are the points, edges connect them, and polygons are the surfaces that fill in between the edges. However,
polygons can be deceptive. While in 3d they may look smooth and correct, in reality they may be trying to connect impossible shapes. Here are some key things to look out for (With further explanations below):
Polygons and smoothing
- Objects will be divided into triangles for printing, so make sure surfaces have enough detail, and are made of all quadrangles or triangles.
- Smoothing will not be printed, make sure objects are set to hard edges to see their true form.
- Holes in meshes will confuse the printer, make sure there are no gaps, and that everything has some thickness.
- Intersecting or Multiple objects will not be joined, but will confuse the printer as to which part is to be printed, and what is empty space.
- Surfaces have an outwards direction called normals, which must all point out from the object.
- Overlapping geometry will cause problems, make sure the mesh is clean.
Place a sheet of paper flat on your table. This is our polygon. Now lift up two opposite corners. See how the paper curves? Our polygon is trying to create a flat surface that connects those points. In reality, we would need to fold the paper diagonally to keep the surfaces flat while lifting those corners, which is really creating two triangles. For this reason, it is always best to keep your models made of a maximum of four sided polygons, and ideally in triangles to see it's true shape, as this is how it will be divided up when it goes to print. Also, do not be fooled by any smoothing that the program does. Many programs will try to adjust the surfaces to give an illusion of a curve when it's made of tiny squares. Turn off this to give it hard edges so you can see exactly what will print.Holes in Objects
When printing something like a cube, The program understands that the interior is to be filled. However, if you remove one of the sides, the printer will not know where the printing should stop and will provide messy results. Ensure that there are no gaps in your model. If you need to have an opening, you will need to fill in any interior detail (eg, if you want a hole in a block, you will need to make the interior tube connecting the two sides, and have it attached).Intersecting Objects
Similarly, intersecting objects will confuse the printer as to what is 'inside' and what is 'outside'. Always make your object out of one mesh, or print it in separate parts that you can attach together later. Boolean functions can add/subtract multiple objects, but the resulting meshes can be very messy and require some cleaning up to ensure there are no gaps or incorrect edges/vertices.Surface Normals
Another problem that can cause these messy prints are the normals of your surfaces. Normals dictate what direction a surface is facing. Taking our box example, if the normals point outwards, it will print the box with a filled interior. If they point inwards, it will consider what we see as inside the box to be outside, and will consider the entire rest of the printing area as the 'inside'! (However, without another surface to tell it where to stop, it will be confused and likely just make a mess!).Overlapping Geometry
Sometimes when creating edges/vertices/polygons you can easily accidentally create ones on top of one another. The printer will try to print all of these, so you'll get some very bad results. Selecting all vertices and welding at a very low value is useful for removing any double vertices (and often their adjoined edges). Programs like 3ds max have options like XView (in the Tools menu) for checking for any irregularities on the object.