Along with the various complications involved with 3D printing, the first step in making sure you fabricate a clean print is making sure it was designed with additive manufacturing in mind.
The most important factor in having a smooth print when designing your part is to factor in the angles and overhangs involved.
Since FDM 3D printing melts plastic onto a print bed layer by layer, any extreme angles will require support material. This support material can be thought of as scaffolding that will break off and be cleaned up post print.
While settings can be dialed in to prevent as much scarring as possible, you can see that there is no way to avoid some minimal scarring.
Each material has it’s own angle that will require support material, but it is safe to assume anything with an angle more extreme than 45° will need it. Limiting the amount of these overhangs will limit the amount of scarring as well as limit the amount of post print cleanup.
The issues of overhang lead into our next tip of designing for 3D printing – having a flat surface to start the print on.
Starting with a flat surface allows for not only good bed adhesion, but will drastically improve the print quality.
Imagine you design a very detailed sphere. This surface area of a sphere touching a printer build plate is infinitely small, meaning the first layer will only be a dot as thick as determined in the printer settings. This means that there will be support material required very close to the build plate and will ultimately lead to poor surface quality.
3D models can often look great to the naked eye, but they will not print properly at all. This is because they were either combined incorrectly, exported improperly, or had some other issue that cannot be explained.
You can determine if your model has errors by either downloading software such as Netfabb, or running it through Netfabbs model correction tool. If these corrections are not fixed, we will not be able to print your part.
Clearances and printer limitations
It is important to remember that 3D printing has it’s limitations. Since FDM printing involves the melting of plastic through a nozzle, tolerances are limited to a few factors.
While we will go over this further in our quality selection video, the smallest nozzle we can print with is 0.25mm, while we go up to 0.6mm for lower quality. This means that any detail or wall that is thinner than the nozzle diameter will not print. If your model has walls that are 0.3mm thick, but you order draft quality, those 0.3mm thick walls will not be noticed by our 0.6mm nozzle, and therefore will not print. The same is true for logos and text that are on a print. Anything in the XY direction requires a thickness of at least the nozzle diameter.
This leads into adding a clearance for parts that mate together. Since 3D printing is additive, it tends to err on the side of more material than less material. This means that if you design two parts that were meant to perfectly mate together, they will not. We describe this tolerance as ½ the diameter of the nozzle.
So if you were printing your part in draft resolution, which means we will be using a 0.6mm nozzle, the clearance required for parts mating together would need to be at least 0.3mm. The same is true on finer resolution prints, just with a tighter tolerance.
This is crucial to factor into your part before submitting for printing, because there will be no way for our team to recognize this until after it is printed. Then you will be left with a lot of sanding.
While this is always getting larger, 3D printing, especially the machines we use in house, are limited in their build volume. The majority of our production machines are around 10” x 10” x 10”, but we have a couple of specialty printers that can get up to 15” in all directions.
We are able to print parts larger than this, as long as they can be sectioned up and plastic welded together after printing. We can then bondo and spray paint the part to look as though it is one unit, but it will have an added cost and not be as mechanically strong or accurate as a part printed in one piece.
While these steps may seem like a lot to comprehend when first getting used to 3D printing, you will start to notice how these rules become intuitive after a few designs. These design limitations will also decrease over time as the technology around 3D printing gets even more advanced.