About Scaffolds/Supports

3/11/2018

Left over supports from a failed printHappy Daylight Savings Time everyone!

For this week's post, I decided to talk more about 3D printing scaffolds. I talked about it briefly in the article "Lyforms Small-Scale Modern Era Kit Design Process". I wanted to use this as an opportunity to expand upon that a little more.

Here is what I say about scaffolds or supports in the article:

  • The structure pieces are laid out in such a way so that they can be printed with minimal amounts of scaffolds. For example, the walls for buildings are usually printed flat rather than standing on their ends.
  • If an overhang is required, then support scaffolding is created in the CAD software to make them easier to remove.
    • Scaffolds in 3D printing are support structures that are printed to support parts that extend outward as part of the object being printed.
    • When the material is extruded by the 3D printer nozzle, it is heated at high temperatures and comes out as a melted, soft state.
    • This requires a support structure to hold the melted material in place until it has cooled.
    • Scaffolds are meant to be removed easily after the object printing has been completed, so they are usually very thin so that they can be cut or broken away with a hobby knife.

Scaffolds or supports are a necessary complication that comes along with the 3D printing technology called Fused Deposition Modeling (FDM). The concept behind FDM involves melting a filament and extruding it through a tiny nozzle onto a build plate along a path dictated by the digital design of the object being printed. It works in a way very similar to a hot glue gun, but instead of your hand guiding the glue gun, it is done by a machine following coded instructions.

After the material comes out of the 3D printer nozzle, it cools and returns back to its more rigid state. The 3D printer lays layer upon layer of the printer on top of each other, slowly building up the object until it is completed.

Since the filament material comes out soft, it requires something to support it until it can cool. When the object only requires each layer to be directly on top of each other, this is not a problem as the cooled lower layers support the hot top layer.

But what if the object has something like an over hang that doesn't have "built-in" layers to support it? This is where scaffolds or supports come in to play. Lower level scaffolds are created in the digital design of the object to support the upper levels of the object. Their function is purely functional: aesthetically, they don't look anything like the object. They are only meant to serve 3 purposes:

  1. Support the object's over hang
  2. Break away easily, and
  3. Use as little material as possible.

Use as little material as possible? You mean the printer has to actually print the supports with the same material that is used to print the object? That's a HUGE waste of material!!

Yep. Bummer, isn't it? But that's OK, because, as you can imagine, a lot of people smarter than me have figured out ways to work around it. I'm going to explain some of them below.

Massive Overhang Test

Most FDM printers available on the consumer market have gotten to the point where they can print overhangs without support at pretty high angles. There is an object available for download on Thingiverse.com called the massive overhang test that will test the thresholds of your printer. It looks like the tines on a music box or the pipes on a pan pipe. Each tine or pipe has an overhang at the end at increasingly larger angle degrees. This will tell you how far you can go before you need to consider inserting some supports.

When I ran it on my printers, I discovered that it could print up to a 55 degree angle before it started distorting and losing shape. Knowing this, you can check your objects on the computer before you print to see if they are 55 degrees or higher, thus minimizing the amount of material that is wasted on supports. This is important when designing your own objects, which brings us to....

Design Angles

When I design model kits and parts for Lyforms Small-Scale, I take the overhang threshold into consideration before I print them. As I mentioned, this allows for less material to be used, thus cutting back on costs. There are several ways to do this.

When designing an overhang, I usually make an effort to use an angle that 55 degrees or less. An example of this is in the blog post "Water Towers, Part I". Most of the time, this doesn't require many aesthetic compromises.

In situations where a shallow angled overhang just won't look right, I will look at ways to cut the object into pieces on the CAD program so that I can print them in a position that won't require supports. An example of this is taking the flat walls of a building, breaking them apart, and printing them flat on the build plate, as explained in "Lyforms Small-Scale Modern Era Kit Design Process".

Sometimes, neither of the above will work, especially if it is an object that is designed by someone else. Then it's time for....

DIY Supports

When there's no choice but to print an object with a large overhang that is beyond the threshold of your 3D printer, you can handle it in a few ways.

If you designed the object yourself, you can design your own supports in the CAD program. This allows you to create scaffolding that uses minimum material while providing maximum support. You also want it to be easy to break away from the object after it has been printed. I usually design supports that look like cones with the points touching the underside of the overhang. These break away easily while still providing a wider base for support on the build plate.

The other option is to let slicer software insert supports for you. As explained in "Lyforms Small-Scale Modern Era Kit Design Process", slicer software converts your CAD design into the machine language that the 3D printer will read to print the object. Most slicer software will identify overhangs automatically and insert supports. Some slicer software will allow you to add or reduce supports as well. This is very useful for objects that are downloaded from the internet and designed by someone else. These supports are typically very thin and easy to break away from the object after it has been printed.

Other Options

One of the other interesting options for printing supports is to print them using a material different form that used to print the object. High Impact Polystyrene (HIPS) is commonly used for supports because it dissolves easily in limonene, eliminating the need for scraping or cutting away support materials. Of course, this is only possible on printers that have two print nozzles: one for printing the supports, one for printing the object.

Whew! This post was a long one! Thanks for sticking with it. I hope that it gave you a different "angle" on 3D printing!

-Rafe