Where have we used 3D printing?
In the 2019 season we used a lot of 3D printed parts, and we learned a lot. Here's a list of some of the parts we used, what we used to print them, and what we learned/iterated upon.
Lower Elevator Pulley - this pulley was mounted on a 1/2" Thunderhex shaft and rope was coiled around it. Initially, the part was printed with PETG, which didn't last. The pulley would survive under normal conditions, but as soon as there was a sudden impact to the elevator, such as a programming issue causing it to slam down, the pulley would crack. Eventually, Bruce from Team Mean Machine printed one on a Markforged 3D printer out of polycarbonate. We had no issues with this pulley breaking. We also printed a new pulley from higher quality PETG, and printed the pulley vertically so the layers would not be inline with the stress from the rope, and even though this pulley was untested, we think it would have performed as well or better than the Markforged one.
Upper Elevator Pulley - this pulley had an insert for a bearing and rope would wrap around it once. Initially, this part had a filleted slot for the rope, which was prone to breakage. The part was redesigned using chamfers with the rope resting in a flat slot, which was much stronger. We printed this part out of PLA and had lots of issues with breaking it, but weren't able to reprint it from something stronger later in the season.
Elevator Blocks - these blocks were press-fit into 2x1 and held in with through bolts. They held small bearings that would ride on another piece of 2x1 for our elevator. Through the entire season, we had no issues with the very first ones we printed (PLA) breaking. However, it probably would have been better to go for PETG. The part was printed in two parts.
Vision Mount - we used PLA to print a mount for holding the vision camera. This was attached with double-sided tape and since it had no stress on it we had no real issues with it breaking.
Router Case - we used PLA to print a router case. It was held together with bolts. We had no issues with it breaking.
When should I use 3D printing?
In general, parts with very complex dimensions that don't have a huge amount of load (such as a router case, or the elevator blocks) are good applications of 3D printing. Other parts such as pulleys can be done, but if it's possible to manufacture with subtractive manufacturing (e.g. on a lathe or mill), it generally makes more sense to do that than additive manufacturing, as the part will come out much stronger. If you are 3D printing a part that needs to sustain high load/impact, then you need to make sure you're designing your part so that it can be printed easily and therefore stronger (less complex dimensions and overhangs means parts can be printed at a higher temperature and with thicker layers which means higher part strength).
How should I design parts for 3D printing?
Keep overhangs in mind. Small gaps or overhangs are usually fine, but any overhang >45deg or gap greater than 1/2" is probably going to need support, which is a pain and makes the print come out worse. If you need help judging whether something will print with/without support, ask the person printing the part!
Keep tolerances in mind. Most 3D printers have a tolerance of around 0.3mm. This means that if you create a bolt hole of exactly 1/4", the bolt will likely thread in, which is undesirable. This also applies to Thunderhex.
Keep delamination in mind! Since 3D printers print layer by layer, you need to consider how a part will be printed and how the grain will affect strength.