For this assignment I decided to print an articulated slug. The first thing I needed to do was resize the .stl file. When I opened the .stl in CAD, it was measuring 110in in length. So I scaled it down to about 1.875” in length. I was short on time this week, so I knew I’d probably only have one shot at each print (FDM and SLA). If I anticipated having time to iterate, I would have liked to have made my little guys a bit bigger. I think they would have been more fun bigger, and once they were rolled up I know I could fit a bigger slug in the container, but I wasn’t sure how much bigger. Wanting to avoid printing, fit checking, and reprinting, I decided to scale the parts such that they would fit in the containers without bending at all.
After scaling, I started with my FDM Prints. In the slicing program, I adjusted the settings and also added a brim to help with printing. Here are some images of the process and the prints as they came off of the printer.
After removing the brim, including the bits the spanned the different segments of the slug, I was able to articulate the parts.
Then for the SLA parts. I decided to print 3, to have some extras in case some had problems. And I did end up having problems with these parts. I’m not sure why, but my SLA parts came out very frail and brittle. When I tried to articulate the first one after curing, I immediately snapped it in half. I was able to be more careful with the other two and get them to articulate some, but not much. And I can see that some of the movement is just due to cracking in the parts, not actual working joints. I included an extra FDM slug in the container with the SLA one, just because I’m pretty confident the SLA one will break quickly, and if someone gets that from the machine now they’ll at least have one that works. I’m not sure if it is just the size of the features that is causing the fragility, or if maybe the cure contributed. I put the parts in for 15min at 80C, according to the recommendation. However, when I started the curing oven, it took a long time to preheat. So the parts were in there for about an hour as it preheated to 80C, and then 15min longer after that. I don’t know if this extended cure affected the strength of the parts or not.
All in all, I wish I would have made my parts bigger, and I also wish I had the chance to re-do the SLA parts, but I’m pretty happy with how my FDM little guys turned out.
| Cost Type | Cost | Price | Source | Quantity | Total |
| Materials and Machine time | FDM | $8.00/cubic inch | OEDK | 1.5 cubic inches
(6 slugs) |
$12 |
| SLA | $3.00/cubic inch | OEDK | .75 cubic inches
(3 slugs) |
$2.25 | |
| Labor | Prototyping Engineer | $38/hr | Ziprecruiter.com | 1.5hr | $57 |
| Total | $71.25 | ||||
