Today we printed our first parts. We decided quickly to use the FDM process to make our parts. Besides the sufficient number of printers in the lab the mechanical properties of FDM are good and the material is affordable. In addition to it we thought about the open source idea of this project and since FDM printers are fairly common as home user devices it should give the best opportunity to replicate the Trebuchet. Before I explain more about the print itself we want to introduce you to the equipment we used.
Printer: LulzBot™ TAZ 5
We decided quickly which printer we wanted to use based on these reasons:
- Biggest available build platform
- Arm length = 25 cm
- Parts printable in fewest prints as possible
- Best available accuracy
- Reduce post processing
- Reduce friction between slide and vertical track
- Fastest print speed
Software: Cura LulzBot™ Edition 17.10
Within the decision to use this printer we used the recommended software Cura LulzBot™ Edition 17.10. The Cura software is an open source software which can be adapted as we need it. So were able to set different print parameters as well as the orientation on the print bed.
Another advantage of this software is the possibility to have a look at every single layer and to determine where we need support structure.
Parameters:
- Layer height: 0.3 mm
- Because this is our first design and to reduce the build time we decided to choose a higher layer height which leads to a rougher surface
- Shell thickness: 1 mm
- Since the nozzle size is 0.5 mm we picked two outlines to stiffen the parts more than it is possible with one outline
- Fill density: 20%
- Due to the fact that the shell thickness is 1 mm we wanted to try as little infill as possible and picked 20%
- Print speed: 50 mm/s
- Highest available print speed
- Material: Matterhackers Natural ABS 3.00 mm
- Good mechanical properties
- Printing temperature: 250°C (recommended)
- Bed temperature: 110°C (recommended)
- Support type: Touching buildplate
- While designing the parts we considered the specific design rules for 3D printing and tried to avoid overhangs and undercut features. The pin at the end of the hook is the only part which needs support structure underneath.
- Platform adhesion type: Brim
- To increase the adhesion to the build platform and considering the fact that most of the parts are fairly large we decided to use a brim around the parts.
All of the parts don’t fit on the platform at the same time. Because of that we printed two times with the same parameters. The total estimated build time is 8h 8min + 3h 24min = 11h 32min.
After the print we saw that we made the parts a little thicker than they need to be and that the Trebuchet looks too massive. Most parts assembled well, our upright (vertical track) needs to be sanded down to fit into the rails. The outriggers pressed in a little hard but made it. To reduce the shrinkage and warpage of the parts we decided to switch from ABS to PLA. Doing this we have to keep the mechanical properties of the parts under review.
The Surface looks very good and not to rough. The friction between the slide and the vertical track doesn’t seem to be a problem. That’s why we decided to stick with 0.3 mm layer height
Since the parts are probably too thick and one of the requirements of this project is to optimize the build time we decided to try and reduce the build time. Our goal is to print the whole Trebuchet in half the time we need right now. We’ll see where we can cut material.
