# Design Rules for Successful Prints ## expand\_more After your first print, you will probably want to print more and see what are the other possibilities with this printer. Yes, there are many possibilities and lots of objects to 3D print. However, there are some rules in 3D silicone printing that will help you to get successful prints. Because not all the designs are 3D printable with our silicone printer. Compared to conventional FDM printers our ink is affected by gravity a lot. A successful print depends on an understanding of the 3D printer limitations and designing the CAD file of the print accordingly. With this system, the print process had to be fine-tuned. The silicone material had a major role to play in this. Every G-code path generated by the slicer software used must be considered for print success. Disconnection between print paths and jumps between print spaces will cause distortions in the printed shape. The following design rules have been determined from our print processes. Design rules are marked from D1 to D9 and slic3r settings marked from S1 to S19 in the tables down below. Sort **Design Rules** **Rule #** **Rule definition** **Parameter** D1 Minimum feature thickness on XY plane 1.5 mm D2 Minimum layer thickness in Z direction 1.3 mm D3 Achievable concave pitch range 70 - 90 degrees D4 Achievable gap spanning 2 mm D5 Minimum cross sectional area of a layer 625 mm2 D6 Minimum time between layer 30 - 60 seconds D7 Minimum achievable circle diameter 3 mm D8 Minimum achievable wall thickness 2 mm D9 Minimum achievable horizontal air chamber cross section area 3.9 mm2 In terms of design rules, the printer have 9 main limiting constraints. Rule D1 basically indicates that if the designer came up with 1 mm thick feature in the CAD file printer will print it as 1.5mm due to nozzle size. It is currently a hard problem to reduce nozzle size because the silicone material cures faster with a smaller nozzle diameter. Rule D2 brings a limitation to the layer height. For example, if the feature has 3mm thickness, the printer will print it in two layers, which may lead a weak spot. As a note, a 3 mm wall thickness is optimal for pneu-net walls. According to rule D3, slope of the wall should be in between 70 and 90 degrees. If the designer came up with a 45 degree slope in the CAD file, since the printer is not using any support material, the feature will fail to exist. The gap spanning (Rule D4) is the one of the important feature that shows the quality of a 3D printer. In silicone printing case, spanning 2 mm gap without overhang is a great success. The designer can come up with a CAD file that has 2 mm ceilings over air chambers. D5 and D6 are one of the very important rules and they are connected. If the print feature is too small, this will mean that the extruder will move on the next layer in a very short time which will happen before extruded layer cured well. Due to this fact the limitation D5 or D6 must be followed for thin and tall structures. Rule D7 is caused because of attraction between extruded silicone lines. When extruder head follows the circle path, the edge of the dispensing tip pulls the silicone material close to each other. Due to this fact we observed a limitation in the achievable circle diameter. In terms of creating soft robots, wall thickness is really important due to inner air chambers for actuation. Outcome of our experiments lead us to rule D8 for minimum wall thickness in CAD design. The last rule emerged by combining rules D1-D3 and D8 to come up with horizontal air chamber designs. These chambers are vital for a soft robot to operate and by following the rule D9 it is easy to 3D print them. #### Software settings After following the design rules, it is necessary to check the settings of your gcode software called "sli3er". Effective print settings in Slic3r is a challenge because all currently available slicer programs were designed for printing thermoplastics. To avoid main problems such as over-extrusion, cloaking, under extrusion and gaps on the corners these software settings will be your guide. Please check the table below. (We also provide the troubleshooting guide at the very last section of this project) Sort **Sli3er Settings** **Settings number** **Settings** **Parameter** S1 Layer Height 1.3 mm S2 Minimum # of Perimeters 2 S3 Seam Position Nearest S4 Fill Density 100% S5 Fill Pattern Rectilinear S6 Fill Angle 45 or 90 degrees S7 Perimeter Speed 7 mm/s S8 Infill Speed 7 mm/s S9 Travel Speed 50 mm/s S10 Default Extrusion Width 140 % S11 Perimeters & Infill Overlap 40 % S12 Filament Diameter 1.65 mm S13 Nozzle Diameter 1 mm S14 Pump Flow Rate 26 ml/hr S15 Heat Bed Temperature (HBT) at First Layer 20 C S16 HBT for Rest of the Layers 50 C S17 Heater Fan (HF) Speed 80 % S18 Initial Heater Temperature (object height below 3cm) 50 C S19 Heater Temperature (object height above 3cm) 80 C When over extrusion problems occur the printed shape expands and mismatch between CAD file and real object is inevitable. To prevent overflow the setting S1, S5, S7-S14 should be followed. The most important rule is S14. If the pump flow rate is too high, the shape will become bulky. Certain desired settings, such as a larger extrusion width relative to the nozzle diameter to compensate for silicone flow, were not allowed in the software. This requires clever manipulation of settings to get to the desired settings. When cloaking problems occur, the silicone flow will from the nozzle will start to slow down and get thinner, in couple minutes flow will stop completely and pumps will stall. To prevent cloaking the settings S12 - S19 should be followed. Sharp turns over 90 degree can often lead to holes in the print layer because adjacent silicone roads will not come in contact and extruded silicone lines will pull each other. There are several workarounds for this to prevent the gap problem for the sharp corners of the designed shape, the setting S2, S3, S7-S9, S14, S15 should be followed. The settings from S17-S19 are not located within the software. You will need to arrange them manually in the control panel of the heater wings. These settings are not necessarily the final settings. What you need to do is to experiment with them and see which parameters are working the best for you. Feel free to ask any questions over the contact info section.