Printing SK8CAD Molds Part 2: Preparing the Files & Printer

An important step in 3D printing is preparing your files to be printed - creating the instructions for the printer to make your 3D files via "slicer" software. I'm going to outline the process using PrusaSlicer, the slicing software I use, but don't worry if that's not what you use - settings are very similar between FDM* printer slicers, so this information to still be useful.

*FDM, or "Fused Deposition Modeling", printing is currently one of (if not "the") most widely used and most economical 3D printing processes available.

-- For the video of this process, scroll to the bottom of this post. --

1) Import your STL file and scale it correctly. STL files are unitless, so you need to tell your slicer software what units the file was based on - in our case, SK8CAD is based on inches. Often, slicers assume mm, so you may need to scale uniformly by 2540% (1 in = 25.4 mm).

2) Select your printer and/or nozzle. The printer nozzle is the part of the extruder where the plastic comes out; this is what defines how thick the plastic extrusion is. By default, my printer came with a 0.4mm nozzle. Nozzle diameter impacts print resolution and speed: the larger the nozzle, the more material you can lay down, and the faster your print will finish; however, a larger nozzle won't be able to achieve fine details - it's like using a marker (large nozzle) vs. a pen (small nozzle). I purchased a 0.8mm nozzle specifically for 3D printing molds. Thankfully, PrusaSlicer has a preset option for their printer with a 0.8mm nozzle, so I used that as my foundation for my slicing settings.

3) Select your filament. I've mostly printed with PLA, which is a firm and more naturally-derived filament than some others (it smells way less bad than some other plastics when heated). PETG would be another good option, which is more durable than PLA (but a bit more flexible).

4) Adjust the print settings:

Infill: I've printed a mold at just 10% infill and have had success loading it under two fully-jacked 20-ton bottle jacks. 10% seemed like enough for my purposes. I may increase it to 11%-15% for some thinner sections just so they're not as fragile to handle. This helped reduce my materials cost and print time. Check out Chris from Good Roads' video for testing infill densities:

Infill pattern: I either use rectilinear or gyroid. I believe rectilinear is slightly stronger in the direction molds are loaded than gyroid, but I noticed gyroid used a little less material and was faster for some of my prints. Here's another helpful video, this time from CNC Kitchen, showing the strengths of different infill patterns:

Horizontal shells / solid layers: I removed the top and bottom shell from my print so that there was no material covering the infill. This reduces print time and materials cost.

Skirt: Having a skirt with at least one loop is nice to clear out the nozzle before the print starts, so I recommend using a skirt.

Trimming the middle male sections: Lastly, I trimmed off the bottoms of the 3 middle male sections to reduce print time and material cost. To make up for the difference in height from the nose and tail sections, I used surfaced pieces of plywood as a spacer between these mold sections and my backing board to ensure the surfaces still matched up. ("Surfaced" means the sheets were precisely cut down to the specific thickness I needed; this could be done with a CNC router (or manual router and jig) or drum sander.)

Notice the extra plywood "spacers" below the three middle male mold sections.

Once I export the G-code (printer instructions) from PrusaSlicer, I prepare the 3D printer:

1) As I mentioned earlier, I prepare the files based on a 0.8mm nozzle, so I install that size nozzle on my printer (if not already installed). Refer to your printer's instruction manual for the details on how to safely change the nozzle.

2) Apply a thin layer of glue from a glue stick on the print bed to ensure PLA prints will stick; since the footprint of these mold sections is fairly large, they are more likely to warp. By applying a thin layer of solid glue, the print is held to the bed more securely to prevent the edges from peeling up due to warping.

3) Grease the linear bearings, which helps mitigate a potential "layer shift" - when the printer has a mechanical glitch that causes the model to shift sometime during the print, rendering the part useless (in most cases).

4) Check to ensure there is enough filament and/or that the filament sensor is working. If your printer has a filament sensor, it will likely have a setting that alerts you when it's about to run out of filament so that you can replace it. If not, you'll need to make sure that you have enough, so your printer doesn't keep printing when it runs out.

While that may seem like a lot of prep, you'll get the hang of it with some practice. Plus, that's pretty much all the work - the next step is to push "start" and let it print!

A final note, in case you're wondering "How long do these parts take to print?"...

Here are the print times with the settings I used:

Center female section, thinnest section: 1 hr, 24 min / 77g filament

Center, male section, before trimming: 6 hr, 33 min / 398g filament

Center, male section, after trimming: 2 hr, 10 min / 130g filament

Nose, male section: 2 hr, 17 min / 135g filament

Nose, female section: 2 hr, 59 min / 177g filament

Need print supplies? Check out MatterHackers.*

Part 1: https://shop.opensourceboards.com/blogs/blog/printed-molds-design

Part 3: https://shop.opensourceboards.com/blogs/blog/printed-molds-assembly

*Disclaimer: Open Source Skateboards receives affiliate commissions for purchases made through MatterHackers links on this website.