Printing SK8CAD Molds Part 1: Designing the Files
SK8CAD is a tool created by Open Source Skateboards that allows you to design skateboards and molds right in your web browser and download the digital files for making them: STL files, for 3D printing or CNC-machining molds, and SVG files for creating templates or CNC-cutting boards.
Skateboard design isn't always been totally clear, though... which can make using SK8CAD a little confusing. In this first post of a series about how to 3D print molds with SK8CAD, I want to clear up the design process a bit by sharing how I approach board and mold design. Here we go!
(Oh, one quick note - be sure to reference the user guide for explanations of each parameter: https://sk8cad.com/user-guide.html.)
-- For the video of this process, scroll to the bottom of this post. --
1) Start with the board specs, and define the easy-to-measure dimensions on boards you like to skate: width, wheelbase, nose and tail length, and concave style and drop. If you're planning on making boards in multiple sizes, choose either the most important size to base your designs on, or the median size.
2) Next, address the less straight-forward specs: nose and tail angles, kick radii, transition length, kick gap, kick concave, taper points, and nose and tail shapes. You may rely more on aesthetics for some of these (however, be aware that wood cannot bend in any position - so try to avoid very tight bends unless you're willing to potentially experience an unsuccessful press). Feel free to check out and use some of the example boards options in SK8CAD for reference. If you're using other boards as references and want to create a similar feel or combination of feels, you can get some rough measurements using some basic tools as I outline here:
(A quick note about this video: boards may have more complex geometry, so you may need to make some approximations.)
3) Once your deck is designed, you'll need to define your mold (depending on your geometry, SK8CAD may have prompted you to change some mold specs already). The mold consists of a male piece and female piece, so that when they are pressed together, the material in between them can take form.
Mold width: I generally like to make this at least around 0.5" wider than the widest board I plan on making. It doesn't matter whether you veneers are wider or narrower than your mold width. Just keep in mind it may be more challenging to arrange/center the veneers in your mold if they don't stick out a little bit.
Mold length: Similarly, I try to make this at least around 0.5" longer than my longest boards.
Mold height: For 3D printing, I try to make the molds as low as possible, which will give me the fastest print times. Then, I'll add a backing board and additional buffer material when actually pressing the molds to reduce any chance of the molds bending.
Mold offset: The male and female molds should not be identical "mirrors" of each other - for example, the male mold may have a specific kick radius, yet the female mold must have a larger (offset) radius to provide a proper press. The offset is the equal to the thickness of each board times the number of boards being pressed, plus the thickness of any other materials in the press. The male mold will have the geometry you enter into SK8CAD, and the female mold will be automatically offset based on the offset value you enter (don't change your specs when you switch between male and female molds!) I typically recommend only pressing one deck at a time if you're doing a glue-up by hand using a glue like Titebond 3, simply because the glue's working time is not very long (the glue starts to set within 7-9 minutes). However, I've heard of people having success pressing up to 4 decks when gluing by hand. Keep in mind the more veneers you press, the more force is required to bend them. Also, the more decks you press at a time, the more variation you'll feel in geometry (the boards closest to the female mold will feel mellower than the boards closest to the male mold).
Skateboard mold offset.
Truck holes: Having the ability to drill the truck holes right through the mold is pretty amazing and saves time, so I'll add these in, using the default 3/16" (0.1875") hole diameter. Even if I'm going to make boards with different wheelbases, having at least one wheelbase built into the mold is super helpful. (You may want to make these holes bigger to install drill bushings to increase durability of the molds.)
Alignment notches: I add these in just to have another form of registration for marking the board before taking it out of the mold (particularly useful if not using built-in truck holes).
4) Once the mold design is finalized, check out your male and female mold files. (Note: SK8CAD isn't always perfect, so if you find a model looks like something is wrong, you may need to tweak either the model resolution parameter or the kick concave resolution parameter. If neither of those resolve the issue, you'll need to slightly tweak one of your board parameters, like wheelbase, kick gap, etc. - even a change of 0.01" can sometimes be enough. Read more here.)
5) If all looks good, you can either download the STL files as-is, or break your model into sections in SK8CAD to fit on your printer. (Some slicer software programs allow you to split models in their software directly, so you may have options!)
Print Section Width: Enter the width of your print area. If your print area width is smaller than your mold width, SK8CAD will divide your model in half so it will fit on your printer.
Print Section Length: Enter the length of your print area. This defines how long to make each print section.
Mold Bores: Use this option if you'd like to print bore holes in the backside of your molds, which can be useful for mounting the sections to a backing board.
Threaded insert installed in bore hole.
Bore Diameter: How big to make the bore holes. I like to use heat-set threaded inserts, and the recommended hole diameter can be found on the supplier's website.
Bore Depth: How deep to make the bore holes. (If your mold is thinner than the board hole depth anywhere, the bore hole will become a through-hole.)
Bore Spacing: The distance from the center of the bore hold to the edges of the mold.
Section to Download: You'll need to download each section. Depending on your mold size and print section length, you may need to download the "extended" nose/tail sections, if your mold is too long to be split among the other sections.
Lastly, prior to each download, you may want to update your filename to more easily see what's what.
6) That's it! I recommend recording your design (we're working on enabling saving soon), so you know what you did, before closing out of SK8CAD. You can also download the SVG template if you'll be using that to shape your board.
Now, you can move on to preparing your files for printing.
Want to watch the video of this process? Check it out here:
Part 2: https://shop.opensourceboards.com/blogs/blog/printed-molds-prep
Part 3: https://shop.opensourceboards.com/blogs/blog/printed-molds-assembly