A disc is easy to model by revolving a profile. Below is a disc profile. The many dimensions on it were necessary to completely define the upper spline curve and the space between it and the offset curve below it (which determines the thickness of the disc). Where you see “fx:” in front of a number it just means that number was stored as a parameter; the number shown is simply the value of that parameter. The dimensions without “fx:” were calculated by the drawing program based on where the control points were dragged and were recorded as-is. This sketch was drawn in Fusion 360TM:
Drawing a profile is easiest if there is a layout line vertically through the origin and another through the center of the disc profile. These layout lines are for adding dimensions to the disc and are shown as dotted lines (which on the left and right appear under dimension lines).
Once the profile is created it is revolved into a solid body. You can see the profile and the solid body in this image:
One can easily edit the sketch to change the shape and thickness of the disc. If the skin is 1 mm thick, the disc is very light but somewhat fragile, at least when printed using PLA filament. A 2mm thick disc is much less fragile but it is also heavier, which changes the flight dynamics. The heavier the disc the more stable it is, especially if it has good spin. You can experiment with skin thickness and how much plastic is around the rim. The disc above could have a filled in edge which would give it a little more gyroscopic effect and make it heavier, which would make it fly straighter.
A 1mm thick skin that was 70 mm in diameter took a little over one hour to print on a Prusa Mk 2.5 3d printer. A 2mm thick disc of the same design and diameter took a little over two hours to print on the same printer with the same settings.
Here is the finished disc model seen from an oblique angle (with a shadow that helps show the disc shape):
Next up: Printing SDG Discs