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Hi,

As it is my first post, I would like to thank Beau for his incredible work ! I’ve been making boards for the past 2 years and your resources helped my out quite a lot.

My question is regarding transition curves from concave drop until kick/nose radius. I’ve 3D printed several molds parts (male and female sides) to test different designs to ensure that there is no gap taking into account concave and radius offset… which is quite difficult !

I’ve tried my mold template on SK8CAD and import the STL on my cad software to see the differences but I’m not able to find the logic/theory to calculate the transition curve and being able to play with the parameters and see wood resistance / compression need for different designs.

Any help ?

Thanks

Hi!

Sorry for my delay in getting back to you here, and that's awesome my work has helped you!
The transition sections are made by creating slices of radial concave, where the radius changes along a Bezier curve. (So, it gradually changes from flat near the base of the kick, then more rapidly changes in height in the middle, then slows down its rate of change as it approaches full concave... and, it's weighted slightly more to change more quickly at the base of the kick - the control point at the kick side of the curve is a shorter distance away from its anchor point than the control point at the concave side of the curve from its anchor point.)
When using SK8CAD (at https://sk8cad.com), the specs you enter are for the male mold, then the female mold is designed with features that are offset from the male mold. The transition section algorithm is the same, however, except that the second anchor point is set by your full concave + your specified offset. While the female technically isn't truly algorithmically offset, this approximation seemed close enough when I compared an algorithmically offset surface with this simplified offset surface, and I've verified it empirically with my own test of pressing a fairly steep deck in SK8CAD molds designed with 3 deck offset.

Right now, I currently don't have any indication of how much force is required for a given transition section geometry. It's tricky to know for sure, but as a general guide, I use another very simplified equation (derived from the equation for calculating strain (https://en.wikipedia.org/wiki/Deformati ... ing_strain)) to check by comparing the length of the transition section to the length of the Bezier curve at the side of the mold (which would require the most stretching of the wood). From what I've seen, it's best to keep the difference in these two lengths divided by the original length less than 0.02. (In other words, if the length of the transition section is 4" and the length of the Bezier curve is 4.2", the calc would be ((4.06 - 4)/4) = 0.015, which is less than 0.02, and most likely an achievable bend.) If this is a feature you'd like to see in SK8CAD, I can consider adding it in - I don't know if it's possible to know for sure given someone's specific pressing setup/process, but I imagine it would be at least a somewhat helpful to get a rough idea.

Let me know if this answers your question!

Hi Beau, apologies for the -very- late answer, I somehow missed your answer. Your answer is on the spot and will be of great use for mold design (as well as fulfilling my curiosity).
Not sure if SK8CAD users are willing to play with the limits of transitions as you already built some controls in the system but it’s a great indicator.
Thanks again for the great work and sharing your time and knowledge.