I made a board template using a 3D model in SketchUp and exported the top-down view into Layout for printing. The plan was to use it as a cutout for shaping. But I realized something, since it’s a flat, top-down view, once you cut the rocker into the blank, the template doesn’t sit perfectly on the foam anymore. There’s a small mismatch, especially at the nose.
It’s not a big deal on flatter boards like a fish, but on something with more rocker, I think the error would be more noticeable.
So my question is:
Do you usually trace the outline first, then cut the rocker?
Or do you just deal with the small distortion from the template not matching the rocker?
Also, any tips on how to improve a SketchUp-style template? Like scaling, alignment, adding rocker points, etc?
And lastly, is there any other info I should include in the template to make it more useful for hand shaping?
Thanks, although I must admit that the real distortion is in the nose, so theirs no big deal. The tail should remain rather non distorted. The whole template only falls of by something like 0.5cm. But I’ll look through the whole thread to look how to deal with more extreme cases, where it may actually matter.
Step-by-step (how to get rid of rocker distortion in sketchup and layout):
Create the top-down outline in Layout, using Vector mode for clean export.
In SketchUp, extrude your rocker profile to build a rough 3D foam blank.
Import the vector outline (exported as DXF from Layout), position it above the foam, then extrude it down and use Intersect Faces to cut it perfectly into the curved rocker.
Use the Unwrap and Flatten Faces plugin (free extension/plugin) to unwrap the curved shape and flatten it into a proper 2D cutout.
Send that final flattened shape back to Layout for printing a proper template that actually accounts for the rocker.
It would be interesting to see the delta between the top view plan shape and the unrolled bottom surface, using either the mid point or wide point as a common reference.
BoardCAD has a ‘plot over curve’ function, I cannot remember if the commercial programs do as well.
I am sure I have templated a board or two blissfully ignorant of the increased length over the curve.
Thankfully, SketchUp has a few plugins that handle this pretty well once you start digging. On this board, the distortion (for an “on-top” template) came out to around 0.402 cm , not much, since it doesn’t have a ton of rocker (on top-side). Even in the most complex part of the shape (the tail), the difference was barely 0.002 cm, so basically nothing to worry about.
Honestly, even if someone didn’t correct for the distortion, as long as they were aware of it, they could probably handle it just fine by eye when shaping. With no real effort.
That said, it would be interesting to test this on something with way more rocker, like a longboard or a modern step-up, and compare the delta. I could imagine the difference adding up a lot more over the length.
My friend’s already bugging me to shape a longboard too… so maybe I’ll tackle that in September and find out. Could be a cool comparison.
Edit: Sorry, really tired. You meant the unrolled bottom shape vs the top view. Yeah I reckon the’d be bigger difference. I think that would be an interesting comparison. I unrolled the top surface for now. Might as well flesh out my template even more tomorrow and unroll the bottom side tomorrow.
Here is the stock longboard from BoardCAD LE, presented in metric units, showing some of the differences between straight line and over the curve measurements.
Don’t forget that most important curve is rocker then foil then outline. First design rocker then design top curve to have foil you want then design outline you want that go clean with rocker/foil ever design.
I did the bottom side of the board… the difference between the straight line and the curve of the rocker is just 1.416cm. Nothing too major. I actually thought it may be more. Might as well include the adusted plans in my template on a third page.
@jrandy Even in your example on longboard. The differnce is just 2cm, perhaps my OCD blew up this problem in my head.
Yeah you lost me on cm’s. By the time you over analyze this board you could have shaped it. Is this the first surfboard you have ever even thought about. I would guess so.
