Maslow Home Maslow Community Garden Newsletter

"unfolding" shapes into plywood panels for boats (and other things)

Something that I have been trying to figure out how to do for quite a while is to design something with a lot of flexed and curved panels (like a kayak) in a CAD and then “unbend” the curved panels into the flat version so that they can be cut.

I’ve been told that Rhino can do this, but it’s quite expensive.

While exploring the new FreeCAD release I came across this video for a plugin looks like it can do what we need:

The possibility for designing boats, trailers, airplanes, anything this way is really exciting. I started a thread over in the FreeCAD forums:

https://forum.freecadweb.org/viewtopic.php?f=22&t=27959&p=226865#p226865

Nothing really concrete to report yet, but I just wanted to let everyone know that this is out there

9 Likes

I wonder if something like Pepakura[1] would work for this use case? Intended for paper models, it allows you to take a 3D digital model and create unfolded patterns that you can then use to recreate the model. It exports to DXF. Runs on windows.

[1] http://www.tamasoft.co.jp/pepakura-en/index.html

4 Likes

I think you’ll find that at least with plywood, you’re only good for a single short arc across a sheet. That combined with the need for strength means that you’re really only able to flex a piece of ply (even a single veneer) in compression in a single direction before the whole thing gets really weak. Looking closely at all the boat plans that I can recall seeing, (not kayaks, they’re literally skinned with planks and are able to torsion much more easily, or hardened skin, not something as initially un-pliable as plywood.)

If there is a compound curve build into plywood structures it’s almost exclusively being used like a plank (long and thin, and still only able to give a slight twist as it bends. maybe 45 deg tops…

ex: https://www.duckworksmagazine.com/07/designs/i550/index.htm

hope this helps,

2 Likes

aaargh, stop trying to make building a boat look easy, i haven’t been of a sailboat in my life, and by now i really want one. I don’t even have a place to sail around here.

3 Likes

Never!

Sailing is where its at!

The bigger the better!

Here’s a bunch of Rich Dicks (©Nick Kroll) and their employees getting (seriously) beat up in this yr’s Carib 600:

I think this is a very good question. I wonder if we should ask the question as a topic on a freecad forum.

There may be a solution which doesn’t require a special software feature. It would be some kind of guideline which describes how to create the model, and how it translates into a cut piece.

Maybe this can be done with onshapes sheet metal features?

I did spend a small amount of time looking at FreeCAD in relation to this topic. It has a “ship” section, which seems to be intended for designing boats. They have example boat designs. I am looking at FreeCAD, because it is the CAD package I have downloaded currently. I think @bar commented on having ownership of the documents. It is less clear which of the online CAD packages enable you to own the 3D drawings. For now, I am going with FreeCAD

None of the example boat designs appear to be designed with a plywood construction in mind, so none of the examples are directly useful for Maslow. However, with the unfold function, it is possible. I do think it makes sense to create some guidelines regarding how to design a boat that can be manufactured on a Maslow. This would concern things like:

  1. LImits of bending radius for a given piece of plywood
  2. How to draw plywood surfaces that can be bent out of plywood
  3. General structural guideilnes
    etc.

The fastest way to do this very generally speaking, as there are an infinite number of approaches not all of which will have the same issues, is to build a model out of plywood. The Gougeons describe the process in their book. There is very high quality plywood that can be purchased and cuts readily with scissors. In some case carbboard might work, but the aircraft ply is actually scalable for stiffness to real world materials one will build in. You can scale and print patterns off your printer, then stick glue them to plywood. One can go further with lasers and actually cut real pieces with intricate details, but as wonderful as that looks it is faster to just cut the pieces at the full length after they have been assembled from panels. You can in a few hours model boats that will take a long time to build, and get real results that are NASA difficult to model in computers. It is also the case that computer outputs are not always the best building format, as they eliminate many integrated techniques that would be crazy difficult to model in a real way, but are easy to make in the real world.

Here is an example of both the benefits of making models and the pitfalls of getting too far from the realities of proven techniques, though as an Artist, Brian can gain a ton of followers with his exquisite products. Literally he could have built the hull for a fully compounded 30 foot trimaran in the time this product will take.