I am drawing the hull of a plywood hard chine boat with Inventor.
Basically there are a number of boat stations that are drawn in as sketches on parallel and spaced planes. Stations are drawn as series of straight line segments representing the hard chine technique used for this particular boat.
The plank is created as a lofted surface passing through each corresponding straight line segment of all stations.
Surface is then thickened and it becomes a sheet metal.
I am unable to unfold or better to create a flat pattern from the sheet metal. The program correctly complains about the lack of bends in the sheet metal: there are infacts no bends as the plank is a continuous curved surface of which I would like to obtain a flat template for CNC cutting.
If it helps, I doubt the problem comes from compound twisting/stretching of the surface since the stations' geometry comes from an existing design of which several hundred plywood boats have actually been built.
Any suggestion on how to get unstuck would be greatly appreciated...
Solved! Go to Solution.
A snapshot or two would help us to better understand the issues involved, but I think the individual planks are not just one continuous radius, rather they curve smoothly at different radii along the length of the plank. Correct me if this is not so. Inventor (unfortunately) cannot unbend or unroll such a shape. It needs a single continuous radius, whether small or large, to flatten.
I'm quite familiar with the design process you describe.
The first question is "Is the design a truly developed plywood panel or just an approximation?" Even if every station shows a straight line and these are all parallel to each other it's not properly developed - that would only work if every station were perpendicular to the panel and that's not common practice. If the angle of the straight lines varies from station to station it's even less likely that it's been properly developed. Chances are it's not properly developed but with a bit of shimming during construction and a bit of torturing of the panels the boat will come together in real life, as evidently they have. Inventor can't deal with that.
If the panels are properly developed you run into the next limitation with inventor. Sheet metal can unfold portions of a cylinder or portions of a cone, i.e. a constant radius or a linearly tapered radius. Boats will generally be based upon splines with a continuously varying radius, thus can't be unfolded. You would somehow have to mimic the shape of the panel with a series of flat panels small enough that the angular bend is very small, or a series of cylinder or cone segments with the average local radius.
I seriously suspect that if you'r goal is to pre-cut the panel from a drawing you'd be quicker to make a scale model out of balsa, measure and scale up.
thank you for taking your tilme to provide a reply to my question.
You are spot on. I understand now that rather than "unfold" the feature I should be looking for is "unroll" which will naturally imply approximation of the surface in order to produce the flat template.
I know some software programs dedicated to boat design and boatbuilding are out there (I heard of Hulls, FreeShip, DelftShip, Rhino3D). I will look into them.
Otherwise working the templates direcly from scaled down model will be the way forward.
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