Sedia 14 Thonet (Chair no14) part 2

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Part 2

Now we got rid of the troubled meshes and retained the crucial information they gave.

It is easier to simply use the Loft command, select all the circles and Rhino Will generate the back frame polysurface. That’s what I did.

For those Who want to know how to obtain the spline that defines the back frame, I’ll explain briefly.

Use the curve by interpolate points command and tick only Center on Osnap, with Project and STrack off.

Obtain the back frame polysurface any way you prefer (Loft, Pipe, Sweep 1 rail)

OK, we got it. Disappointedly though, the polysurface comes a bit deformed to. The deformation is visually clear, it spoils our hope for a perfect model. Thinking how to get through to it led me to writing in the FlyingArchitecture forum seeking for help. This is a little ingenious solution I formulated for it.

In a curve made by interpolate points, the more points you create, the more it gets deformed if the points are not properly aligned to the correct shape.

These two curves are identical, but the upper one is composed of more points.

If we purposely disarrange some points of both curves, the curve with more points gets much messier and more deformed than the curve made by fewer points.

In the image above, the bottom curve, in yellow, is the original shape. Both upper curves had some points altered. It is much more evident in the curve with more points, and subtler in the curve with less points.

The same principle applies to our bentwood back frame. When generating the mesh triangulation to export the model to dwg format, the original software where the model was done denatured the original correct shape. To overcome this inconvenience, the solution is simple: we should delete some circles we Drew.

After some experiments, I arrived at this composition: