Hi Arthur, so I've been looking more deeply into why your original sweep example (The A400M Propeller Example.3dm file that you attached previously) doesn't work right, and I've found a couple of problem areas. The good news is that there is a way to work around them.

The first problem is that the sweep goes through a routine in the geometry library that decides that any edge smaller than 0.001 units is degenerate and that edge just gets left out of the trimming boundary.

So to avoid that, increase the size of your object until the smallest segment in it is at least 0.001 units or larger in length, probably best to have a bit of cushion on that so maybe target something like 0.01 units. This part can be done easily to your example file by just switching your unit system from meters to millimeters (as long as you have not turned off the option to scale objects when the unit system changes which is enabled by default).

So that's the first step - switch to units = millimeters.

Then the next thing that goes wrong is related to having not just one tiny segment but actually having 2 tiny segments right next to each other like this:



Instead of having little arc segments one after the other like that, you've got to delete those 2 little pieces and instead put in 1 single arc piece in there instead (something that Burr tried earlier also), like this:



Having 2 little tiny segments adjacent to one another causes a problem with the joining stage - sweep basically builds one surface for each segment of the profile being swept and then does a joining process to glue those surfaces together into a connected piece. But with those 2 little segments side by side, they end up actually being within the join tolerance of each other and the joiner goes ahead and glues them to each other making a mess in this case. When you have only one little edge in there that won't happen. So getting just one arc piece instead of 2 arc pieces like in one of Burr's previous tries is another key thing.

To replace the arcs, use Edit > Separate to break the curves apart into their segments, delete the 2 little arcs, and use Draw curve > Arc > 3 pts to put in a new larger arc there, then join all those segments together into a closed curve.


I've attached an updated version of your file which should now sweep file - so again the steps to alter your file are - switch units to millimeters, and replace the 2 little side-by-side arc segments at the top and bottom with just 1 arc in each of those spots.


So Burr you were definitely on the right track! :)


- Michael