Loft Bug, view bug

 From:  Michael Gibson
2688.4 In reply to 2688.1 
Hi Val, some notes on the Loft thing,

> Hello, I am getting some weird issues with Loft. When I use a cylinder
> or a circle to Boolean a whole in a surface, and then select the edges
> of the whole to Loft a surface.

Actually the best way to do this is to make sure your base object is a solid first, before you do the boolean.

When you boolean a solid with a circle as the cutter, it will automatically leave behind the "side walls" of the extrusion of the circle so you don't have to do any other lofting steps after that if you work starting with a solid.

If you are working on a surface, then it will cut the surface and you will have a hole, but like you saw here it will require some extra work to fill in the side parts.

Also you will get a much more complex "side wall" surface if you try to Loft the edges that were produced by a boolean intersection command, since those edges are the result of a surface/surface intersection and will generally be a lot more dense and complex than a simple cylinder surface. So it's best really to avoid doing that process anyway.

Just a quick illustration of the more optimal method - if I start with a solid box here:

Then when I do a boolean difference with the circle as the cutting object, I get this result:

Then there is no additional work to do at all, it's all done because when booleaning a solid, MoI is able to figure out how to combine the volumes of the original shape with the extrusion of the cutting curve, to leave the side walls in place.

When cutting an open surface rather than a solid, it is not really easy for MoI to have as good of an understanding of which regions of the side pieces are supposed to be kept and which are not.

So if you kind of keep your base object tuned up to be a solid you can then take advantage of some of the solid modeling steps to save some steps in situations like this.

Otherwise, if you are working on surfaces only, instead of doing the boolean with the circle and then trying to loft between the open edges, it is generally a better idea to extrude the circle into a cylinder, then trim the cylinder and the main object with one another to make all the pieces which you then join together. That will produce more simple final geometry since the extruded surface is more simple than a loft between 2 possibly heavy edges that were produced by surface/surface intersection.

- Michael