topic Error when attempting to use thicken function in Fusion Design, Validate & Document Forum

Error when attempting to use thicken function

burdine_road — Wed, 26 Aug 2020 04:18:42 GMT

I have an air duct that I am trying to thicken by -3 mm. I altered an old design that I was able to successfully thicken by this amount. After the alterations for this new iteration of the design, it will no longer allow me to thicken the object by -3 mm (the negative amount allows me to keep the appropriate OD of the spout of the duct). It keeps giving me this error:

"Error: The operation would cause a large topology change.
Try adjusting the values or changing the input geometry."

The biggest difference between this uncooperative iteration and the previous one that was able to thicken is that I am using rails during the lofting process, but I don't think that is the cause of this. I've included the f3d file to help with finding the problem. After hours of researching and trying to get this to work, I'm finally resigning to the support forum. My frustration is very evident in my terrible work flow on this, so bear with me. I appreciate any help on this that you can offer, and am open to any other suggestions or tips that you would deem helpful.

Re: Error when attempting to use thicken function

laughingcreek — Thu, 27 Aug 2020 18:07:15 GMT

There are a number of problem areas here. The thing that is proabably casugin the thicken to fail is at location 1

index pic

close up of 1-

you can see the curvature of the nurbs edge is pretty bad, and the surface kinda rumples over here. This is caused when you loft over a sharp corner and have rails mid span on either side. you will have to develop a way to gain control here, probably by adding a rail from the corner. more on that later.

The curvature of this spline is pretty bad to, and will result in a poor surface-

This is caused by the large number of points on your spline. You want to have as few points as possible on fitpoint splines.

offsetting a fitpoint spline results in even worse curvature quality-

I think this is more a limitation of the offset tool in fusion. the work around is to extrude a surface from the original spline, and offset the surface. the curve quality of the new edge will be much better than that of the offset sketch curve. use the new edge of that for your loft.

did you intend for the edge around the rim to be flat? if so it should be formed with a different operation first. in this close up of location 2 you can see that trying to run the spline through 2 points that are planer results not in a straight line, but in a curve. same for lofting through these profiles. this could also be stopping the thicken from working-

Re: Error when attempting to use thicken function

laughingcreek — Thu, 27 Aug 2020 18:42:08 GMT

attached is an example approach that might work better for you. I personally would take this a step further and put fillets at the sharp corners before lofting and get that crease to fade out nicer

Re: Error when attempting to use thicken function

burdine_road — Wed, 02 Sep 2020 17:30:05 GMT

The curvature at the edges was definitely the problem. I didn't even know that the tool you used to view the curvature of the spline existed (i think it was called the curvature comb). That was a big game changer for fixing the issues. once the curvature issues were resolved, Fusion had no issues with lofting and thickening the model. I also studied that file you included in an attempt to better my work flow, and I ended up basically redoing the model using your example as a guide. I tried my best to make sense of what and why you did what you did and was able to get a pretty good result, even though I know that I still could have done a much better job. So thank you a ton for that, I appreciate you taking the extra time to do that.