Advice on how to build these surfaces better and smoother

Hey everybody, need some advice on a better way to construct these surfaces and blend them a lot smoother. What I got here is a kinda replica of a gun/cannon used on a movie prop. The part that’s giving me trouble is the plastic housing surrounding the gun. I initially made the top half first, then tried to make the bottom piece to match it and connect them together into one solid housing around the center of the gun. The left front side is the main problem area…I tried rebuilding the surrounding surfaces several times to match better @ the middle but just can’t get it smooth enough. Def not getting G2/Curvature like I really want. In the latest iteration, the bottom left area I created with XNurbs, it couldn’t pull it off either. Def not blaming the software, I’m sure it’s user error…that’s why I’m here. I’m hoping someone can give me some direction/ideas to pull it off. I’d appreciate any input. I’m thinking it could also be done by using Sub-D, but I’ve literally just started messing around with Sub-D stuff in the last night or so. Again, I’d appreciate any advice/input, thx so much.

Attached are some pics below and the Rhino file:

And the Rhino File: BasicCannonShell.3dm (2.0 MB)

Hello - the first thing to do is make sure the analysis mesh is accurate - in Zebra, click AdjustMesh and change this setting in the detailed controls:


I had played with those settings awhile back and forgot I reset it back to default. I believe it was taxing my laptop quite abit. I’ll try it out at 5000 and see how much a difference it makes, thx.

Hello - it looks to me like, while XNurbs seems to have really done a pretty good job here, you could help it more by cleaning up these curves -

See how you have sudden, or instant (tangent) changes in curvature right where you are detecting the problem with Zebra? Also on the nose - I think I’d try to find shapes that come across the centerline with similar curvature & acceleration.


Thx Pascal, I don’t know how I missed the tangent CV’s, I could’ve sworn I matched all the bottom CV’s at G2. I’ll work on that and see what I get, thx. Btw…when using Sub-D (just started using it this wk) …is there a command to “straighten/align faces &edges,” ie… to make em look less sloppy, alignment-wise? T-splines in Fusion 360 has a similar command called Straighten, useful for getting the faces to maintain vertical/horizontal alignment. I don’t use F360 anymore, but just wondered if there was something like that for use with Sub-D’s. Anyways, thx for replying.

Hello - Smooth, on the control points may help, as well as AlignGrips.


Hi Pascal, I tried and tried to get these surfaces to work out, I don’t know why I can’t get it. I’d really appreciate it if you’d show me how u would go about creating it. I can make either top or bottom surfaces (by themselves) no problem but can’t get a decent blend between them. I won’t lie, I’m pretty much embarrassed right now, it should be simple. I tried looking for similar shapes online to help but found nothing close. I’d really be grateful, thx.

Hello - I am not sure I know where we are any more - can you post a file with just the surfaces and curves we’re dealing with? It may simply be hard… One difficulty with xNurbs, to my mind, is that the surface arrangement is not necessarily all that conducive to building new ‘regular’ surfaces - at the edges.


Hey Pascal, I’ll send a revised version of it, with a couple pics of the real object, thx so much.