Issues with Subdivision Surface Modifier

So. I’m working on a plasma pistol, and when I go to subdivision subsurface it, it creates an indent as if it has been hacked at with an axe or machete at the front of the back part of the iron sights. karmagun.blend (467 KB)

It’s because you’ve been trying to cut corners with your modelling.

The subsurf modifier worst best with quads. If you use triangles or in your case faces with > 4 sides expect to get artifacts. Remake your model with quads where you get the errors

Subdivision surface, subsurf in short. Subsurface:

The structure isn’t suitable for subdivision surface

The modifier is set to simple, which subdivides all faces without deforming it. With that it puts 4x more geometry on each subdivision level (with quadrilateral faces), optimally without changing the surface at all. That’s added geometry that doesn’t do anything to improve the form so it’s useless.

The modifier is set to be visible in edit mode, and also on the control cage. When using Catmull-Clark to refine the forms by adding more geometry and approximating the surface again, showing the subdivision on the control cage doesn’t show the actual vertex positions and if not before, building a model structure with that on you eventually end up with a mess because of that.

Subdivisions are predictable with quadrilateral face structure. Yours has n-gons and triangles that make a different pattern when subdivided
There are also severely non-planar polygons
and concave polygons
and there are non-manifold errors because of two interior faces

The use of subdivision surfaces is planned, including the subdivision level. The structure that is modeled is the control cage for the subdivided model, it’s not just a modifier that when added just somehow makes the model better.

Subdivision surface introduction
and couple of simple examples of structure flows for subdivision

Okay. Thank you for the info, I’ll try redoing the broken chunks of it with it in mind.