Making Clean Hole in Side of Cylinder

I’ve run into a minor wall when it comes to cutting holes in things in Blender. I want to make a hole in the side of a cylinder, like a note hole on a flute, for instance. When I try, however, I get outward deformation, like this:

Those screenshots were taken of an 8-sided cylinder using 3 layers of subsurf. The hole was simply where I deleted a single face from the side. I’ve tried creasing and sharpening the edge with an edge split modifier and Mark Sharp, but neither seem to stop the deformation. Any movement of the adjacent vertices or edges just results in more deformation. I just want the roundness of the cylinder to continue uninterrupted, just with a hole in it. Does anyone know how to do this?

Use the Boolean modifier. You can make a clean cut hole that way.

First scale the verticies that are farthest right and left on the circle to two of the edges on the side of the cylinder. This doesn’t have to be exact. Then snap each of the verticies of the circle to a corresponding edge on the cylinder. Then subdivide the edges of the circle as needed to where there is a vertex for each edge of the circle so you can make faces with the top and bottom edges of the cylinder and circle. Add a loop cut to the center of the circle using Alt + R. Delete the edges that are intersecting the circle. Then make faces with the edges from the top of the circle and the cylinder and then do the same with the bottom. If you’ve done it the way I did it there should be four sets of four verticies with only one vertex touching the circle instead of two. Make faces out of these too.

This should give you the result you are looking for if done properly. If this half assed explanation is too hard to follow please let me know and I will post a better one sometime tomorrow.

I don’t think I quite follow your explanation. To clarify some things, I uploaded some images that show what I’m talking about in edit mode as well:

I hope these images clarify my problem.

I think you’ve probably hit upon a quirk in how the cylinder smoothing works as the 2 problem areas are at the beginning and ending cylinder edges but the one between those 2 is smooth. I think as suggested earlier to work around you will have to use the boolean modifier (at least until a later version of Blender. Ask one of the Blender devs if this is a bug or a feature)

At any rate, as someone that is new to modeling (my 5th day) I would like to know how to make this 8 sided cylinder so smooth (as mine are anything but that).

Trying again, my post seemed to have disappeared: The cylinder is smooth because of the subsurf modifier. I just tried this by adding an 8 sided cylinder and then a sub surf modifier at level 3 or 4. It makes the cylinder appear very smooth, but if you tab into edit mode you can see the original 8 faces as a “cage.” As for making a smooth, circular hoke, yes a Boolean worked fine for me.

Im going to try to upload an image


Very nice, I’ll have to read what subsurface modifiers are when I’m ready for that. Thanks.

Glad i could help. Subsurf is a very useful modifier.

This is standard for a subdivision surface. Catmull-Clark subdivision smooths a mesh by pulling vertices toward the centers of adjoining faces. When one of those faces is removed the vertices are no longer pulled that direction.

There are two workarounds I’m familiar with. Either, use a boolean modifier to cut the hole after the subdivide modifier. This is the easiest to set up and modify but creates a poor mesh with lots of triangles and normal artifacts. Or, apply the subdivide modifier and model the hole in the subdivided mesh. This will give the best results, but as I said, it isn’t as easy to do, or to change later.

So you’re saying that if I want to maintain good topology I’ll need to apply the subsurf modifier before I can create the smooth hole? I was hoping to be able to keep the subsurf up as a modifier without applying it while preserving topology, but I guess I can’t have my cake and eat it too.

Thank you for the help!

Also skygoat, if you do what wms3 said for making a smooth cylinder, make sure you extrude both ends at least once, otherwise you’ll end up with an egg shape when you go to apply the subsurf modifier. And in Object Mode, select the cylinder and click Smooth under the toolbar to the left (If the toolbar isn’t showing, press T), otherwise you’ll need 5 or 6 layers of subsurf to make it actually appear smooth.

I’m not an expert, but I’d say it’s pretty hard to cut a hole that subdivides nicely without at least 10 sides to the cylinder.
Here’s some quick variants… they can all be tweaked to minimise bumpyness, but you get the idea. I think the leftmost one is pretty hard to tweak into a good result… I wouldn’t use that.

And a rough outline of how you can create the curved holes, if it makes any sense. “Snap to face from an ortographic view”, basically. I prefer toggling Snap with ctrl rather than activating the icon.

If you want to resize the hole when it’s already connected… just ignore the connecting faces, move the circle up and snap it to the clean cylinder, and move it back down again. Looks ugly, but works fine:)

With the examples given by encn I need to amend my answer. When I said you need to apply the subdivision, I should have said you need a cylinder with more than eight sides, then model the hole. Simply deleting faces will not give the results you’re looking for.

EDIT: Also it is not necessary that you extrude the cylinder to maintain sharpness at the top and bottom edges. You can put an edge split modifier above the subdivision modifier and set it to edge angle and a split angle of about 80 degrees.

Ok, I think I see what you’re saying. I’ll play around with it and try adding more sides to the cylinder. Thank you so much for those images, encn, they help tremendously! And you’re right BentFX, you can do it that way too. I was just mentioning the first way that came to my mind to prevent having an egg mysteriously appearing where he thought a cylinder was supposed to go. :wink: