How do I mean a semi-circle?


So i’ve been trying to make a semi-circle where I have drawn a red circle. I have tried a lot of different things but nothing gives me the result I want. Adding a subdivsion surface makes everything looks weird so I can use that. You got any ideas? I am trying to model a Tiger tank turret

did you try knife project ?

happy bl

I did try that but I can’t get it to be a perfect half-circle when I use the knife

may be with a Boolean try with full circle then remove parts you don’t need!

can you show final result as pic or photo you want

happy bl

I also tried that but it didnt work out to well, I could try again though if I might have done something wrong

here is the picture of what I want to achieve

A method you could use:

Fill the hole back up, and maintain the clean shape and topology. Duplicate this, and make it a new object. You should now have 2 of the same object. Shrink wrap one to the other, and on the shrink wrapped item, cut the whole out once again, and move the verticies to make the desired shape. Because it is shrink wrapped to a base mesh, it should maintain it’s rounded shape without distorting or pinching.

Cut any wholes you need, and then simply apply the shrinkwrap modifier. You should be able to use subsurf aswell. (add subsurf with the shrinkwrap, but only apply shrinkwrap) Just make sure things that need to be sharp have edge loops.

Does that make sense?

can you show a photo for this hole so we an better understand how it looks like

happy bl

Not sure what hole you mean? the one I made in blender or the one I am trying to copy from the picture I posted in the comments?

I will have a go at this. i understand what you mean, so I will try and see if I can get it to work.

Thanks for the tip :slight_smile: will get back to you if it didn’t work or if there is something I don’t understand


With a Boolean, you can arrive at a satisfactory result …:+1:

Comming here flexing are you haha :wink: but yeah that is excatly what I am trying to achieve. I did try to use Boolean but didn’t get it to your result, is there by any chance that you could explain how you did or maybe show it? :slight_smile:

Not much to it. Model the major forms and forms for the cutouts with enough resolution and you get that. The shown structure is not suitable for subdivision surfaces. It also contains concave and non-planar n-gons, UV unwrap is unlikely to give good results, and will likely have trouble with shading.

But it does contain the forms, which can be used to build the required structure. Could start with a separate object, and use face snapping, shrinkwrap modifier, or other retopology tools to get the mesh to adhere on the existing forms.

This sorta structure for subdivision

This can be achieved without boolean. First, fill your hole back in. (Don’t worry, we’ll make it a hole later, this will just make it easier to model.) Please take notice! It will look odd until you get to the end, but the results will be what you’re looking for.


Next, add a couple of loop cuts to that sloped incline, so we have more vertices to work with. Since it’s conical, rather than a more spherical shape, it won’t change the result when you eventually add a subsurface. You should now have four rows of squares instead of two in your target section.


The next part’s a little harder to explain in words, but I hope the image will elucidate. You’re going to want to rearrange the vertices until you get your crescent shape. The easiest way to maintain your topology is to only move the vertices along the object’s surface, which you can do by selecting the vertex in question and hitting ‘g’ twice. I added one loopcut on the end, just to keep the topology clean, but you may need to add a few more for yours. The initial four was just an example, feel free to add as many as you feel comfortable, it won’t ruin the topology. In addition, I also cut a line across the surface at the bottom of the crescent, because it looked a bit messy without it; you can do this by selecting two vertices on either side of the wide space and then hitting ‘j’. It will make the shortest line possible while retaining topology.

What I changed:

The crescent:

Okay, we have our crescent; it’s not the prettiest shape at the ball, but it will do for demonstration purposes. Now it’s time to inset your faces. With your crescent selected, hit ‘i’, then slide it in to a small amount. Do this one more time, so you have a neat little border. This will make a holding edge for the hole. Since this is a demonstration, I didn’t adjust the vertices, but you may want to if it makes it look messy. It’s the space of the border that’s important.

Now it’s time to make it look more like a hole! Select the inner faces and extrude into the barrel for as thick as the outer shell is.

In the below picture, You’ll only have the innermost selected; I merely selected more to make the extrusion more clear.

Back in your side view, deselect the inner vertices until only the outer ring is selected.
Orbit around a little to make sure that’s all you have selected, and you have the full ring. This is important for clean topology.


Leave it a little orbited to make this next step a little easier. Bevel this edge (CTRL+b) but only a small amount. This is going to make a holding edge for the bottom of your hole.

Now all you have to do is delete the inner vertices and add your modifiers and materials!

Dude thanks so much for making a little tutorial. This is what I ended ut with, I believe this is the result should look like if I did everything correct?

No problem! It’s easy to forget even the little things had to be learned at some point.
It looks good to me! If you want to sharpen the end of your barrel, either add another edgeloop really close to the one at the end, or crease it with CTRL+e! Moving the mouse up and down will increase and decrease the strength, then another click confirms.

Forms need tweaking. Can’t say about the structure since you’re not showing it.

Way too high subdivision levels. Usual target level is 2, sometimes 3, rarely 4, and never 5 or 6 . Use lower level and smooth shading, unless the model is for 3D printing, and even then a lower level subdivision is likely to be enough.