# Correct way of subtracting a plane from a bigger plane

I have a pretty general question. I have encountered this problem several times now (I'm a beginner, by the way). In the case I had two diferent planes (just edges, not faces yet) in the same XZ coordinates and wanted to create a face for the bigger element, but leaving the smallest one blank, as it was a hole on the biggest one, how would you proceed? Which is the easiest or fastest way to do it? I'm adding some screenshots. Thank you on advance!

Edit: Situation with knife project.

• Probably easiest to use Knife Project, but you'll need to Fill the large plane first and move the octagon forward slightly in the Y direction. Then go to front view (numpad 1). With the large plane selected go into Edit mode, CTRL-click the octagon then Mesh > Knife Project and delete the new face from your large plane. There's a quick Blender Secrets video here Sep 29, 2022 at 11:39
• @JohnEason No no, it's one mesh in Edit Mode and he starts with only edges, no faces... I wouldn't use Knife Project then. Sep 29, 2022 at 11:45
• Ah mea culpa. I was thinking it was two objects (although you could seperate it into two... :^). In that case your answer is the best. Sep 29, 2022 at 15:13
• @Rant Well, no matter which version you use, creating faces between edges or using Knife Project, you will never get rid of all diagonal edges. If you only problem that they are not aligned with the axes, you could of course split the edges of the square and connect the inner circle only horizontally and vertically instead of diagonal. But nevertheless there will stay edges, because a hole cannot be surrounded by a single polygon without connection from the inner border to the outer border. Sep 29, 2022 at 21:26
• Your objects need to be viewed "head on" (i.e: numpad 1, 3, or 7) when you use knife project or the cut will be offset as you've found. This is the Blender manual entry. With regard to your other question about leaving invisible faces, it's a good idea to delete them, partly to keep the number of faces as low as possible, and partly because they can cause distortion and shading issues particularly when using a mirror modifier. Sep 30, 2022 at 9:25

I'd say the simplest way is this, when you're in Edit Mode with Edge Select like in your top screenshot:

1. Select the top edge of the square and the two top edges of the circle. Press F to fill them.

1. Now do the same for the bottom three edges.

1. Repeat this for the left three edges and again for the right three edges. You don't need to select the new diagonal lines for that.

Of course you could do this by creating two faces instead of one, but I think the four faces version above gives better, cleaner geometry:

1. Select the top and side edges and press F to fill them.

1. Then select the bottom edges and press F again.