Make a 180mm round hole in drywall...

[MalZon]

...without a hole saw?

I've realized that buying a hole saw around 180mm isn't worth it, as spending around a thousand kronor for one hole isn't justified for a hobby woodworker.

I'm going to make a hole in a plasterboard for a 160mm spiral duct, so 180mm should work, but how do you make a nice hole without a hole saw? It's my first time doing this.
For the OSB, I used a jigsaw. It worked, but the hole didn't turn out very nice. And with plasterboard, there's a bit of pressure for it to turn out well

 

[Raka]

Draw how the hole should be on the drywall, then just start drilling to make holes at regular intervals around it. Then take the drywall knife and cut from hole to hole until you are through.

 

[Johan Gunverth]

Draw a circle with a pencil, saw just inside and then rasp off the remaining gypsum. A rasp with a smooth and half-round side is always good to have.