Mirroring 2d shapes gives me "invalid selection"


I am trying to draw 2d shapes, mirror them then use them to then extrude with.

I can mirror basic shapes like squares and rectangles.

Whenever I try to mirror anything I have made by connecting a few shapes (like a rectangle and a circle to get a rectangle with one curved end) I get “invalid selection” when I select the edge I want to mirror from.

I’ve since been attempting to exactly copy a few videos of people mirroring stuff and despite trying to recreate exactly what they have done I am still getting “invalid selection”

Help appreciated I’m currently stuck unable to progress unless I do very tedious and careful redrawing of everything I want to mirror.

Hi Liketrains,
it is alittle hard to help you without seeing the geometry you are working with.
Basically all volume-modelling (Solid) CAD-software have issues with so called zero-geometry or zero-thickness.
That means if you have a shape with a sharp vertex at the line of revolution - that relults in invalid geometry.
Please help me to help you with some screenshots.
Cheers Matt

In the attached image, I have drawn a rectangle, an arc and then removed some lines to create an irregular shape.

I can mirror the rectangle but I cannot always mirror the end product after Ive added a curve to it.

Checking again this behaviour seems to be inconsistent - drawing the shape by itself for the above screenshot just worked but drawing it in contact with the edge of the shape I want to extrude through gave me the same error message.

Drawing it in contact with the shape then moving it up a little then using the mirror tool also worked - looks like I have a solution of sorts there it’s just going to require more steps.