Trying to create a face, but I think I am having coplaner line issues


roof.skp (157.1 KB)

The end product of what I’m making is a dome roof out of steel. It will be cut on a cnc plasma cutter and then the 8 rolled pie sections will be stitched welded to form the dome in the end. Before I get there I need to get a pattern from the wedge, and that’s where the unwrap and flatten extension comes in. And here is where I’ve hit my roadblock.

I’ve redrawn this several times and I can’t figure out where I am going wrong. The wedge needs to be a face so that the unwrap and flatten extension will create the outline so that I can cut this out. I’m assuming that it’s a coplaner problem, but I cannot for the life of me figure it out. When I drew up the dome I made sure I got the green dot that showed me that everything is connected. If someone can shed some light on this mystery I would greatly appreciate it.


The roof you are drawing is not planar/flat, it is arced, hence it can not be covered by a single face in SketchUp. It will need to consist of a bunch of trapezoidal faces. One (tedious) way to create them is to stitch together the corresponding endpoints of segments on the two arcs:

A faster way might be to draw a profile, follow-me it along an arc, and then erase the extra geometry inside the roof.


If you just want eight flat wedges that will curve to cover the framework, the framework has to be made from an octagon, not a 184-sided polygon. If I understand you, you want the one on the right, but you’re set to construct the one on the left.



Thanks for the reply guys! I think the trapezoids might be what i need to do to fix this. I’m going to have to give it a go.

Gully, I actually want the one on the left, but I’m having to break it up in those sections so that I can cut them out of the steel on our cnc plasma cutter, roll the pieces, and then stitch weld them together. This will give me a really smooth form in the end.


Tigs Extrusion tools will sort the shape for you, then you unfold it.


Thanks for the heads up. After following the dialogs, I’m trying to figure out what you did to just have the shaded face. The unwrap and unfolding extension is having trouble with all of the lines. Any suggestions?


Use spider in the center , make all the segments flat, they may have to cut at dihedral angle. There was a recent post on how to calculate how many panels needed to make for a small error.


here’s a good link for making domes from sheet metal…
[ link to spheres here, domes in sidebar][1]
if yours is really only 2’ with a 6" draw, I would look at base-ing it on a geodesic form, and press or panel beat the initial curvature into each before welding…
in the past I have had similar size domes metal spun and avoided all welding…


I just used the soften edged dialog.
It doesn’t remove them just makes them smooth, so it’s up to you how you unfold them.
Never used the Unfold and Flatten Plugin,but from what I have read it can be a bit hit and miss, have used flattery, it will do it but not automatically, I believe you will need to click all those little faces in the right order to get it flat.


" Surfaces about which a thin sheet of flexible material can be wrapped smoothly are said to be developable: those include objects made up of planes and single curve surfaces. Warped and double curved surfaces are not developable aka base ball. They will rely on the ductility and plaiability of the used material .
Approach all boils donwn to cost, fidelity you are willing to trade off. Item is small so spinning sphere etc my be ok it is you cal.l