Lines drawn on any axis will not draw on face of object

When I draw a line on any axis (green, red, etc.) onto a face, the line doesn’t connect with the face. I’ve included an image to help explain this: When I draw a line on a face, to split it in half and push/pull one of the halves, I can’t because the line hasn’t been drawn on the face and therefore hasn’t split it in half. I can’t tell if this is because the building model I created is somehow not straight or aligned with the axes? Any advice? Thanks.

First thing would be to upload your .skp file so we can see exactly what you’ve got. Most commonly things like this are due to faces being off axis. Impossible for us to tell from only your screen shot.

Chamber Building .skp (179.9 KB) Sorry about that, here it is.

OK. So your model shows what I suggested. The side of the building is not parallel to the red axis so drawing a line that is on axis wouldn’t intersect at both ends. If it was on axis the Y values would all be the same.

Also note the hidden geometry triangulating the surface. These are required to create the faces due to the lack of planarity of the outer edges of the wall.

Sweet, thank you. Looks like this did the trick!

Here’s another thing you might find useful.

I have a pre-set scene in my default template that colours lines according to the axes they are parallel to. If lines show up as green, red, or blue, they are on axis. If not, they show up as black. So a quick look at a model in that scene can often tell you right away if something is wrong.

Here’s what your model looks like:

Just a heads up on that. The colour by axis tolerance is set somewhat loose, so even correctly coloured edges can be slightly out .
So the black edges could well be planar without being on axis and the coloured ones may well be ‘on axis’ without being planar.
Just saying it’s not a guarantee of flat faces.


I did away with that scene and set up a toggle shortcut using AutoHotKey to display colour by axes (and thicker profiles at the same time) so that I can check this at any instant of my modelling

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I didn’t know that. So how useful is Colour by Axis in that case?

Have a read here. Just one of many threads on the topic.

I’m surprised I hadn’t seen any of those threads before. Anyway, I know now so thanks for pointing it out.

I have that scene set thanks to @mikebrightman’s book. I wonder if he realizes that it is not as useful as it appears?

Simon, I think it can be useful but I wouldn’t count on it exclusively for troubleshooting planarity. That’s why I didn’t even both to show that in my post and chose to show the coordinates of points, instead. Although a little more tedious to use for checking or showing the problem, it can pick up smaller errors it you choose the units and display precision correctly.

Yes, I probably should have used the word “accurate” instead of “useful”.

Well, it is useful when modeling, i.e. creating new edges, showing a new edge will be on axis. Not so much for checking existing edges. For that it appears to be too rough due to its tolerance on existing geometry.

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