Intersect Faces Mystery

I am attempting to push/pull a fenestration shape through a bay wall. Push/Pulling the shape works on one wall, but not the similar adjacent wall. I’ve redrawn the walls, I’ve drawn the shape to push/pull, I’ve pushed the shape through the wall and then intersected faces but nothing works. I am not able to get a separate face on the highlighted surface shown below. It works on one wall but not the other.
Does anyone know how I may cut a shape into this surface?


Share your model and I’m sure one of us can find the problem.

The file was too big so I saved the example part as a separate file.

Intersect Face Example.skp (173.9 KB)

Much appreciated!

The edges that seem to trace the triangle on the front are actually a tiny amount behind it. The simplest way to detect this is to orbit around the model and see them come and go depending on where you view them from. I’m not sure how you got them that way - perhaps stopped a pushpull a bit behind the front face by not waiting for an inference to it?

At this point, because the distance behind the front face is so small, it’s a bit messy to clean it up. But here’s one way:

  • open the group for edit
  • redraw the bottom edge on the back so that the triangular face there forms again.
  • activate pushpull and press alt (? check the message in the status bar for which key to press for “Toggle Create new starting face” on Windows. I’m on Mac)
  • pushpull the back triangle all the way through the front face and past it a bit (with create new starting face on, this will be possible)
  • select all the relevant faces,right-click and Intersect faces with selection.
  • erase the extra edges where the extrusion goes through the front.
  • you may have to redraw an edge on the bottom to restore a face that was lost
  • orient faces to fix the visible back faces

Thanks for your help on this. Drawing cleanly is easier said than done!

You might find it helpful to go to Window>Model Info>Units and uncheck Enable length snapping.
Also, increase display precision to maximum.

I suppose that depends on one’s technique. My workflow is to either rely on SketchUp’s inferencing to match existing geometry, or to numerically enter the intended exact dimension. I never just drag something to an eyeballed location. I’m not saying you do either, but for me the combination of inferencing and numeric input yields a precise model.

One does sometimes have to be careful with SketchUp’s approximated (segmented) curves. for example, I generally use the Circle Intersect extension from @slbaumgartner to make arcs and edges intersect at precise radial distances, rather than run an edge through the middle of a SketchUp-generated arc segment (which places the intersection at an inaccurate radius). If an approximated intersection is created and then used for new derived geometry, the original inaccuracy will compound and propagate.

Actually, Circle Intersect is mine, though @TIG’s True Tangents has some similar abilities.

Oops, I apologize for not remembering your authorship. Thanks for the correction (I edited my post above), and for your Circle Intersect extension which is very handy!

What is display snapping. Is this something I will need elsewhere?
Also, I did not see a maximum option for display precision. Is this within the Units window also?

So, if I extend a line through the midpoint of an arc segment that is not really what is happening?
I will try the Circle Intersect extension.
Thanks much!

I went to the extension warehouse but was not able to find this extension:

SketchUp represents circles and circular arcs as a series of straight segments. It does not have true circles. Only the vertices of a SketchUp “circle” are actually on the mathematical circle it represents. So, if anything intersects a circle anywhere except at a vertex, the intersection is likewise not on the mathematical circle. My extension that @TDahl referenced creates guide point(s) at the true intersection point(s). It does not actually draw any geometry to the guide points because there are multiple possibilities of what you really wanted, particularly because there are usually two points of itersection. So, a small amount of manual drawing is usually needed afterward.

The extension is on SketchUcation, not in the Extension Warehouse.


To reinforce the general meaning of @slbaumgartner’s message and apply it to your specific question: the point of intersection of the line that passes through the midpoint of an arc segment will be a bit too close to the center of the arc. You can use the Tape Measure tool to check the distance from arc center to intersection point. It will be less than the radius of the arc, because the intersection falls inside of the arc’s true circular path.

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