Why doesn't Intersect Faces work consistently?


I used I.F. for this model and it worked well on the red axis but can’t get it to work on the remaining green axis.

Select both groups, IF Selection, explode both groups, delete unwanted portions, worked once but not twice?

middle corbel back 4.skp (2.0 MB)


Not sure where you are going astray…I dragged a selection box around the top of the model (getting the parts for which intersect is of interest) then did IF->with selection. Then I cleaned up the extra stuff. I needed to redraw one edge on the outer face to get SketchUp to recognize that the countersink should have formed a new inner face, but after that everything cleaned up fine.


Thanks @slbaumgartner, that worked for me too. IF is very powerful but not too intuitive (for me any way).

The first one worked just fine as I described, but not the second one, don’t know why (don’t care either) using the Selection tool seems to be the best way to do this.



The thing that causes people the most confusion is that Intersect Faces With always puts the new geometry into the currently open edit context (the whole model, a group, or a component), regardless of whether you choose “with selection”, “with context” or “with model”. These choices affect what is considered for intersection without changing where the results will go!


SketchUp may be punishing you for working on a model that isn’t as accurate as you may think.
You think that the model should act equally for both directions but the base of the face “on” the red/blue plane isn’t on the red axis, nor its top. But worse, it isn’t vertical. The other perpendicular face (in the green direction is vertical. The front face of your object isn’t vertical either. These “small” errors and the sequence of intersecting (either green direction object first or red first) might be the cause of differences in results that you noticed.
Zoom in (in Parallel Projection + Top View + X-Ray) in your model on the marked red and green spots that you see in this image:


@Wo3Dan you must be right. Don’t know how that got “so out of whack”, I tried it again with a new model and it worked just fine, thanks for the info.


This post is very clear and helpful to me. Thank You.