# Using "Intersect faces with model" to join 2x4s that are cutting through the plane of a flat surface. Then I want to trim the excess

Trying to use the “Intersect faces with model” function to design a truss system. I need to quickly join 2x4s that are cutting through each other at strange angles but all are in a 2D plane. Specifically I’m using push-pull to lengthen or shorten studs and where they join, I just push-pull one beyond the intersection. Then trim the excess and have a perfect joint. If the 2x4s are 2 different components or groups, how do I get them to interact? Paste-in-place one component inside the other? Very confusing. I know it’s simple. I tried tutorials. Many thanks in advance. Running Sketchup Pro- 21.1.331 iMac. Here’s my file–
Parallel Chord Truss Exercise.skp (152.8 KB)

Intersect Faces does just that and puts edges where the faces cross in the current context. If you open a group or component for editing before running Intersect Faces, the edges will be placed on the faces inside that object. Note there will be no face created only edges. If you erase the geometry beyond the intersection you’ll have a hole. If you copy the intersecting faces into the object before running Intersect and erasing the waste, you’ll wind up leaving some of the intersecting face behind as a skin over the opening.

Frankly if I needed to do what you are trying to do, I would make sure my objects are solids and use the Solid Tools to trim one with the other. And for something like this where you are surely going to have multiples, I would make components instead of groups and use either Eneroth Solid Tools or Bool Tools 2 to do the trimming because they respect component properties.

Thanks very much DaveR. Well I guess the first thing I need to learn is the difference between a solid and a hollow object. How can I tell if an object is solid? I’m assuming if I make a shape with a surface and push-pull it to 3D, it’s automatically solid. But if I borrow an object from 3D Warehouse, how do i know it’s solid? Your suggestion to use a plugin is a good one but I should probably try and do this with the solid tools that are already in the program and understand those first, right? Also a good idea to make each different stud in this truss a component…

All objects in SketchUp will be hollow because SketchUp is a face modeler. To be considered a solid, though, every edge in the object must be shared by exactly two faces. So no stray edges, no holes, and no internal faces. You can tell if your group or component is solid by selecting it and looking at Entity Info.

Probably, once you make a group or component to contain the geometry. As long as it meets the requirements above.

You don’t unless you select it and look at Entity Info. For something like a piece of construction lumber I wouldn’t even consider the 3D Warehouse. It’s such a dead simple thing to model from scratch it isn’t worth the time to search for such a component.

FWIW, solid groups/components generally tend to be cleaner and easier to work with so it’s worth making them solid even if you aren’t using things like the Solid Tools.

It is a good idea to learn to use the native tools first. The reason I suggested Eneroth Solid Tools instead of the native ones is that the native ones convert components to groups when they modify them. If you watch in my gif above, the king post gets trimmed in all of the trusses at the same time. That’s because the king post is a component and because I’m using Eneroth Solid Tools instead of the native Solid Tools to do the trimming.

I think so. Makes edits to the trusses much easier later. For example if you need to change the length of the chord, you can edit one instance of the component and all of them will show the same change. You could also make a nested component of all the truss components and copy that . Then other changes like maybe changing the height of the chord and the length of the king post will happen in all the copies saving you a ton of editing work.

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