As depicted, I need to trim the face of the tray (curved geometry) to be parallel with the angled face. The cutting plane and the tray are components. When I select both and use “intersect with selection”, I get cut lines on the tray. But, the cut lines are on the “outside” of the tray component. How do I trim off the waste portion? Thanks for your help.
Intersect faces always puts the new edges in the current edit context, so in this case they are loose in the model. You could select them, cut, open the component, and paste in place.
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It should not. You are missing something.
- you’ve erased an edge or more that makes up the tray surface. OR
- the top of the tray was not completely cut and removing edges beyond the cut face erased the surface
It may be that you were too close to the end of the object and that messed with a clean cut. You could pull the end of the tray further past the plane you wish to cut.
Often using Show Hidden Geometry helps in working with smoothed surface to either run operations or analyze a problem. Hiding the smoothed edges again is good to select surfaces you’ve cut.
Still having “Intersect With Selection” problems. Managed to trim the insulation, but the vent (top and bottom) produce missing surfaces. Here is the model with the cutting plane and insulation and vent extended past rafter faces ( thanks @pbacot ). Maybe there is an extension that would quickly trim. Thanks for your help.
Intersect.skp (686.0 KB)
I was thinking of “intersect” for the vent. Usually do it, one component at time. Anyway for the insulation, since it is a simple form, intersect isn’t the simple way to do it. You push pull to the nearest edge, then move the other edge to meet the location you want it.
Intersect should work the way discussed above for the vent. For some reason it didn’t work for you, so I suggested extending the shape to get a clean area to cut.
So you copy your grouped face (or just “cut” it) and PASTE IN PLACE inside the vent component. You EXPLODE the face group and select the face, INTERSECT FACES, WITH CONTEXT. RIGHT TO LEFT SELECT the part of the vent you don’t want (don’t select any of the cut edges) DELETE. RIGHT TO LEFT SELECT some of the rectangle sticking up (don’t touch the vent), DELETE. ERASE any edges of the rectangle that remain. (there are faster selection/ delete methods, but this works OK here)
The vent wasn’t a closed shape. You need to add edges at the ends of the cut, either before you delete the cutting rectangle face or after, if you want a face at the end of the vent.
See the dark edges and a missing edge between the top and bottom outlines.
Add guides to accurately PUSHPULL the insulation to the bottom face intersection to the rafter plumb cut and to MOVE the top edge to top position.
You just have to move from the endpoint of the edge. The cursor just snapped to where it was at the beginning of the recording. You don’t need to run the cursor along the edge.
To correct this, I selected the front profile, used Push/Pull and extruded to length. This gave me a solid. Using the cutting plane, I then pasted-in-place the angled cut profile. To cut the waste section, using a crossing window, I can select the entire waste section (top image). But, when I cut, it removes geometry from the rest of the object (bottom image). Tried using solid tools, but it requires two solids. Feel like I’m making this more difficult than it has to be. 
Any suggestions?
Do not delete the new edges that form the cut face of the object. Deleting those edges causes the connected faces to be deleted.
Ok, but how do I remove just the waste section without affecting the rest of the geometry?
Ok, hate to answer my own question, but …
I gave the cutting plane some thickness (1/64"), created a solid. Now, I have two solids. Then use the “Trim” tool (Solid Tools). But, the order of selection is critical. Select the cutting plane as solid 1, then the vent as solid 2. Finally, move the cutting plane away, then window select the waste portion, delete, and you get this (no messy editing):
The only downside, is when using the native solid tools, the components get converted to groups. To avoid this, use Eneroth’s Solid Tools extension.
This really should not be so complicated, but it is. Or, maybe there is a simpler solution? For now, this works, using only SU native tools. 
I confess that I have not read all replies in detail, so the following may not make sense depending on exactly how the intersection geometry was generated. Are there are edges shared between the wanted section and the waste section? If so, don’t delete them. Only delete the edges that are purely part of the waste section, not part of the wanted section (e.g., edges that project beyond the intersection/cutting plane). You might have to select such edges one-by-one, or perhaps a careful selection box will get many of them together.
Keep in mind that a left-to-right selection box only selects entities that are entirely contained within the box, whereas a right-to-left selection selects all entities which are visible in the box. Use whichever form might be most suitable.
You made it work, that’s the main thing!
I made my suggestion, the whole procedure. Fixing the missing face was part of that process, just add the edges that were needed to make the face. You can make solids if you want. That’s another issue, but they are not needed to do what you asked: to cut the material at the vertical angle.
Simple: I would not cut it like this. In reality no one ever will. I’d just extend the vent up and leave it at the top. Maybe you want that vertical slice with all the faces to demonstrate in some graphic for apprentices, I don’t know. But it doesn’t have to do with construction practices IMO.
It’s sometimes easier to keep components intact as possible without a lot of operations that will mess with their geometry. The vents are always the same, some are longer than others. They don’t have to be sliced to the angle of the roof. Just make it longer. Also, as I said, I wouldn’t use “Intersect” on the insulation. it is such a simple shape to adjust with the move tool.
(I was just thinking of this, making a metal window frame for my own model. I was fussing with follow me to run it around the window, and the complexity of the shape was making subsequent modifications really difficult. I went back to just using extrusions to make each side of the frame, because that is how they are fabricated anyway–they don’t run “follow-me” in the factory, and it just complicates my modeling in this case. Now my extrusions don’t have to be messed with so much at every joint.)
Selecting the waste to remove. I explained that best I could: right to left selection- but don’t touch anything you want to keep such as the cut face edges. Then catch any leftovers with eraser tool. It goes quickly once you’ve done it a few times.
Thanks again for all your help. It was all your suggestions/comments that led me to the final solution, Solid Tools. I just found this approach to be less problematic, and I favor using native tools.
And, I fully agree with you about what happens on the job site. No tradesman I know, would ever think of cutting bevels on plastic baffle vents. I just think, that having a detailed drawing, adds a little professionalism to the construction drawing set. As you point out, there is a cost to this kind of complexity.
And, I found yet another solution from @Box, even simpler.
You can check out the details on another thread: