How can I "cut" a diagonal across a model of 4X8 siding

Thank you all for your responses. I do just want to cut a corner off the 4X8 sheet. The cut is just a line from one side to a point on the top, not at the corner. I chose to download a model of the siding, not realizing the complexity involved. I could just use texture for this project. However, I also wanted to learn a technique to make such a cut. I have a similar problem with a roofing shingle model I downloaded. When I get to the edge of the roof, the shingle hands over and I would like to just cut it off. The use of a plane should work for this situation also.

Unfortunately, I haven’t been in a position to try your suggestions, but I can’t wait to try. Do I intersect the plane with the model while the model is in edit or can I just point to it and make the intersection?

Again, I really appreciate your time and expertise.

How you intersect depends on the context and what you want to achieve. you can intersect with Selection, with Model or with Context. They will give different results for different reasons. Basically If the roof shingle or siding etc is a group or component, then you need to intersect while in the group and intersect with Model, so that it is intersecting with something outside the group, ie; the cutting plane.
Here is a sphere being cut with this method, that I made for something else. You can see here I deliberately changed the angle of the cut so that it didn’t line up with the hidden geometry.

If the cutting lane is already in the same context, as in inside the group, then you can select the relevant faces and intersect Selection, this will give you the cut face in place also, but can be harder to remove the excess.
You can intersect two closed groups and it will give you the geometry of the intersecting edges outside both groups. You can then select and copy that geometry, open a group and paste in place and you have the cut that way.
So there are many ways to slice a cat, as they almost say.

I am obviously doing something wrong. I think I follow your great example, but when I delete the plane and then try to highlight the section to delete, the whole siding sheet is deleted. In other words, there is o intersection. I downloaded the model, made it a group, placed a plane where I wanted to make the cut, selected the intersection with the model, deleted the plane. I try to delete the piece that is not wanted, and the whole 4X8 sheet disappears. The only thing left is the line I drew marking the cut line. Where did I go wrong?

If you post your model, the helpful folks here can probably tell you exactly where you went wrong. But it is hard based only on words, which unfortunately always contain unstated assumptions or actions.

Did you make the plane a group? Did you select the plane and activate the intersection command “with model” as well?

In it’s most basic form you don’t need to make it be a group, that was was specif to one problem and might be more than necessary for you.
If the object you want to cut is raw geometry simply place the cutting plane though it, select all of it, right click and Intersect with Selection.

It’s possible that you have downloaded a Group and made it a group again, causing it to become a nested group …
So as mentioned above the model would help, at the very least a screen shot.

Thanks again. I will try to send the model as an attachment .skp file. I got it from 3D Warehouse by doing a search for “siding”. It is titled “T111 Siding” by Shedman. It is in the 2nd column, 3rd row. I think I messed up by not making the plane a group. Your examples are great, especially this one. Now, I don’t see any paperclip icon to attach the file.

There is a little upload Icon just above where you are typing your reply. The 7th icon across sort of a bar with an arrow pointing up. That’s the attachment.

If you mean this then it isn’t a group and you don’t need to make a group.
Just make a rectangle and put it where you want to cut, intersect and delete.

If you have got it from 3dWH it’s probably still a component instance in your model.
I also anticipate that you want to keep an uncut rectangular version too ?
If so insert an instance for the one you want to cut…
Select it - context-menu > make_unique.
Definition “xxxx” is joined by “xxxx#1” - a unique duplicate.
It is initially identical with its sibling…
If desired you could rename that definition “xxxx-cut” ?

Now you edit that component-instance and work inside it.

As @Box has clearly show in the last post, you now need to draw the rectangle, select and intersect, then erase the unwanted parts…
Exit the edit and now you should have a version of that component with its corner cut off…

I almost got it to work by exploding the siding group and passing a plane (made into a group) along the cut line. The first section I deleted worked fine, but the remainders seemed to require deleting each segment. I suspect it is in how I am manipulating the selection tool. Here is the file I am using.siding.skb (151.1 KB)

The SKB file is the backup file.
The SKP is the right one - although simply renaming SKB to SKP makes it usable…

That is indeed a component instance - as I surmised…
No need to ‘explode’ anything…

Edit the instance and make the intersection as @Box explained…
To erase the unwanted parts by fence, make sure you drag in the correct direction - right>left…
Also adjust your view point so it’s easy to see/select…

Remember the ‘make_unique’ tip if you want to keep an uncut version…

It’s the same one I used in the gif above, but as I downloaded and opened the actual siding model I was already inside the component for editing. But mentioning that now is just going to confuse things.

Gentlemen, you have been more than diligent in your efforts to coach me through this process. Your examples were outstanding. Yes, I finally got one to work. I am a little uncertain as to exactly what made it work, but now that I have done it once, I expect to be able to duplicate the cut again. I will certainly save your examples so that I can review them several more times.

Thank you again.

Ahh…reading this thread reminds me of all the things I learned by trial and error over the years. I’d like to add my two cents.

I always make my cutting plane into a group. If I don’t, and any edges touch edges of the geometry to be cut, I will have problems due to the sticky behavior of ungrouped SU objects. If the cutting plane is a group, it can’t stick to any other geometry. The other benefit is that once the intersection is done, I can just select and delete the plane, instead of having to make sure I got all its parts, as I see in some of the illustrations.

Another benefit is that in a complex model where I have numerous components or groups comprising an assembly (i.e., a roof eave with fascia, trim, underlayment, shingles, etc.), I can instead of deleting the cutting plane, cut it (i.e., CTRL-X) instead. Then I back out of the group I’m in, go into the next group in the assembly I want to cut, and paste the plane in place, repeating the intersection process, and doing that for all parts of the assembly. (Hint: make a keyboard shortcut for paste in place. I use CTRL-ALT-V).

Finally, wherever possible, I always use intersect with SELECTION instead of with MODEL. It’s too easy to accidentally intersect with hidden geometry that you can’t see, only to find you have hours of cleanup to do later. Intersect with selection assures that you’re only intersecting with things you can see.

Hope that’s useful info!

I can assure you the hardest thing about making my examples is to do them using the most rudimentary methods.
They are to explain the basic, not more advanced methods.
Usually I also have the toolbar in view and select the tools without using any shortcuts.

Thanks again for all help. I appreciate the comment that the plane should be made into a group. I just made the cut again, and with that suggestion, all went well. I did have to use “intersect with model” as when I used “intersect with selection”, it said there were no intersections.

By the way, as you can tell, I am still a novice with sketchup, but can you tell me the effective difference between a component and a group. If it would be better for me to start a new subject regarding this, just let me know.

Thanks again, Merry Christmas

A group is basically an individual whereas a component is one of many.
If you have several copies of a group and you edit one, it only edits the one you edit.
If you have several instances of a component, edit one and they all edit.
A simple example, build a picket fence with components, drill a hole in one and they all get a hole.
Build it with groups and you spend your life drilling.
Components have other properties also, like glueing and cutting etc

Besides the spot-on info from Box, the other great value of components is to reduce your file size. Each “group” in the model adds to the file size. For simplicty’s sake, whatever one particular group would add, 10 copies of that group would add 10 times as much to the file size. When you make something into a component, each additional instance doesn’t add the additional overhead of the all the geometry, just data about its location, orientation, etc.

This is something you will have to learn in time to plan from the outset of a model. There’s no downside to making your first instance of something into a component rather than a group, if there’s any possibility you’ll want more than one of them. If you have already made 10 identical groups and realize you should have made it a component in the first place, there’s no way to make those into 10 identical components without replacing each one individually with your new component (unless of course someone’s made a script for that).

But if you started out by making it a component, you can save it for re-use in another file (see context menu), and once saved, it can be reloaded to replace another component. And if you decide you want 5 out of the 10 to be different from the other 5, you can select those 5, click “make unique”, and you can now modify one of those to affect all 5. The component is your best friend!

Select them, convert them to components (there is a plugin for that) then use the component browser to Replace Selected. You can replace hundreds in one click.