Slicing a model

[gd65]

Hi, I’m having trouble with slicing a model. Every time I do it I end up erasing part of the model on the other side of the cut. My procedure is as follows:

1 Make sure the model is a component or group.
2 Put the model in edit mode
3 Insert a slicing plane
4 Intersect slicing plane with model
5 Highlight the portion I want to delete, and delete.

I’ve seen this done in a similar thread here: Cut object in half
I;m just not getting why this is giving me such a hard time.

Any help appreciated. Thanks.

[Box]

If you attach the model someone will be able to show you a how.

[gd65]

Here is a model that was uploaded by another user…I hope he doesn’t mind me using it for the sake of demonstration.

Untitled (1).skp (398.3 KB)

[slbaumgartner]

Like this?

[Cotty]

@gd65 How did you try it with that file if you only use SketchUp 8? Or do you need to update your profile?

[gd65]

Still the same results…everyone makes it look so easy and I’m still struggling.

[gd65]

Sketchup 2018. Profile updated.

[RTCool]

You need to select the object as well as the plane and perform the intersection. With just the plane selected, only it gets cut.

[slbaumgartner]

I didn’t annotate my animation, so it isn’t obvious unless you already understand, but here’s what I did differently than you show:

• I created the cutting rectangle outside the group and moved it into position. This avoids all issues with the cutter interacting with the group’s contents before you are ready. SketchUp allows things outside a group to overlap things inside the group with no collisions, intersecting, etc.
• I erased the cutter, opened the group for edit, and then did Edit->Paste In Place to put it in the exact same location but now within the group’s context.
• I selected all the group contents and did Intersect Faces With…Selection. I could have made a tighter selection, which in some situations will greatly reduce the time for intersect to complete, but in this specific instance there is not such a vast amount of content that it seemed worthwhile.

[gd65]

I followed everything step for step, still not working. Very frustrating.

[slbaumgartner]

Watch my gif again. Some differences I noticed:

• I didn’t create a component from the cutting rectangle. There’s no need to do that and it affects the results unless you explode it before the intersect. Just make a rectangle and use it.
• After the intersection, use a right-to-left selection box, not a left-to-right. The latter selects only entities that are entirely within the box, and is therefore missing ones that project back farther. That produces those spikes sticking out, as those parts are not entirely within the box.

[gd65]

Same results

[TIG]

@slbaumgartner

After the intersection, use a right-to-left selection box, not a left-to-right. The latter selects only entities that are entirely within the box, and is therefore missing ones that project back farther. That produces those spikes sticking out, as those parts are not entirely within the box.

You still select in the left-right direction !
That misses some edges, and also catches facets you want to keep !

[slbaumgartner]

To further clarify, you did the selection for the intersection using right to left, but you did the selection to clean up afterward using left to right, and that causes your issue!

[gd65]

How did I select in a left-right direction? Looking at the screen, I selected from the right hand side of the screen to the left hand side.

[RLGL]

The article may help with the confusion Selecting things

[TIG]

Pleas rewatch your own video.
You made the two selections with ‘fences’ drawn in OPPOSITE directions.
The final selection should be made right-left - just like the first selection - then everything that was fenced will be included [ensure only what you want to select in included in that fence - by using the correct view during it, or by using Ctrl/Shift key-combos to include/exclude missed/incorrectly included items you subsequently select…].

The direction in which you make a selection fence has different results.
One way selects everything within the ‘fence’ [even partially], the other way selects everything that is wholly with the ‘fence’ [ignoring anything only partially within the fence].

Practice on a simple rectangular face to appreciate the difference…

[Forestr]

In your situation, this is the wrong way to select:

Wrong way deletes edges you need to keep the faces:

Right way doesn’t:

[gd65]

Well…I finally got it… It was like everyone was saying to me, I wasn’t selecting properly, and that was causing all the problems…after reading what everyone was trying to tell me, and reading the link from RLGL on selecting, it made a lot more sense.

Thanks to everyone for your help, it was much appreciated.

[DaveR]

As a note, if you select only the geometry that would be involved in the intersection and use Intersect Faces>With Selection, the intersection will complete faster. And if you work on a scaled up copy of it, you can keep the end face of the cut.