Splitting a model in half

I’ve got a box created but I need to split it in half lengthwise. I inserted a rectangular face at the split point, selected all, then chose Intersect Faces With Selection. I can then select the left half and group it. Then I’m able to move it out to the side. Everything seems sealed up on that half. I can’t figure out how to do the same with the other side. I don’t know enough to explain it correctly but selecting FROM left to right seems to give me results different than selecting right to left.
I feel I’m close but no cigar.

You are right that L/R, R/L selections give different “selections”. Try re-orienting your model 180º so you can L/R select the other half.

You want two mirror-image opposite halves?

Perform the Intersect as you have been doing and select and delete half the box (using a right-to-left selection window) along with what’s left of the intersecting rectangle. Now you should have one perfect half. Now slide a copy (Ctrl-Move) of the box-half next to its parent (noting the axis you slide along), and with the copy still selected, right-click > Flip along [use the axis color you just noted].


I like Gully_Foyle’s answer better than mine.
Here’s a help.sketchup tut on selection direction.

I should observe at this point that my name used to be Solomon some time ago. Yes, that Solomon. So splitting the box in two seemed like a no brainer to me.


I forgot to mention the box is slotted at one end so it’s not a mirror image scenario. I’m still wrestling with the selection thing. What I did was make a copy of the model and rotated it 180. SO I go through my original process with the 1st copy and get my half model (with the slot). That’s fine. I go to the copy thats 180 and try to do the SAME process but the selection does not work the same. If I try to left->right select the left half (of the 180 copy) it selects the whole box -except for the very right end of the box. I’m thinking it must be something I’ve neglected to do ON the model maybe thats causing it to behave this way.
The image doesnt show it but the copy on the left was all selected except for the “right” end of the box.
Domino Box - fixed.skp (102.5 KB)

You need to understand how the selection fence works.
Right to Left (a dotted line box) selects everything it touches.
Left to right (a solid line box) selects everything that is entirely within the box.
Ctrl with the selection adds things to the selection and shift either adds or removes them.

So here you see I right to left select the parts I want to intersect, intersect, then right to left select the right side, the using shift deselect the guides and make it a group.
Then right to left select the left side, deselect the guides and make that a group.

There are many different ways to do things, this is just one example.

So make a copy of the original box and delete the north half of one and the south half of the other.


!!!Thank you!!!

Done! Got em. Gotta seal them up but I can do that. I also wasnt unselecting my guides but would that matter really?

The animation was so helpful.

Thanks again.

Yeah no matter how you do them at least one needs a face or two added to seal them up.
The guides don’t really matter but in some cases you wouldn’t want them as part of the group in others you would.
Just for reference here is the same thing done the other way, with a solid selection box. Selecting all within it. Notice it doesn’t select the guides, or the cutting plane.
You can see how it adds the geometry from the slicing plane to the group. In this case the second group is now glued to that plane, so won’t move along the red axis unless unglued. (right click/Unglue)