How to effectively splitting objects?

RayMobula · October 13, 2023, 2:23am

Hello there, (cc @Grant_Abbitt )
A question on cutting / splitting / separating objects. How?

Here is what I did. I wanted to add a broken pillar to my dungeon. I ended up cutting the column in half using the Bisect + Separate (P) operations. Bisect/Knife doesn’t keep the upper and lower part of the column. It is either or.
On the other hand, Separate keeps both halfs, but doesn’t create a face along the cutting plane to create a closed mesh, i.e., the object remains open. I created a face using Menu >>> Face >>> Fill to fix this.

Is there a better way to split two objects, while keeping both parts, and automagically creating planes to create closed objects?

Thank you for any pointers.
Cheers,
Ray

Grant_Abbitt · October 13, 2023, 7:51am

when you use the split option go to the bottom left corner to change the settings. And yes this is the most effective way generally

FedPete · October 13, 2023, 7:57am

The Bisect tool is very handy in this, but it has a certain usage.

There is no simple click here and you solved your problem easily.
Your solution is a valid and good one!

Blender is a very versatile tool, with generic tools and solutions.
There are plug-ins in the market which easy grunt work, like the retopology of mesh data.
Or simple mirroring. But my experience is that those add-ons will increase Blender’s learning difficulty. More buttons and features to understand. Learn to use the tools Blender provides. With that, you will understand the 3D development process better.

NP5 · October 13, 2023, 10:13pm

It is easy.
If you already have the line of edges you want as the break point, select on half, Press Y then G plus axis etc. to move it if you wish to (probably helpful).

It will not fill the cut ends nothing will really especially if you wanted a custom cut. Well you could use grid fill the loop I suppose but only limited cases you would want the computer doing this rather than your own control.

SO, the image below on the left is the starting object.
Next is the area wanted cut off selected to be kept as another item.
Next Y has been pressed, G and X to move it to the side. (cut area face added post move)
Next is a custom knife cut for a jagged break. Then lower section selected.
Lastly Y has been pressed G and X again and it is done.

Top face created, selected and copied (shift D) G+X snapped to the base of the upper half, perfect fit, M by distance, now the upper half has a matching end cap at the break line.

Separate by selection via P to make the parts separate objects.

RayMobula · October 13, 2023, 9:06pm

Thx. This allows to keep either the upper or the lower part, or the cutting plane. To keep them, I have to create a copy of the object.
Biselect options don’t allow to keep both halfs and fill them.

Comparison: Left, Separate (P), the other one is biselect/knife (K), with fill checked.

Well, if this is the way, then it is what is it.

Back to modeling a dinosaur

RayMobula · October 13, 2023, 10:23pm

Thx. Yes, I don’t want to install any add-ons, and for now go with the functionality blender provides out of the box. This helps to understand why and how things work, or not.

Again, thank you for your reply. Appreciated.

FYI - coming from CAD, I have to rethink how I create and manipulate objects. Not bashing blender, it’s breaking out of routines.

RayMobula · October 13, 2023, 10:18pm

Thx. I’ll give this a try.

RayMobula · October 13, 2023, 11:27pm

Here you go

RayMobula · October 13, 2023, 11:33pm

Found this online. This is helpful too.

Select your edge
Go Mesh > Split > Faces By Edges
Done.

source: Cut mesh into two objects along selected edge - Blender Stack Exchange

FedPete · October 14, 2023, 7:34am

I know, you expect to work, like you’ve learned from other experiences. But Blender is a different tool. Less exact, or mathematical, more freedom and flexibility.
As I said earlier, the bisect tool is more suited for other things like animation.
You’re not the only one in this. Others had the same questions.
That’s why I mentioned add-ons, which will give you a more CAD-like feeling, but a higher Blender learning curve.

Have fun.

FedPete · October 14, 2023, 7:35am

Good find, didn’t though of that one, learned something new, THX for sharing.

RayMobula · October 14, 2023, 5:48pm

Exactly. I largely use Rhinoceros CAD, which was recommended to me by an industrial designer two decades ago. Rhino is meant to work for engineers and creatives alike. So, it is possible to have both.

But blender is free. And blender 4 seems to adopt some features common to e.g., Rhino. Win-Win

Rhino CAD gallery

Back to Dinosaur modeling

sources:

system · October 27, 2023, 1:57am

NP5 · October 27, 2023, 2:19am