Hello everyone!
I modeled a car in blender and created the whole main volume in one mesh. Now, if I want to split the mesh up it always changes the shape of the mesh as well (probably because of the subdivision modifier). Is there a way to split the mesh (seperate for example the windshield from the body to use different materials in rendering) without changing the shape of the mesh? Thank you!
Welcome to BA 
If you want edges to stay sharp with subdivision, you can use edge creases. Separate the windshield, for example, and grab the edges around it. Press W and choose Edge Crease, type 1, and press Enter. Do the same thing on the car model, on the edges where the windshield was.
If I may ask, why are you breaking up your model into individual parts?
if you just want to apply different material to your mesh, you donât have to separate your mesh. You can simply select your faces in edit mode which you want to give another material, select that material and hit âassignâ, like so:
Thank you for your replies so far! The problem is that the shape of the car is quite advanced and the window split is inbetween faces. So even if I can assign different materials to different faces I have to seperate them first. I attached an Image where I painted where the seperation has to be. Unfortunately, If I knife the shape into the mesh, the mesh shape changesâŚ
I think you have no choice but to apply the subdivision modifierâŚ
Though @Blender_Fun1âs method may work in some cases, itâs rather improper, and can lead to some messy results, especially if the topology doesnât match the flow of materials. In a finished asset, each island should be assigned materials, not each face.
You can use a âsplit booleanâ to achieve this effect procedurally. Here is an example of how it works:
The built in bool tool addon can do this process in one click.
Keep in mind that while booleans will work most of the time, sometimes the topology just says no. In this case, either change your topology by moving some verts around, or use a different method, such as @josephâs creases. Good luck.
I doubt this will work and guess you have to apply subdiv as mentioned,
but you can try subdiv with âkeep cornersâ. It works best on open surfaces, for closed maybe use shrinkwrap too.
An âold schoolâ technique been around since (2.7x legacy) if I recall correctly via implementing the shrinkwrap modifier and also guys like Chris Plush have continued improving itâs overall workflow.
Thanks so much guys for your input, great community first of all! I tried all your methods @Charles_Weaver @rigoletto @ sacboi (cant mention more than two people apparently).
Applying the subdiv modifier gave the most âcorrectâ result but for my usecase its not useful because I cant try and correct the outlines of the windows afterwards and also am limited changing the shape of the other parts of the vehicle afterwards.
Actually the boolean modifier makes the most sense to me from a design perspective because I can always change the shape and outlines of the cutout later. The downside is that apparently its very hard on the computer and seems to slow down the workflow but I can live with that. Also Iâm getting artifacts on the boolean cutlines (as shown in the screenshot). Do you have an idea how to smoothen this?
Interesting⌠can you show me the wireframe please? Sometimes booleans have some issues depending on topology.
Also, I would attempt changing the solver to fast. Though itâs more accurate, you sometimes get artifacts with the exact solver.
@Charles_Weaver I already changed the solver to fast because otherwise its even slower 
On the side Window it works really well but on the Windshield/Top not so muchâŚ
Just wondering if youâd resolved the issue?
Yes and no - I increased the levels of the subdivision modifier to about 5 before applying it and using the shrinkwrap to cut. It decreased the problem but it isnt perfect - I solved the rest with photoshop because I only need stills for now. But I still would be very interested in a proper solution!
