Problem with surfaces in contact

textures
surface
face
modeling
z-fighting

#1

Hi everybody.

I was mading some tries dividing the object I try to draw in different components they assemble well.

But I have some problem, I’ll try to give you an example.

I assemble them like this:

This is what happens inside the model, the textures and faces get mixed.

This is the example file if someone needs to try something:

example_file.skp (171.5 KB)

But I’d like to take advantage of this post and ask several questions:

  1. Ways to fix the problem described above?

  2. Is there any big difference between working with groups and components I should know?

This is what I’ve understood so far. I heard both of them avoid sticking. Groups are a good choice if you’re going to use them once or even if you want to copy them and do modifications without affect the original one. I guess components save file size and if you change one of them it affects all of them. But is there also some different behavior related to “glue” / “snap” / and “stick”.

  1. I’d like my posts could help others to find help in certain ocassions (I know I’ve probably asked things in other of my posts that others already asked before, and I also know it appears a panel that says “Your topic is similar to …”), so … I’d like you to to heard recommendions about the topic title, the tags and the category for a post like this.

Thank you so much for reading my questions as always.


#2

What is the real problem? You’ve drawn the cylinder to the exact same dimensions as the hole. This means the side of the cylinder and the side of the hole are in the exact same location in space. In SketchUp that isn’t a problem. In reality the two parts won’t fit together anyway. If you are trying to make the faces not occupy the same space, make the hole larger or the cylinder smaller. The size difference depends upon the kind of fit you need. How are you going to put the two parts together? coat the cylinder with glue and slide it in? Drive it in with a mallet, or put it in with a 10-ton arbor press?

The main difference is that editing an instance of a component results in all other instances getting the same treatment. This is incredibly power and can save you time and effort. There are other differences that come into play in different cases. At least for the kind of models I create, I have never once found a case in which it made more sense to use groups instead of components and I only use components.

In my mind, the “using it once” thing isn’t a strong argument for groups. And there is the option to use Make Unique when you want to break the relationship between instances of a component. This can be leveraged in a number of ways.


#3

That’s the problem, I mean, I’d like to know if you fix that when you’re designing or drawing something. On one hand, I’m not planning to 3D print a model, but what if I would? what would be the result?, on the other hand, if I make the hole bigger of the cylinder smaller, I guess I will see a gap on the design that will make it look ugly.

Thank you.


#4

I you DID 3d print, you would need to leave a gap.

When you see the two surfaces in the same place, something called Z-fighting is happening. This is due to the fact that SketchUp is a surface modeler (as opposed to a solid modeler). WHen you draw two surfaces in the same place, it is not clear which one should be shown at any given time.


#5

Thank you @TheOnlyAaron

  1. What do you do guys do on your models, do you leave a gap or you don’t?

  2. What do you do in this case? I was trying to design a pencil to spend the time and I thought, I’m going to do it more realistic designing each internal component, the wood and the graphite, the z-fighting is not visible, but it is inside of it.

Thank you so much you both


#6

For most of my models I don’t leave gaps. I do a lot of modeling for woodworking plans and leave no gaps between parts. I allow the person working from the plans determine the needed clearances. For things like doors and drawers, there’d clearly need to be a size difference but how much that difference is depends on where, when and from what the project is being built.

I think that’s time not well spent. In reality the graphite of the pencil would be in contact with the wood of the pencil within a few molecules, at least. Even if you made the diameter of the graphite a few molecules’ thickness less than the diameter of the hole in the wood, you’d still see the Z-fighting. On the other hand, you can’t look at a real pencil in the same way as you would look at a section cut of the model, either.

If your pencil model represents a wooden pencil, did you make the wood as two separate parts?


#7

It all depends on what you are using the model for. For 3D printing, I leave a .15mm gap between pieces. For a model that is never coming into the real world, I model the surface (as I would with the pencil - just as @Daver just pointed out).


#8

Ahhh, you mean the wood are two parts? you’re right, I think I haven’t spend so much time using pencils, haha … now I remember I saw some of them broken in the middle.

You already gave me all info I need, thank you so much, guys, thank you so much @TheOnlyAaron, thank you @DaveR


#9

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