Simplifying the Intersecting with Faces function


#1

I don’t know why I’m having so much trouble getting the order of operations right but I want to take object 1 (which is larger), insert object 2 half-way into object 1, then intersect faces with model. Then I want to delete all of object 2 so that I’m left with the negative space.

No matter what order of grouping, ungrouping, exploding, not exploding, I do not get the smaller object 2 to leave negative space. I only get the outline of the shape on the surface.

When I search for how to intersect with faces, it doesn’t mention anything about grouping or ungrouping, and yet with both exploded I have the same problem.

Does the smaller object have to be inserted all the way through the larger object for intersect with faces to work?

Thanks for any advice.
Rick


#2

When you intersect faces you are creating new edges where two faces intersect. You then need to remove the relevant faces to create the ‘void’.
SU is a surface modeler, not a solid modeler. You need to understand every surface is made of a number of edges and a face and behind it is nothing.
A cube is 6 faces with nothing inside it. If you intersect another smaller cube with it it will create edges on the intersecting faces but it’s up to you to remove the correct excess and leave the right bits.


#3

This is your problem. You must delete only the parts of object 2 that protrude outside object 1, and leave the parts that border the negative space inside object 1. Intersect with creates edges where faces intersect, but it does not create anything “inside” object 1 where there is nothing to intersect with.


#4

Thank you both for the explanations. I would have thought if I select the entire smaller model, as long as I did “intersect with model”, then there should be an entire negative space and sketchup would simply make the new faces inside the “hole”.

Even if select just the face of this fish, and not the whole object, when I delete things, I still end up with only an outline on the surface. (I turn on x-ray view and see that no part of the models exists underneath, and if I delete the new outline surface, sure enough I have nothing there.

I made a video to illustrate. Guess I’m missing something really simple here? I will try again to just delete the surface parts of the fish after intersecting with model. I think I have only tried that once and I may have just messed up the order.

[URL=http://tinypic.com/r/14mx6ag/8]View My Video[/URL]


#5

Problem Sovled!!!

You both found my problem. I simply had to make sure I was deleting the sufaces I don’t need individually in order for it to work.

Thanks guys.

Is there no option to delete an object that is inside another and have sketchup only repair the inner faces rather that just repair the original surface faces?

Thanks again.


#6

After creating the intersection, you need to leave behind some of the smaller shape to form the hole.

Here’s a simpler example showing the mitering of a piece of molding. After the intersection has been made the outside edges of the angled cutting plane get deleted but part of the cutting plane remains to create the face of the miter.
Cutting Plane

Remember SketchUp is not a solid modeling tool.

Edit: Maybe the above will make it clear why you need to keep part of your “smaller object”.

Keep in mind that all the faces need to be in the same context.


#7

Yes, thanks. I do need to learn better how sketchup works. I can see how my incorrect assumption was my main issue.

I will continue learning more about it. The last few days I studied many videos but obviously need to learn more about how it works.


#8

Solid tools are made for that. But they only automate what intersect does.


#9

OK, thank you a bunch.


#10

That’s what the Pro version’s subtract solid tool does, but not what Intersect Faces With does. IFW is quite literal: it creates a new Edge wherever a Face intersects another Face within the chosen context. If the part of the smaller model inside the larger one does not have any Faces intersecting other Faces, the tool will create nothing there, though it will leave the original smaller object in place. Cleaning up and preserving bits you want to keep are left as manual follow-ups.


#11

Ahhhhh, I didn’t realize there was a “subtract solid tool” way of doing this as opposed to intersect faces.

That is really helpful to know! I will try it that way too and see how I like it.

Thanks for the heads up on this, and Box mentioned solid tools as well. I’m googling them up now.


#12

The Intersect command creates edges of intersection (lines) within the context in which it’s invoked.
Like @Box says, once the faces are cut by the new edges, simply erase what you don’t want.