Intersect Faces: more clarity sought

I’ve learned a good deal of the ins & outs of Intersect Faces but as a relatively new user there are still a few things that puzzle me. All of the explanations and tutorials I’ve found online address the parts of the feature that I already understand and they gloss over or don’t address the remaining issues I don’t fully understand. Here are a few questions.

  1. Most of the tutorials I’ve seen on Intersect Faces start out like this: Person makes a box and a sphere then crams the sphere into the box so they overlap. Then they go on and explain the feature as you would expect. But here’s the question/issue: The geometry used is not turned into groups first. So, would this even be done in a real world work flow? With sticky geometry how on earth would one begin to position the geometry accurately (in this case the box and sphere) if as soon as they touched they’d be sticky? So, am I taking this example too literally? In other words, are these types of tutorials merely showing the basics of the Intersect Faces feature using a workflow that would not be of much use in reality? I’m assuming that expediency is the primary reason for showing the feature this way but I may be overlooking something.

  2. Related to what I mentioned about Groups and Components above: If the desired or pretty much required workflow would be to avoid ‘stickiness’ when geometry is overlapped, wouldn’t the Solid Tools features (Intersect, Union, Subtract, etc.) be that way to go? That is IF all the geometry in question is properly closed and can actually be a solid if grouped or turned into a component. Just trying to get a grasp at how Intersect Faces and Solid Tools are used and when. So, first assumption is that overlapped geometry should always be in Groups or Components. Then from that would it be reasonable to say that in most cases, if the geometry is closed (and can be turned into solids by grouping or created a component, use the Solid Tools. If not closed, and thus not solids, then use Intersect Faces? Does this sound at all reasonable? :slight_smile:

Note: With regards to Groups and Components and Intersect Faces I didn’t mention the With Context option because it wasn’t directly relevant to my workflow related questions. So, if anyone was inclined to offer a ‘brain dump’ on it, because you may think I’m not familiar with it, I already am. Not trying to be persnickety here…I just know that you guys are extremely generous with your help and time. A great thing! However, I’m trying to focus the discussion and no need to elaborate on something I’m pretty much clear on. However, if you think that there are some aspects of that option I’m overlooking with regards to the Solid Tools vs Intersect Faces issue, then yes, please elaborate.

Thanks for any info…jonR

you can only use ‘solid tools’ with SU Pro and ‘solids’…

if using SU Make or Web versions you only get ‘outer shell’…

there’s a handy trick to master, particularly when creating convex geometry without solids…

if you click and release to ‘grab’ a preselected object to move, it will not ‘stick’ until your second click…

it was more common practice before ‘solid tools’ existed but is still used by many…


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Thanks for the clarification about version of Sketchup; I was assuming SU Pro and I should have explicitly stated that. But I’m pretty sure I implied that Solid Tools only works on solids; pretty sure that wasn’t on the table as a question.

Thanks for that tip. That’s something very basic and good to know that I quite frankly have been overlooking about the move tool. But even so, it seems a bit limited for exact placement before the second click. Not sure if it’s a matter of practice or just inherently limited.

you can intersect faces within groups to the outside context or between faces in the same context. The results are different. If you have faces in the same context that will give you more complete shapes… a simple way of saying it–try it out. Yes you can move objects together, but once you complete the move it may be hard to move again without geometry sticking.

Your option is to a create a group, position it, and then explode to get the faces back in the same context. Since most of my work in already in groups or components. I might create new faces outside the group and position then then paste -in place into the group.

Right; I’m already familiar with in / out of context works with intersect faces. Your suggestion of ‘try it out’ was indeed something I already did…before I posted my question(s). My questions as I stated, were not about the mechanics of how to use the feature. I’m pretty sure I stated I was already familiar with the feature. If you re-read my post, particularly #2, you’ll see it was a workflow question, not a request to explain how a feature or features work. The question was something that I was wondering about that came up after being familiar with the intersect faces feature. I was just wondering that if someone was using SU Pro, and thus had access to the Solids feature, why would you want to even use Intersect Faces? Of course the geometry you were working with had to have the ability to be turned into solids (no openings). So, if that was the case, and the geometry could be turned into solids by group or component, why not use the Solid Tools to intersect, subtract or union? That was my question. It was merely a question to people in this group who have used SU Pro longer than I have and as I said just earlier, it was primarily a question about workflow and choice of tools.

I probably use Intersect Faces more than any of the solid tools, but both have their place. When I want to create a shape that I can’t just draw directly, I’ll use Intersect Faces. For me, modeling all kinds of furniture, the best example is a cabriole leg. I’ll extrude one leg profile, copy and rotate it, then explode the copy and use Paste in Place to put it in the context of the original. Then I use Intersect Faces to join the shapes and erase all the waste. That’s my work flow.
If I’m modeling something like a Windsor chair, with turned rungs connected to turned legs, I’ll use the Solid tools Trim to create the holes in the legs for the rungs. If I’m feeling frisky, I may use Eneroth’s version of Trim. Solid Tools has one drawback: It changes a solid component to a solid group, which forces me to change it back to a component. Messes up my work flow.

(at the risk of being snapped at like above, to @john_drivenupthewall and @pbacot)

Manipulating ungrouped geometry into position, for whatever reason, can be a big risk, like you stated. You (one) should at least have one chunk of geometry grouped before doing so. (also mentioned above by others)
So yes, to me it seems that these tutorials you mentioned just show the basic concept(s) of ‘Intersect Faces with…’ and not the best work flow.

Why use ‘Intersect Faces with…’ if there are the ‘Solid’ tools?

  • maybe you only want the intersections, the wire frame of geometry.
  • maybe you want these edges to get created in one context or another.
  • maybe (and this is certain) ‘Solid’ tools do not work on solids that are in different contexts, and you still need them (their faces) to somehow intersect.
  • maybe you wish to intersect selections that not have just solids in them.
  • maybe you don’t have all the ‘Solid’ tools at your disposal.
  • maybe something else that I’m not aware of right now.

So it more or less depends on your work flow and what you have gotten used to.
If you have mastered the concept of ‘Intersect Faces with…’ (all its options), then I think you are good.


David, thanks for your discussion on the pros/cons from a workflow perspective; very helpful. One of your points touched on something that I overlooked in my question: creating profiles. That is obviously something that Intersect Faces would be used for. Also, when I was playing around with Intersect faces with different types of geometry grouped and ungrouped I found Paste in Place very useful for transferring profiles from one context to another. (something you mentioned). Your heads up about solids changing solid component --> solid group is an appreciated heads up.

Dan, thanks for this; very helpful; exactly type of info I was looking for.
Btw, I didn’t mean to ‘snap’ at those other guys; apologies if it was taken as such. I try to think about my questions and focus them before I post… I don’t expect people to teach me the steps of a particular feature…that’s on me and I can do that on my own before I come here and I did just that before this question. So, if I ask a question or questions its usually about top level workflow issues, not ‘in the trenches’ questions about making a feature work. I’m pretty sure my questions were crafted in a way where I wasn’t asking for help on how to specifically use a feature. And a lot of that is because I don’t want to take up people’s time on that stuff. So, in my responses, I was merely trying to shift away from.having the discussion devolve into a feature tutorial direction.
Thanks again for your feedback! -jonR


Always glad to help.