Really Basic Basics

Open new canvas. Draw rectangle. Extrude rectangle up into a rectangular solid. Double-tap to select the solid. Move the solid. The original rectangle, the footprint of the moved solid, remains in place as a separate entity. Why? How to prevent this?

Hello, this is direct modeling. After finishing the tools, there is no connection between the sketch and the solid body. If you need to modify the extruded body, just select the particular elements of it and apply any tool to them.

Please have a look at this article if you have some time, it is a detailed description of the parametric and direct modeling approaches:

Thanks for replying; however, I was looking for much simpler, frankly operational answer.

Let me try asking again: why does an extruded rectangular solid, when moved, leave behind its original drawn rectangle as a separate entity? Why is that original rectangle still there after it has been extruded from a plane figure to a solid?

My guess is I’m doing something very simple very wrong. Wha…?

You are not doing anything wrong. The sketches and solids are two separate entities. Once the solid is created, you can work on it separately, or continue to develop the sketch further. You can delete the sketch if you want, or hide it using the folders view. Keeping the sketch is handy when you need or want to go back to the original concept.


I guess I get it, I guess…

If a 2D “sketch” is made (and I am assuming it is a closed form, e.g. a rectangle), I get that that form is an entity unto itself.

If the form is altered—say, extruded to become a 3D entity—I don’t understand why that developed sketch still leaves behind the 2D sketch as a sort of a ghost of its past. Doesn’t the 2D rectangle become an integral part of the solid, as the solid’s bottom or top face? Why is that residue of its origin still in existence?

Thanks for telling me I’m doing nothing wrong. That’s rarely true, but it’s nice to hear. At the end of the day, though, in none of the online tutorials do I see the thing happening that I’m seeing in my drawing. 2D becomes 3D and gets moved hither and thither with nothing left behind.

I’m beginning to wonder if this is not a matter of terminology.

Eventually I will grok it.


Well, I re-use those sketches all the time. If I don’t need them, I’ll either delete or hide them. But I have found it wiser to hide them.

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I think that maybe looking at this with just a cube is too simplistic. I use quite complicated sketches of, say, a section through a building which has many different elements all needing to be extruded separately, in combination, or a bit of both. If every time I extruded a part of the sketch and that part disappeared along with the 3D extrusion, I’d have to redraw that part of the sketch.

Also, as mentioned, the sketch is something that can be developed. Think of the sketch as a die which can be modified after each extrusion rather than having to make a whole new die each time you what to make a small change.

My models can get quite cluttered with loads of small, simple one-off sketches so I just do a bit of a purge now and then, but I tend to just hide the main sketches for future reference or updates. I would prefer to have to purge/hide than to have to constantly redraw sketches.

Hope that helps.

Yes, it does. Thanks for your explanation & its rationale.


Another example is if you want to extrude something but offset the extrusion. With the sketch remaining in place, you can first extrude to the “top” end of the desired extrusion and then do a negative extrude to offset the “bottom” end. I do this often when designing various features of a model because it allows me to lay out the entire model on one sketch. There are exceptions where this doesn’t work, of course.