So I recently downloaded Sketchup Make 2017 (Pro trial epxired) and there’s something I don’t understand:
Let’s say I have a flat, 2D rectangle. I want to put some cylinders on top of this rectangle and I want the bottom of the rectangle to stay flat. Whenever I try it though, this happens (view of the underside of the rectangle):
I don’t understand! Please help me - I need it to stay flat
Maybe it would help if you look at it from below when you start to push the circles. They are creating holes. If they stayed filled, you wouldn’t be able to push holes through walls for windows or recesses like mortises to receive tenons.
If you want faces skinning over the recesses you’ve created, use the Line tool to trace an edge segment on the circle. Or draw the cylinders before you make the large face.
Why do you want the holes to be skinned over? What is it you’re modeling?
Thanks for your reply @DaveR - unfortunately I’m a bit of a newbie at this so I’m finding your 2nd paragraph a bit confusing. Could you possibly expand on it a bit more? What do you mean by ‘use the Line tool to trace an edge segment on the circle’?
Sorry to be a pain 
The Line tool is the one that looks like a pencil. You use it to draw lines (or edges as they should really be called). Zoom in close to look at the edge of one of the circles You can see it is made up of a number of short line or edge segments. Twenty four of them by default. Trace one of those edge segments with the Line tool and the hole will get skinned over.
Again, I’ll ask, what are you modeling that you need to do this in the first place?
Thanks @DaveR - that’s worked. Is there a way to get rid of the circle outline on the underside too?
I’m just playing around with Sketchup and this is an issue that has appeared in the past. I created this project purely as an example.
No. If you erase the circle, you’ll lose the side of the cylinder because the circle is required.
It’s pretty clear that you haven’t got a good understanding of the geometry in SketchUp. Faces have no thickness. It would be a good idea to go to the Learn page on SketchUp.com and get started by watching the tutorial videos.
Understood. Can I ‘draw over it’ maybe?
What do you mean by draw over it?
@DaveR Maybe draw another rectangle under it in such a way that it hides the circle outline?
Since faces have no thickness, drawing another rectangle on the existing one would not hide the circles. Make the first rectangle 3D before drawing the circles in the first place. Then pull them up. There’ll be no holes on the underside and you won’t see the circles on the bottom.
Great, thanks for your help! 
Unless the other rectangle is offset below, no. SketchUp geometry automatically merges where it touches unless explicitly isolated in a component or group . As @DaveR wrote, you need to study some to get a grasp of SketchUp basic concepts.
You can also achieve this by making your original rectangle into a group, and then drawing your cylinders on top outside of that group. But as @DaveR said, faces have no thickness so you’ll still see the circle on the bottom, but this method will not create a hole in the bottom.
Thanks for your help everyone!
Group the rectangle before drawing the circles if you want to draw cylinders as separate object. Drawing in SketchUp is very much about grouping geometry into individual objects. For a model to be easy to work with pretty much every distinguishable object should be its own group (or component), whether it’s a car, a building, a cylinder or a wall.
Hello @penguin_k,
Another thing to consider…
You can control whether you see the circle by converting it to a component (or a group) and then moving the group or component to a separate layer where the visibility is turned off. Refer to this linked url for a more demonstrative explanation:
The Trouble with Layers
Seems like every answer posted here misses the salient point; If you use the “alt” key (on a Mac, or the equivalent on PC) with the Push-Pull tool, you’ll leave the original surface in place.
Of course, you can’t erase this, in this case, circle, since it is needed for the desired cylinder wall.
Sorry @franquin, this didn’t seem to work for me. When I held down the alt key and dragged with the push/pull tool nothing happened. (Literally nothing, no movement at all)
It’s Ctrl on the PC.
What @franquin misses is that we were trying to go from where the OP left off and asked the question.
Awesome - that worked.
