Sketchup Modeling for 3d Printing

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Google Sketchup (link) is a great program for someone just getting started with 3d modeling, but there are some common mistakes that you'll need to avoid in order to design properly for 3d printing. Here are some tips and tools in order to get you started right.

Contents

Extensions

Slicing programs can only interpret Sketchup models that have simple outer shells, and are marked "Solid Object" on groups. Solid Inspector extension will show you any faulty triangles and vertices that prevent an object from being a simple outer shell. Essential.

You will certainly need a way to export your file in a useful format, which for us is the .stl format. Sketchup doesn't support .stl out of the box, so we need a plugin, which you can get here.

another plugin that is essential is the Cleanup plugin. get that here, along with a bunch of other plugins you might want. You'll need to create a sketchucation.com account to download :-( .


Good tips for better modeling

click once selects face or edge, double click selects all adjacent edges/faces, triple click selects all connected faces/edges (i.e. the whole moddle under your mouse)

you can do a lot with just the mouse in sketchup, but it's always good to have one hand on the keyboard. Shift-clicking is what you'll be doing half of the time anyway, since it often modifies the tool or intent of your action. Ctrl-clicking and Alt-clicking also do a lot of useful things, so always read the tooltips at the bottom of the screen until you know these by heart.

-Shift select is a +/- select, you you can select multiple objects/faces/edges.

-Middle click orbits, shift+middle click pans

-middle double click will move your view to where your mouse is.

-'k' shows back faces

-'spacebar' takes you out of a tool and back to the select tool

-'m' picks the move tool

-etc. most of the tool quick keys are under the left hand.

Bad form, and how to fix it

Reversed Faces

The most common mistake I see on thingiverse models is reversed faces. If you are modeling with paints/textures, you can see the reversed faces by clicking on view>Face Style>Monochrome.

Su back faces.png the reversed faces are blue-grey. This becomes an issue with .stls creation because the surface normal points inward instead of outward, and will make the model non-manifold.

If you spot a reversed face, click on it to select it, then right click and select 'Reverse Faces'. Su reverse.jpg

Result: Su reverse result.png

If there are a bunch, select a good face, right click and select 'Orient Faces'. This will align all faces to the same state as the selected face, usually. sometimes there are faces that don't want to work, so you'll have to select those faces and revers them manually with 'Reverse Faces'.

Internal Faces

In order to make a clean stl, you need to think of your model as if it was an oddly shaped eggshell. There are only two surfaces, the inside and outside. Each face in the sketchup model has an inside and outside, regardless of it's actual position on your model. Therefore, if the stl converter sees a face in the middle of your model, it doesn't know how to reconcile the inside/outside of that face with the faces around it, and you'll get a ton of errors when you try to slice it.

So, before you convert to stl, always remove all internal faces and extra edges from your model. This can be tricky sometimes, but there are a number of ways to speed it up. the 'k' key will make the back edges wireframe, allowing you to see through the model and see every edge. you can do something similar with view>face stype>x-ray. This makes the faces transparent like glass, which might help if the back-edges option is confusing.

Sometimes, you just have to select faces and hide them (right click> hide) and go spelunking inside your model. In fact, it's often easiest to do this, since hidden edges and faces won't be selected with a drag-select.

for example, perhaps you delete a hole in an object, but now there are edges and faces lurking inside your model. you can hide the front and back face and then drag select all the offending edges in one go, instead of select, delete, select, delete, etc.

Groups and components

Groups and components are excellent ways of organizing your components. You can quickly create a group, copy it, an flip it in order to make a symmetrical part. When you do this, however, be aware that the components themselves have their own axes, which can mess up the stl bed position. you should always explode all your groups and components and place them by the origin before generating an stl.

Also be aware that there is usually an internal face you'll need to remove so that the stl will be clean.


There's a lot of info to cover, and then I'll need to format it all in a clean way, so stay tuned. --Buback 16:13, 22 March 2012 (UTC)

External links