Making 3D text printable. Problem to make outer shell

[Box]

I’m going to guess that you are working at a very small scale, this can cause problems.
Have a look at using this method.

The Dave Method

The Dave Method is the clever use of components popularized by @DaveR to avoid the tiny face issue. Sketchup fails to form faces when edge segments get down around the 1/1000" mark. However, tiny faces can exist so the workaround has generally been to scale up your geometry, edit it, then scale back down. This works, but can lead to some issues. The Dave Method leverages the power of components to make life easier. The basic concept is, you start with a component set at the size you want, t…