I have a very basic book I made, just two covers, the pages are all attached to the covers, and a basic 3 part armature. I tried weight painting it so the left cover was fully painted on the left bone, the spine is only the rear, and the right was fully painted on the right bone. Went through every face, but it doesn't have the desired effect. Here's some screenshots for reference, I thought I removed all weight from the spine for both of the bones, but it still has a very weird effect. I'm very new to rigging, so I'm sure I'm doing something wrong but I don't know how to fix it haha. Thanks in advance
For this kind of non-organic object, don't parent With Automatic Weight, parent With Empty Groups, it will avoid some bones to influence some vertices they are not supposed to influence. With Empty Groups creates as many vertex groups as bones you have, with the same names, but there are no vertices affected to these groups for the moment.
Once parented, select the vertices you want to assign to a bone, go in the Properties panel > Object Data > Vertex Groups, choose the group the vertices are supposed to be part of (the group that has the name of the bone that is supposed to control that group), and click the Assign button.
You can affect vertices to different bones, and decrease the influence of the group on some vertices with the Weight value under the Assign button. It may be necessary to make the object more flexible.