You are probably already familiar with the classic "Secret Book Compartment" project. On Instructables alone, you can find over 20 different variations of this project. The basic concept is simple. You hollow out a large book and you use the cutout space to hide stuff. Unfortunately, most versions of this project have one major problem. You can only hide objects that are smaller than your book. However it is possible to hide larger objects by combining multiple books into one large multi-book container.
Step 1: Select a Set of Books
There is no specific kind of book that you need to use for this project. Just about any book can work. But here are some guidelines that may help.
1. The height and depth of the books are the important dimensions of the book. The size of the cover is what limits storage space. Since you are using multiple books, the thickness of each one doesn't matter.
2. The books do not need to be the same size, but it is convenient if they are. Sets of reference books like encyclopedias work well because they are all the same and it is a reasonable excuse to have a bunch of large books all in one spot on the book shelf.
3. Hardback books hold their shape better than paperbacks do after being cut up.
4. The secret compartment only remains a secret as long as no one tries to read any of the books. So it helps if the book are relatively uninteresting while still looking like something that you would have on your shelf.
5. A good source for cheap books is community book sales. Many public libraries will have a large book sale
once a year. On the last day of these sales the remaining books are typically sold at a huge discount. You can often get a whole bag full of books for just a few dollars.
6. Get more books than you think that you will need. You must have one unaltered book on each side of your compartment, but I recommend having two or three so that if someone is messing with books on the shelf and a few fall over, it doesn't reveal your hidden compartment.
Step 2: Measure and Mark the Dimensions of Your Cutout.
Place the object that you want to hide onto one of the books. Then mark its outline of the object with either pencil or tape.
Step 3: Cut Each Book
There are a number of tools that you could use for cutting the books. Since this project requires you to cut through entire books, including hard covers, you will probably want to use a power saw. I personally prefer to use a scroll saw for this kind of job, but other power saws can also work. Whichever tool you use, I recommend using a fine toothed saw blade. The finer the teeth, the less it will tear up the cover and the pages.
Step 4: Glue the Books (Optional)
Gluing the cut books together will help to make them more stable and easier to move around. However, if you aren't careful, books that are glued together can look unnatural in how they sit on the shelf. So if you glue them, I recommend pressing them sitting in the position that they will be on the shelf. If you don't have a large clamp, you can press them by placing them on the self and using other objects to apply pressure to the stack of books. One example is to place them on the shelf, add more books to the shelf until it is almost full, then insert a rolled up t-shirt or towel to apply pressure to the books.
Step 5: Finished Multi-Book Container
Now just place the books on the shelf and you are ready to hide your secret spy stuff.
Step 6: Other Book Container Instructables
Here are other book container instructables (in order of views). They demonstrate a variety of materials and techniques that can be used when making this kind of project.