Sometimes, a simple latch just won't do. In a recent project, I had to design a circular lid that would lock from the inside. However, as I didn't want any hardware showing on the outside of the lid, I needed to keep all the moving parts inside. Using this vault-like mechanism has the advantage of being easy to build if you have access to a laser cutter.

Step 1: Materials & Tools

You will only need a few common items to build this lock.

1/4" Birch Plywood
4 small screws
1/4" dowel
Wood glue
You preferred wood finish (I used wipe-on polyurethane)

Even though, this mechanism can be built with traditional tools, it will be way easier if you have access to a laser cutter and a drill.

Step 2: The Lid

The diameter of the lid is up to you. It doesn't even have to be a circle as long as the arms of the lock still protrude when they are in the "locked" position.

A smaller circle is cut in the centre of the lid. This part, when rotated will give motion to the arms of the lock. In my design, this circle is hollow because I needed to accommodate room for a threaded rod.

Step 3: The Arms

The arms of the lock will slide on a 1/4" dowel. The length of the hollow part of the arms dictates how far these will travel outwards of the lid. Make it longer if you need a longer travel.

Step 4: The Axis

4 hole pockets are drilled on the inside of the lid. Dowels are glued in place. 4 caps are laser cut and drilled halfway through. These will keep the arms in place.

Step 5: Arms Assembly

The arms are screwed on the rotating centre. You can now fit the whole assembly on the inside of the lid, making sure that the axis go inside the arms pockets.

Step 6: The Lid Handle

To rotate the centre of your lid, you will need a handle. I decided to cut a circle slightly larger than the rotating part and glue those 2 together. The fact that the handle is larger prevents the central ring from being pushed through the lid.

Step 7: Finishing

In my project, I use the lid to close the opening of my telescope. As the lid does not have any support, I added some small tabs on the side to make it flush with the end of the tube. It also prevents the whole lid from spinning when rotating the centre part.

If you want to protect the wood from stains and humidity, you can apply a few coats of polyurethane varnish or some linseed oil. As birch doesn't stain very well, I decided to go with a clear finish.

Step 8: The Result

This mechanism is very basic and can be improved on many aspects. However, it is a good starting point for more complex movements. It is also a good project if you are new to laser cutting as almost all the parts can be cut from a small piece of plywood.

If you want to build your own, I am providing an SVG file of the whole mechanism. Have fun with it and please let me know if you've successfully built your own!