Secret Desk Compartment

I had been browsing Instructables in the past for ways to make secret compartments, but I wanted to make my own secret compartment that was unique. So, as my first Instructable I've decided to share my the design of my secret compartment.

First of all, as part of my design, I decided that the compartment should be strictly mechanical. I sometimes forget to charge things, so any electronically triggered mechanisms were a no go, and the last thing I wanted was to have to damage my compartment to get it open. I did not have enough room for false bottoms in the drawers as they are very shallow, and I felt that a false back would be too obvious. So, I decided to try to create a panel that would float in one of the empty spaces below my desk.

Previously, I had been using an Altoids container which was magnetically attached to the bottom surface, but I wanted something that could provide more room.

The materials needed for the project will vary slightly depending on the desk or furniture. I want to create this Instructable as a guide for your own furniture, based on the steps I took to make it work in my furniture.

I used the following:

• plywood board (the thinner the better, used only for appearance)
• thin metal rods
• a sprocket and compatible chain
• small nuts and machine bolts
• small wood screws
• Plexiglas
• some scrap wood
• epoxy

Equipment:

• Table Saw or Circular Saw
• Drill
• Sandpaper
• Dremel
• Lots of Clamps
• Ruler/Tape Measure
• Markers/Pencils
• Scrap Paper

As with any project, I went through several iterations and ran into many problems when designing the compartment. I did consider using magnets to lock the compartment panel into place, but I was concerned that I would not be able to manipulate the magnets easily as I would have to come at them at a bad angle. I also considered having the panel lock in place by pushing it into some kind of door catch, but I decided this would be to complicated as I would need to find a way to keep the panel parallel to the ground and unclip multiple catches. I even considered the catch idea in combination with an arduino knock response to release the catches, but I wanted the safe to be accessible even if the power was out. Also, the vertical space in my compartment was very limited, so if I included an Arduino or catches, I would have not room to store my stuff.

I ultimately decided a mechanical mechanism in the form of a sprocket with 4 rods which would simultaneously translate upon sprocket rotation as I believed this would be more reliable for long term usage. Additionally, my design allowed for the panel to be very slim (~3/4" in height including the plywood, sprocket, and Plexiglas).

For the design I ultimately decided on, I was able to drill holes into the furniture to support the mechanism weight. I would recommend a more case by case basis for different furniture limitations.

To determine the rod lengths needed, I created this picture guide for myself (above). I drew a model of the panel layout to scale. I only sized one half, since the other side will just be a mirror of the other side. Also, I only drew the panel such that the corners are where the rods will enter the desk (5/8" from lengthwise sides).
So, the first thing I did was line up the sprocket in the center of the board. Next, I drew a concentric circle on the sprocket (use a compass) which would allow me to drill a 3/8 inch hole for the rod connections. I was trying to achieve a 0.5" translation on all four rods when opening or closing. In order to do this I found two points on the concentric circle on the sprocket which are collinear with the corner the rod would be translating into. The two points (I have marked them green-open and red-closed) should be the translatable distance apart (0.5"). After I found the correct line, I found the rail length. The length was the distance between the green and blue points. By drawing the image to scale, I could simply scale up to find the correct rail length.

When sizing the fake panel, I had to make sure I got the measurements right. The fake panel is the most important part because this is what everyone will see. I would recommend cutting the panel to be slightly larger that the space it is meant to occupy. That way it can always be sanded down to fit more snugly. The plywood used should be thin to maximize compartment space. The panel was designed such that the plywood would not have to support weight while locked in place.

My slot space measure as 23 3/4" by 5 5/8", so I cut the plywood so that I could take off an eighth of an inch on each side. Additionally, the spot I was using had two areas where the furniture's decorative molding jutted out. I carefully measured these and cut the plywood accordingly with a jigsaw.

The top my panel was a piece of Plexiglas. I chose Plexiglas because it would be easier to line up the top and bottom, also I thought it would look cooler if you could see inside. To cut Plexiglas, mark the area you need to cut, then score it with a blade. Depending on how thick your Plexiglas is you may need to score it more. After it is scored, just bend it and it should break along the score.

From the design, I redrew the concentric circle from step two onto the sprocket. The green point from each rod measurement needed to be drilled into the sprocket. Be sure to lubricate the drill site with oil so the titanium bit doesn't get damaged. Also make sure the sprocket is clamped down. I would recommend using an electric plug in drill if you have one as you need a lot of torque.

Cutting the rods to the correct length was the next step. The rod lengths, determined in step two should be cut a little longer than needed an grinded down when fine tuning the mechanism. I clamped the aluminum rods and cut them with a hacksaw. I cut two rods with a length of 12.25" and two rods with a length of 11.50" .

Next, I attached the rods to the sprocket via bolts which the rods were glued to. I was originally going to cut a ravine in the top of the bolts I got to keep the profile as low as possible, but the tools I was using were cutting way too slowly. So I instead hammered the aluminum rods flat and used epoxy (JB Weld) to attach the flattened ends to the heads of the bolts. I then inserted the bolts into the holes I drilled and kept them loose so they could spin freely.

Finally, I cut off a piece of threaded rod which would fit into the center of the sprocket. This would keep the mechanism together and centered on the panel.

I would recommend using some scarp wood or something similar as guides to make sure the rods only translate linearly. This will also help to ensure that the rods come out at the corners of the working space. I used wood glue to attach these guides to the plywood. Additionally, I used wood screws to attach the guides to the Plexiglas to make the panel more solid.

This part was a little tricky. The lever that I used to rotate the sprocket is made up of components from an Erector set. However the basic principle is this part of the mechanism needs to be able to pull the chain on the same side as where the rod is pushing on the lever. I used epoxy to keep the sprocket in the center and the lever in place.

During this step I was making sure that all of the components were not running into each other and fine tuning the rod lengths.

Using excess rod pieces I pushed on the lever to close and open the mechanism. The first and second image shows the mechanism opened and the third and fourth image shows the mechanism closed.

Now that the mechanism is fully assembled, I tested to make sure there were no major collisions or other errors. I did this before putting the panel in the slot in my desk because I cannot see the mechanism when it is in my desk, so I would not be able to see any major errors.

When drilling the holes for the rails, make sure the holes are larger than the rails. This will make it easier for them to slip in.

Very Important!

Making your furniture compatible with your compartment should be one of the final steps!

Make sure to measure twice and cut once. Make sure your area is well lit and don't be afraid to mark up your furniture (pencil or something that can be erased).

For this part, I held the panel into place while turning the mechanism to lock the panel in place. Mine is pretty seamless. It appears I chose the correct stain color. I guess the next step would be to fill in the slot on the other side of the desk. :)

*I added a video demonstration to show the mechanism in action, for anyone who wants a little more detail.