I've seen a few of these types of combination boxes and thought they would be great for use in role playing games such as Dungeons and Dragons. Players can discover the box in a dungeon and then spend the rest of the adventure gathering clues to help them open it. The problem I found when buying a box like this is that the combination is fixed and once your group have worked out the combination it it unlikely that you will use it in a game again. So I designed a box in which the combination can be changed, making for a new adventure each time it is discovered in a dusty dungeon!
The box is simple in it's construction, relying on three cams with flat edges that can be rotated. When the dial is in the correct position the flat of the cam is parallel to the front of the box, else the cam is caught under a lip built into the front of the box.
The symbols I used are borrowed from a puzzle game called "Fez" and represent the numbers 0 to 4. A devious dungeon master may use Fez style mathematical equations to lead the players to the right combination, or be even more sneaky and give the answer in Quinary (Base 5 numbers). Or you can simply use your own symbols.
I made this box from scraps of beech wood I had left over. I used a CNC router to cut most of the pieces. Additional supplies include some 6 mm pine dowel from the hardware shop, epoxy resin, wood glue, a small length of brass rod (2.5 mm diameter), and lots of sanding paper. You may also use a laser cutter to make this with minimal modification, which I will point out when we get there.
Step 1: Building the Box
Let’s get started by building the box. I started with some scrap pieces of beech wood which I used with the CNC router to cut the sides, front, and back pieces. The parts fit together with a standard fingered box joint; there is also a rabbet that runs along the base of each piece so when the pieces are joined together the base fits snugly in. The front piece has a groove cut into it which creates a lip that catches the cams when they are in an incorrect position. When the cams are in the correct position, the flat edge does not catch on the lip and the lid can be opened. You may wish to use a laser cutter to cut these parts, in which case a lip can be created by cutting a thin rectangle that is glued to the inside of the front piece. However you make your lip, be sure that the distance between the top of the front piece and the top of the lip is the same (or just slightly smaller) as the thickness of the collar used to make the cam assembly.
When using the CNC router I used a 1.5 mm cutting endmill, which means all internal corners have to have a small relief cut inserted, whereas these relief cuts are unnecessary when using the laser cutter. For this reason I have included 2 .svg files, one for use with a CNC router and the other for use with a laser cutter. The svg files can also be used to print paper templates if you wanted to cut the shapes by hand, with a scroll saw for instance. SVG files can be opened with a free program called Inkscape and will print at 1:1 scale, perfect for template use.
Once all the parts are cut I glued the walls and the base together using gorilla brand wood glue and plenty of clams, make sure the box is nice and square.
Step 2: Make the Lid
The lid was made by V-carving the symbols using the CNC router, they were then painted with black acrylic paint. There is little need to be neat about the paint as excess paint is sanded off once it has dried. The other important feature the lid has is the rounded edge on the rear underside. This is what will allow the lid to swing open without catching on the back wall of the box. I simply ran the lid through a router that was fitted with a round over bit.
Step 3: Make the Dials
The dials were also cut using the CNC router but there are many alternative ways to cut three discs of wood. The dials also had a groove cut into each one which can be done with a dremel or router. These grooves were filled with a mixture of epoxy resin and jet black resin pigment, again neatness is not necessary as any excess resin will be removed with sanding once it has cured.
NB: If I were to make this again I would actually use paint instead of resin as adding too much pigment can cause the resin to not set properly, making it a bit of a guessing game to get the proportions correct. Paint is a more reliable method.
Once the dials were sanded, they were flipped over and the centre was located using the method described in this Instructable:
Once the centre was marked a 6 mm hole was drilled half way through the dial. I used some masking tape on the drill bit to make sure I did not drill all the way through. Cut three length of 6 mm dowel (about 2 inches each) and gle them into the dials.
Step 4: The Cam Assembly
The cams are made from two parts, the cam wheel and the collar. Originally I made both parts from plywood as I was running low on beech but I soon found that the plywood was not strong enough to drill in from the side, instead it just crumbled. I managed to find one last piece of beech from which I cut three collars. The collars are then drilled into from the side with a 3mm hole, the entrance to that hole is the widened using a 6mm drill bit to give a stepped hole, as showed in the picture. The mechanism which allows you to change the combination of the box is the screw that is fitted to the collar, it can be tightened to hold the dowel but also loosened to adjust it's position, thus allowing one to change the combination.
I wanted to use some computer nuts and bolts to do this but found the screws I had were too short, but the standoff screws were just the right length so I used those instead. I recommend trying to find the correct length screws rather than using standoffs like I did :)
The nut was inserted into the stepped entrance and held there with epoxy resin. Once this was dry the collar was mounted on top of the cam wheel and glued into position with wood glue.
Step 5: Attach the Lid
The lid was attached to the box by carefully drilling a short hole through the side wall and a little way into the lid. Again, masking tape was used on the drill but to make sure I didn't drill too far. The lid was then taken out of position and a tiny bit of epoxy resin was put into the newly make holes. The lid was the re positioned on the box and two brass pins were inserted through the holes in the side walls. The resin was left to dry before the excess brass was cut away using a hacksaw, and filed down until they were flush with the sides of the box.
Now all that was left was to assemble the parts. Insert the dowel/dial assembly through the top of the lid, then slide on the cam assembly from under the lid. Position the flat of the cam parallel to the front of the box and set the dial to the desired symbol, then tighten the collar screw to secure the cam assembly.
And there you have it! All that remains is to sand and make your box look beautiful... I think I might stain mine a darker colour :)