Introduction: Wooden Keep Sake Box With 4 Digit Magnetic Combination
I've always had a fascination with puzzle boxes, wooden locks and magnets, so when the magnet contest was announced I thought I'd incorporate all three into one. I wanted to come up with a lock with a changeable combination and decided to use four tumblers with each one containing nine possible magnet locations, that gives a total of 6561 possible combinations to unlock the lid!
The basic premise of the lock box goes like this; moving the apparently fixed handles on the ends forward causes 6 rare earth magnets on wooden pins to pop out, then using those magnets on the lid to slide the tumblers inside of the top ( also containing magnets ) to specific number locations. Once the correct combination is met, the main locking bolt is free to move ( by using another magnet ) which unlocks the box and frees the lid to pop open (using the touch-latch pin).
I used millimeters for most of my measurements because when working on something this small it is far easier to mark out,( and being a Canadian were suppose to be on the metric system eh ;-) but I included the imperial measurements as well.
Take caution when working with rare earth magnets!! They are very strong and can snap together quite violently (ouch) !
Please be sure to keep them away from young children, they are not a toy and are very dangerous if swallowed!!
32- 5 mm x 5 mm rare earth magnets ( Amazon )
6 - 8 mm x 3 mm rare earth magnets ( Amazon )
five minute epoxy, masking tape, carpenters glue, wipe on finish
solid - maple, black walnut and beech
# 6 x 1'' pan head screws , # 6 x 3/4'' pan head screws, touch latch pin, 2 -5 mm shelf pins
table saw ,planer, miter saw, sander, drill press, basic hand tools, dado blade, 5 mm and 10 mm brad point drill bits
patience... lots of patience...
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Step 1: Top Construction Part 1
The first thing to make is the center section, which is made up by alternating 8 strips of walnut ( 2 mm wide x 14 mm thick ) and 9 strips of maple ( 8 mm wide x 14 mm thick ) all around 76 mm long ( 3'').
Tape the pieces together on one side then open up on the other side and apply glue, lay flat, clamp and remove excess glue, let dry.
Step 2: Top Construction Part 2
Cut a piece of walnut approximately 500 mm (20'') x 200 mm ( 8'' ) wide and plane down to 14 mm thick, rip into 3 pieces with the middle piece being 76 mm (3'') wide. I used one board instead of three separate pieces to maintain the grain pattern on the top.
Take the center piece and cut it in half length wise. Glue and clamp one piece to both ends of the alternating maple and walnut center section. Clamp it in between two scrap pieces to keep it straight or down to a flat surface and let dry.
After the piece is dry carefully rip into 12 mm ( 1/2'' ) wide strips using a fine tooth sharp blade in your table saw.
Step 3: Top Construction Part 3
Cut and mill 2 pieces of walnut and 5 pieces of maple 5 mm thick x 14 mm high and 500 mm ( 20'' long ). Cut the strips as in the first photo, alternating the maple and the walnut.
Line up the pieces including the two outside pieces and tape one side, flip over and apply glue in between each piece, lay flat, clamp and let dry. Note - remove excess glue with a scraper before it fully sets, or wipe with a damp rag.
After the piece is dry, sand both sides flat.
Step 4: Tumblers and Top Dados
Set up a 10 mm wide dado blade in your table saw and then cut four dado's 10 mm high down the four strips in your layup. Sand inside the dado with a small block and fine sandpaper.
Mill some strips 9.5 mm x 9.5 mm ( I used solid beech wood ) and cut to 220 mm long. You need four for the tumblers, one for the locking pin and a couple of extra for the bolt latch pieces. So 7 in total.
Line up the tumbler pieces and tape them together, mark 9 lines, 10 mm apart. Set up your drill press and drill 5 mm diameter holes 6 mm deep on all the lines on your tumblers. Lightly sand the tumbler sticks and make sure they all slide easily in the dados of the top.
Step 5: Tumblers and Locking Pin
Center the four tumblers in the top piece with the holes facing down and tape in place. Using the same 10 mm dado set up as before, run a cross cut dado exactly in the center only 3 mm deep ( 1/8'' ) ( this is for the locking pin to slide in ). In the same cross cut dado ( only on one side of the tumblers ) raise the dado back up to 10 mm high and cut up to the tumblers but no further.
Draw on your locking pin where the tumblers are located, then cut a 3 mm x 10 mm wide dado across the locking pin. On one end of the pin glue a 7 mm x 10 mm ( tapered up on one end to match the dado saw cut ) and drill a 5 mm diameter hole 10 mm deep ( for two magnets to be glued in ).
Make three pieces with a 10 mm x 7 mm deep dado in the center 100 mm long ( 4'' ) these are to hold the locking pin in position.
Step 6: Box Construction
The sides are made up of three pieces glued together. The bottom maple piece is 88 mm high x 16 mm thick ( 3 1/2'' x 5/8'' ), the walnut strip in the middle is 16 mm high x 16 mm thick ( 5/8'' x 5/8'' ) and the top maple piece is 38 mm high x 16 mm thick (1 1/2'' x 5/8'' ).
The two sides are roughed out at 500 mm (20'' ) long and the two ends need to be roughed out at 230 mm ( 9'' ) long with an exact 76 mm ( 3'' ) opening left in the walnut space. The two ends were done in one long piece as opposed to two separate pieces so that it would still be able to run thru the planer .
After the glue is dried run the pieces through the planer and bring down to 15 mm ( 9/16'' ) thick. Sand both sides and then miter the ends of all four pieces using a miter saw or a cross cut sled on a table saw .The finished length of the sides is 445 mm ( 17 1/2'' ) long and the ends are 202 mm ( 8'' ) long.
Cut a 6 mm x 6 mm ( 1/4'' x 1/4'' ) rabbet down the inside on all four sides for the bottom panel to sit in. Glue and tape the four sides together and then machine a 6 mm (1/4'' ) thick bottom to fit.
**Do not glue the bottom in until you are sure the lock works correctly !!!!
Step 7: Dowel Pin Holes
To drill the dowel holes I made up a 38 mm ( 1 1/2'' ) template block with three 10 mm holes 22 mm ( 7/8'' ) from the edge and 41 mm ( 1 5/8'' ) apart, done on the drill press to ensure the holes were straight up and down .
Cut two pieces of 15 mm thick solid stock the inside width of the box times the inside height of the box minus the thickness of the top, clamp the template block and the inner piece to the box. Drill the three holes 30 mm ( 1 3/16'' ) into the inner piece. Do both ends and then on the back drill the same hole pattern just deep enough ( 6 mm ( 1/4'' ) deep ) to glue fake walnut plugs into ( so the back to matches the front ).
Step 8: Handle and Interior Slider
Remove the inner pieces and cut a 25 mm ( 1'' ) strip off the ends with the holes, glue the two strips into the front corner of the box using the drill bit to align the holes. In the off cut pieces drill three 5 mm diameter holes 6 mm deep where the dowel pins will line up. A magnet will be glued into these holes to hold the dowels in when the handle is drawn back.
Cut the two slider pieces to 101 mm ( 4 '') long. The handles are two blocks glued together, the outer block is 150 mm ( 6'' ) x 22 mm ( 7/8'' ) x 16 mm ( 5/8'' ) thick, the inner block is 16 mm ( 5/8'' ) thick x box side thickness plus a hair ( to allow clearance for the handle to move ) and 51 mm ( 2 1/4'' ) long, offset the inner block by 19 mm ( 3/4'' ) on the outer block when you glue together.
Move the handle and sliding block all the way forward, clamp and screw together ( always pre drill your screw holes ). The handle should now move the inner block back and forward. Move the handle all the way back and cut the remaining piece of the block to fit. Drill and glue two magnets into the back of the slider piece and the rear block ( match up magnets ). This is to hold the handle in the closed position.
Step 9: Magnetic Pin Construction
The pins are a 10 mm ( 3/8'' ) dowel with a 5 mm hole drilled 11 mm deep in the end using a drill press. Glue two 5 mm x 5 mm magnets and one 8 mm x 3 mm magnet into each of the dowels using epoxy ( photo #2 ). Make sure you have the same polarity on all six pins !!
Sand the dowels so they slide easy in the holes and cut slightly longer, Then sand down flush to box with the pins in the retracted position.
Step 10: Other Bits
To position the back pins on the lid, drill two 5 mm holes through the back into the lid. Glue 5 mm shelf pins into the back of lid and plug the holes in the back of the box half way with the walnut plugs.
I used a spring loaded pin ( used for touch latch doors ) and glued it to the inside of the box.
Router out a notch on the front inside of the box for the locking pin to slide into.
Before final assembly lightly wax the dado's in the top and the tumblers to ensure easy movement.
Step 11: Setting the Combination
So on the top of the box there are four rows of nine squares, which basically represents four rows of numbers 1 to 9. I decided not to put any numbers on the top, so as not to give any indication that a combination was required to open the box.
Looking at the side of the tumblers pick your combination ( example 1,9,3,6 ) insert a magnet into the correct tumbler hole ( no glue !! ) and use another magnet to hold it temporarily in place. Place tumblers in dado's ( bolt removed for clarity ) Replace cover plate and put bolt back in, remove the holding magnets. The combination can be changed by removing one of the cover plates and moving the magnets in the tumblers.
Test and test again before you glue the bottom in !!!!!
After everything works, disassemble and finish all of the pieces. I gave it two coats using a wipe on beeswax and orange oil finish.
Step 12: Conclusion
I had a lot of fun figuring out the mechanics for this project and the build at times was very challenging. I looked on line for something like this but was unable to find anything remotely similar. I hope my explanation did not get too long and was clear enough to follow.
One thing I can not stress enough is check and recheck the polarity on all of the magnets before you glue them in place !!! Things don't work so well when the magnets repel each other when they're suppose to attract.
Cheers : )
Finalist in the