Introduction: Compass Table
One day I was playing around with a compass and a magnet noticing how much fun it was to manipulate the compass rose as I moved the magnet around. I'm of the mindset that when it comes to fun, more is usually better, so I rounded up 500 compasses and some rare earth magnets and decided to turn what started as just a little silly but entertaining play time into an actual piece of furniture.
The compasses are inlaid into a custom table top underneath a piece of glass. The coasters were made to match - they also provide an inconspicuous home for the powerful rare earth magnets that affect the compasses.
Now I always know which way is north, and exactly where my cup of coffee is...er, so long as it's always on my compass table.
**Note, the reliability of compasses in mass quantities and close proximity decreases somewhat since compasses themselves are magnets. It still works, and actually results in some pretty cool patterns, but if you're looking for the table to be 100% accurate, I'd recommend not designing a table that places them so closely together. I'm a big fan of the way the table came out, as it's a toy just as much as it about the science of magnetism.**
Step 1: Materials
- 12mm sanded plywood
- table legs - I used 4 Ikea Vika Oleby prefab legs
- 16 7/16" x 1/8" thick glass circular top (I had this custom cut)
- a couple square feet of 6mm sanded plywood
- 2 cork coaster inlay
- 2 rare earth magnet
- approximately 500 "mini compasses". I got mine for around 20 cents a piece off Ebay. It takes 500 20mm compasses to cover a 16.5" circle - crazy I know!
- circle jig
- wood glue
- polycrylic - water based clear satin wood finish
- speed square
- random orbital sander
Step 2: Modify the Legs
The Vika Oleby legs from Ikea look cool and aren't *too* Ikea-trashy, so I saved myself some building time and went for them. The circular table that I built is a bit too small to fit them all on there in their store-bought form so I modified them slightly.
Using a speed square I marked and cut two 45 degree lines on the end of the table leg where it mounts to the the table top so that I could fit 4 legs on my 18" table top.
I removed about 1.5" of material off the corners...no need to be precise here so long as you don't affect the mounting bracket.
Step 3: Route Out the Tabletop
The table top is made from three different layers of 12mm sanded plywood in order to get the right depth for the compasses and overall table top thickness.
Two 18" circles were routed out using a Jasper Circle Jig (a tool that I'm quite fond of). A third circle of the same size was cut, and then had a slightly smaller circle inscribed inside of it to create the rim for the table. The rim turned out to be 1/2".
Step 4: Glue and Clamp
I used a brush to spread some wood glue between the layers, stacked them all up centering them carefully, and then clamped and weighted the entire sandwich between some stiff maple boards until they dried.
Step 5: Sand and Finish
Once the glue dried I used a random orbital sander with some 220 grit paper to smooth everything out and take off any rough edges.
Then, I brushed two coats of polycrylic, a Minwax brand water based clear wood finish, that's a whole lot easier to clean up and is more forgiving than Polyurethane onto the table top.
I sanded lightly with 220 grit paper in between the two coats for a nice smooth finish.
Step 6: Attach Legs
With the table top finished, it was time to mount the legs onto the table.
Using the supplied mounting brackets as a guide, I marked and drilled the mounting holes for the legs into the top.
The supplied Ikea allen wrench tightens the bolts into place.
Step 7: Arrange Compasses
If the table were a square or rectangle I would have arranged the compasses in a grid, but since it was a circle (to match the circular form of the compasses themselves), I had to come up with other arrangement options. After fiddling around with them for a short while I was able to find something that worked well - concentric circles.
Arrange the compasses as tightly as possible working from the outside in, getting the final few in place takes a bit of a massaging, but once they all go down, it's a nice symmetrical tight fit that can adjust to whatever size circular table that you have.
Step 8: Coasters - Route Out
The coasters are made in almost identical process to the table top itself...just smaller.
One base circle was cut from the thinner 6mm plywood and then one ring was created to become the coaster lip. The ring is a bit more tricky to route then it's big brother was with the circle jig because it doesn't have enough friction to hold it self in place as the router passes by. A little tape does the trick so that you can complete the cut.
The rare earth magnets that I bought were 3/4" by 1/8" thick, so I routed out a small inset for them in the coaster base using just my eye, since that hole was going to get covered up anyway in the next step with the cork coaster pad.
When you lay the magnet down in its pre-cut hole, make sure that you've got the pole facing the right way, we want to attract the north end of the compass, so flip it around until you've got it the right way.
Step 9: Coasters - Glue and Clamp
Spread glue on the rim of the coaster and the coaster base and make a coaster sandwich. The cork pads can be cut, or, pre-bought from Ikea as well and glued into place inset within the rim in order to cover the exposed rare earth magnet.
Clamp them between some of those pieces of maple from before and allow them to dry.
Step 10: Coasters - Sand and Finish
Once the coasters were dry I sanded them smooth with some more 220 grit paper and put two coats of polycrylic on them as well.
Finding things to dry them on is easy since they've got a magnet embedded in them...
Step 11: Glass Top
I was toying around with the idea of pouring epoxy or polyester resin into the table top to finish things off and permanently secure the compasses into place, but upon learning more about the process, I decided that cutting a simple glass top would be safer since I didn't want to jeopardize my 500 compasses in case something went wrong with the resin pour.
I got the glass cut at East Bay Glass at exactly 16 7/16" so that would perfectly fit inside the rim of the table. It sits directly on top of the compasses nicely and has virtually zero play. As a result, I'm not worried about scratching the tops of the compasses, but if whatever you were inlaying was more vulnerable for some reason, putting in some kind of supports for the glass could be a good idea.