This simple to build spool rack can be used to store many rolls of 3D printing filament, or other similarly shaped spools (there is some copper wiring also in the pic). You could even use it as a funky bookshelf if you want!

It can hold about 28 3" wide spools as shown.

Step 1: Materials and Tools

To build this rack you will need the following

Materials

2 boards sized 1x12x48"
4 dowels sized 3/4" x 48"
Wood Glue

Tools

Drill
3/4" Forstner bit
Jigsaw
Sandpaper
Handsaw for cutting dowels
measuring tape
pencil

For the boards I chose some laminated pine from my local hardware store, which was already the exact size I wanted, and fairly cheap.

Materials cost for me was about $36, plus $8 for the forstner bit.

Step 2: Dowel Hole Layout

Now its time to start measuring and marking your boards for where to drill and cut.

Inspect boards

Inspect each board and decide which side you want to be facing outward. Arrange the boards so that any knots with wood filler or other blemishes will be towards the inside, near the bottom or toward the rear.

Once you have decided how they will be arranged, begin marking positions for the rod holes on the inside face of the boards.

Decide tier spacing

This rack is designed with 4 tiers, on a 48" board. 12" spacing between tiers leaves 12" extra board length which is split evenly, leaving 6" on top and 6" on bottom. You could do your even squeeze in 5 tiers if you wanted, with 10" spacing, and 4" extra on top and bottom. A smaller desktop version with 2 tiers could be made using 1x8x24 board.

Mark vertical positions

Measure and pencil a mark at 6", 18", 30", and 42" from the bottom of the boards. Do this twice, with the tape about one third of the way from each side edge.

Decide horizontal spacing

Most filament spools are 7 or 7 1/2" diameter, but some 1lb spools are as small as 5" diameter. I decided that 4 1/2" spacing (center to center) would work well to accomodate any spool size.

So, with 12" wide board and 4 1/2" spacing the dowels would be 3 3/4" from the edge.

Mark horizontal positions

Now, using your two marks at each vertical position to align your measuring tape, measure 3 3/4", and 8 1/4" from one side of the board. Draw a cross at these spots where you will drill the dowel holes.

Step 3: Drawing the Curves

For the radius on the top and bottom of the boards simply use a spool of filament as a guide!

Align your spool flush with top and side simultaneously. Hold the spool firmly in place and trace your curve. Do this for the other side.

For the bottom, measure the center of the board and place a mark, then line up the center of your spool with the board edge and this mark. Hold the spool firmly and trace your half circle.

Step 4: Cut the Wood

Dowel Holes

The forstner bit I used had a cutter that was about 1/2" deep. So drilling until the top of cutting head was just flush with the board meant it would make a hole that wouldn't poke through the other side. Go slowly to get just the right depth. If your cutter is longer, you can try marking the bit with tape or permanent marker to show at what depth to stop. Try to keep the holes as straight and perpendicular to the board as possible.

Jigsaw

Now using the jigsaw, slowly follow the curves you traced. Try to leave a small gap away from the lines to avoid cutting too far. Any extra bit of wood can be sanded down afterward to make the curve smooth and right on the lines.

Sanding

Sand your curves smooth and also give the rest of the board a slightly rounded edge. (Picture with drill bit shows already rounded edges).

Dowel Rods

Cut each dowel rod in half with a handsaw or miter saw.

Step 5: Put It All Together!

Dust off your boards, make sure all the wood chips are out of drilled holes, and coat the insides of each hole with wood glue. Also put a light coat of glue on the ends of each rod.

With one of the boards lying flat, place the dowels into the holes. Twist them in firmly until you are sure they are hitting the bottom of the hole. Hold the other board just above the dowel ends facing up, and line up the dowels with the holes. This step really helps to have someone else give you a hand so one lining up the dowels while the other holds the board in position. After lining up push the board down onto the dowels. Press everything firmly together, it may help to tap the with a rubber mallet or the bottom of your fist.

Stand the project on its feet, and place on a flat surface. Loading it with spools will help ensure the feet stay planted flat while the glue dries. Since it may wobble side to side a bit before glue is set, check that the rods are square with the boards and adjust if necessary. Allow glue to dry overnight.

Its done!

Once the glue has set up, you can add some stain and varnish or other sealant as desired.