A friend recently had me build some wooden boxes for his crossfit workouts. Crossfit is a fitness program where you do a variety of movements that exercise multiple muscles at once within a short amount of time. When used as part of a crossfit regimen, ordinary wooden boxes become plyometric or “plyo” boxes, that provide an intense workout. How do you use them? You jump on them to develop strength, speed and explosiveness.
He had me build 2 large boxes (measuring 30-inches x 24-inches x 20 inches), and one smaller box for his daughter (20-inches x 16-inches x 12-inches). The different sizes of each box’s sides provide three different heights to jump on.
I determined to build the boxes from 3/4″ high-grade hardwood plywood. I would router out a 3/8″ x 3/8″ notch on all 4 inside edges of each side. These notches would allow each side to be overlapped to the adjacent side making the joints stronger from both directions. Notching the edges would also allow for more glue surface area at each joint (also adding strength). Here’s a sketch of a large box with the top and bottom removed to show the notched edges forming the joints:
Here’s a diagram showing the actual dimensions of each side of a large box that accounts for the 3/8″ notch and overlapped joints so that the finished box ends up exactly 30″ x 24″ x 20″.
I started by cutting all the plyo box sides from 3/4″ birch plywood using my table saw. To help me make the cuts I made a make-shift support for the heavy sheets of plywood using the coffin I made for Halloween a few years back, an old piece of laminate countertop, and some other scraps I had around. Pretty ghetto I know, but it got the job done helping make the cuts as accurate as possible.
Once all the sides were cut out, I routered the inside edges of each piece. This required two 3/16″ deep by 3/8″ passes with my router. Having a router table really helps with this step.
Here’s a shot of the notched edges after the first pass:
After the second pass through the router, I used a hole saw to drill a couple holes in one side of each box. Then I used a jigsaw to remove the plywood in between the two holes to form the box “handle” or “grip”. I used a round-over router bit to remove the sharp edges of the handle. Then I sanded these smooth.
Then I laid out the sides of the box on the floor and put some wood glue on all the notched edges:
I used some straps and some finish nails to hold the boxes tightly together until the glue dried:
Next, I used my router with my round-over bit to smooth off all the outside edges of the boxes. (Otherwise, I imagine you could get a fairly nasty cut on your shin by slipping off during a workout).
These boxes don’t really have to be that pretty, but I went ahead and puttied the nail holes and any minor voids in the joints with natural wood filler. Then I sanded all the boxes smooth.
My friend used a stencil to spray paint numbers on each side showing its height:
Of course I figured you’d want to see a little footage of how these boxes are used…
DIY Material Cost Breakdown for 1 Large Box:
- 4′ x 8′ x 3/4″ birch plywood $48
- wood glue $5
- finish nails $2
- natural wood filler $5
- sand paper $4