How to Build the Ultimate Stackable CrossFit Jump Boxes
I have a friend who loves working out and wanted to be able to do more CrossFit type workouts at home. She asked me if I would be able to make her some jump boxes. She had searched around online and everything she found either looked cheap or was really expensive. She wanted to be able to adjust the height (in accordance with specific workout or level of motivation) and liked the options that could be rotated to offer two different heights. We ended up with something a little different and here is how I made it…
Creating the Design
I did some searching and started playing around with different concepts. I liked the idea of rotating the box to offer a different height, however the height difference couldn’t very significantly without causing the box to be awkward and/or unstable. After modeling a number of ideas and reviewing them with my friend we settled on a three box, stackable design. With the stackable design she would be able to configure the boxes into six different heights. I played with the design, tweaking dimensions until it could be made from two 4’ x 8’ sheets of ¾” plywood. The layout and dimensions are available in Stackable CrossFit Jump Box Plans.
I bought the plywood from Home Depot and had them cut the sheets down based on my layout. This made the plywood easier to transport home and down into my workshop. I then cut the various pieces from the plywood sheets with my table saw (you could also do this with a circular saw and straight edge, or even a jig saw if you take your time).
To make the boxes easier to lift and move around I wanted to add handles. I looked into some folding metal handles but decided to keep it simple and just cut handle holes into the sides of the boxes. I made a template for the handles in a piece of hardboard and traced the outline onto the boxes. I drilled large holes inside the traced lines and then used my jigsaw to remove the rest of the material, making sure to stay inside of the lines. Once the majority of the material was removed I lined up the template with each hole, clamped it in place, and cleaned up the edges with a large trim bit in my router.
Cutting the Joints
Next came the most difficult and time consuming part, cutting out all the notches.
The boxes you can buy online are all built with the edges butting up to the inside face of the adjoining piece. Most of them are then screwed together. While this construction method is the easiest way to build a box out of wood it is definitely not the strongest. Since these would intentionally be taking a beating I wanted to make sure that they would be robust. So I designed them with notches on the edges that interlocked to provide more surface area and lateral support for the joints.
My initial thought was that I would carefully cut out one set of notches using a jig saw and then use that as the template for the rest of the pieces. I planned to use a large trim bit in my router and just follow the template like I had with the handle holes. While this was a great plan in theory, it wasn’t very effective in execution. After playing around with a few alternate methods I found that the most effective way to cut the notches was with my bandsaw (jig saw would also work fine if you take your time). I cut all of the edges of each notch. Then I cut in at an angle from one edge of the notch to the opposite bottom corner flipped over the piece and cut from the other side to complete the notch (probably easier to just watch).
After cutting out 228 notches (it actually went pretty quick once a got into a rhythm) I dry fit everything together using a file to adjust a few of the notches for a better fit. Next I glued blocks in the corners of the top and bottom pieces to support the corner pins. The blocks were made from two 3.5″ pieces of an 8′ 2″ x 4″ glued together.
I was happy with the fit and moved on to gluing the boxes together. I used a silicone glue brush to spread a thick coat of wood glue over each face of the notches, one side at a time. Once fully assembled I used just about every clamp in my shop to ensure that there wouldn’t be any noticeable gaps.
Making the Pins
While I was waiting for glue to dry I made the corner pins for stacking. To do this I cut 4” lengths from a 1-1/4” dowel. I rounded both ends of the pins with a ¾” round over on my router table using a jig. To make the jig, I drilled a 1-1/4” hole through piece of 2×4 and slightly oversize hole with sandpaper. Then I drilled another hole intersecting the first for the router bit. I aligned the jig with the bit on my router table and clamped it in place. I inserted each end of the pin into the hole and rotated it to route the edges. You could also round them over with a sander.
Sanding, Drilling, and Filling
I intentionally made the notches slightly deeper then the thickness of the plywood so the tabs would sit proud of the surface once assembled (always easier to remove wood then to add it). I used my belt sander to make all of the tabs flush to the surface. With the surface flat I moved over to the drill press, and with a forstner bit, drilled a 1-1/2” hole 2-1/4” deep in each corner (slightly larger than the diameter of the pins and a little deeper than half the length of the pins).
I used a ½” round over bit in my router to soften all of the edges around the box, handle holes, and pin holes. Then I filled all of the small gaps and chips with wood filler. A few hours later I used my random orbital sander to smooth out the surface and remove the excess wood filler.
The Finished Product
I dropped pins into the holes of the boxes and stacked them largest to smallest to test it out. The design worked as well as I had hoped. I tried out all of the different configurations and was pleased with how easily they went together. Though it is worth noting that lifting the boxes can be a bit of a workout in itself since 3/4″ plywood is relatively heavy. The handles are definitely helpful and worth the extra effort.
Other Design Considerations
There is a lot of dead space inside the boxes, especially the largest box. If space or organization is a priority for you it may make sense to turn one or more of the boxes into a storage vessel so it can serve double duty. Possibly a great place to store free weights, bands, boxing gloves, or other workout equipment. One possible storage option would be to leave the top free floating by not gluing it in place. Another option would be to cut the box in half after it is assembled and install trim pieces around the inside edge of one of the haves for alignment and then installing latches or clasps to hold the haves together. Or you could also use hinges and latches. Just a thought… if you have any other ideas or suggestions please share them in the comments below.