Octagonal box with 45° box joints

I had this idea of making a wagon deck with 45° corners, and box joining these corners with my box joint jig.


I stacked two 7 1/4" blades to get a thicker kerf, and worked out that the 31-tooth gear against the 12 tooth gear on my box joint jig gave the right fit for use with the kerf from those two blades.


I cut the boards at a 45° angle, using my old table saw. That way I could go back and cut miters while leaving the set-up on my main saw untouched.


The best way the boards would fit in the box joint jig at a 45° angle is like this. But that would require the blade to cut "out of" the grain. That orientation makes it difficult for the saw's teeth to grab the fibers, so saws work very poorly in that direction.


Saw blades work much better with the teeth going into the end grain, so orienting the wood like this is much better.


I made a board that fits into the box joint jig at a 45-degree angle. The board has a V-groove to fit on the top edge of the jig and a small notch in it at the right side for an F-clamp to pass through.


Two screws hold the board in the jig.


Two clamps hold the workpiece in the jig. This reduces the risk that the workpiece will twist out of the way from the force of cutting.


Then cutting the joint. I could have tried stacking two workpieces in the jig, but this was a tricky set-up and I didn't want to add more complications.


Then cutting the short corner pieces to length and cutting a joint in the end of one of them. The short pieces are made of mahogany to contrast with the light coloured ash wood for the other pieces.

I used a strip of wood to brace the workpiece against sliding back in the jig.


First test fit.


So far, going clockwise around the box, I had cut all the second, or right hand side joints. None of the pieces were cut to final length yet, so if I screwed up, I could just cut the board shorter and re-cut the joint.


Next I had to cut the boards to final length. I used a clamp to hold the short pieces while cutting them.

I'm using the sled "backwards" because this table saw tilts left, which would cause it to tilt into the sled in its normal left-side position. Putting the sled on the other side avoids that.


Then cutting the joints on the other end. This required re-aligning where I cut the fingers to make sure they meshed with the fingers I already cut. Normally, when making boxes, I always place the stock in the jig so that what will be the top edge of the workpiece is at the right edge of the jig. But with these 45° joints, I have to orient them bevel down, and that means the second joint in each piece had to be oriented with the top edge facing left.

I lined these up by taking one of my initial joints, placing it in the jig with the fingers down but the top facing left (bevel up), and lining up the blade so it would cut where a finger was. I used that as the first cut position and indexed the rest off of it.


Test fitting it all together.

Two of the joints in the mahogany were too messed up, so I made two new pieces to replace them, but then I messed up one of those. Rather than make yet another new piece, I decided one of my original messed up pieces was still salvageable.


Gluing it together. I smeared glue on top of the fingers and let gravity pull the glue into the joint.


Checking that the two 45° joints add up to 90°.


I glued one joint at a time and let it dry before adding another piece, until I had two halves assembled. Once the glue was dried on those, I mated them together.


I ended up using some clamps to press the final joints together.


I had some slight misalignment of the boards in the end, so I used a hand plane to level all the boards...


... then made the other edge parallel on the table saw.


I used my edge belt sander to clean up the box joints. Some of them had quite a bit of protrusion, so I flatted some on the bandsaw first.


Adding the 45° corners to the box doubled the number of joints I had to make, and at least tripled the work of making this box due to added complexity. It looks nice, but I'd recommend you think twice before making an octagonal box! In this instance, cutting corners didn't save me anything!

I made this box as a starting point for new deck for a kid's wagon that I built. I'll have more on that next week.


See also:

More about box joints

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