Box Joint Jig

I want to make a tiny wooden box for another project that I have going on the back burner and I’d like to use box joints for the construction to make it strong and to look a bit fancy.

There are loads of videos on the Intertube showing how to make simple pin based box joint jigs, through to incredible feats of engineering from Mathias Wandel and John Heisz that would take me several years to make. Yes, I know my place on the woodworking spectrum so it’s a pin based jig for me. I referenced the two videos below by Steve Ramsay of Woodworking for Mere Mortals and David Picciuto of “Make Something” to make my first jig of this kind.

I won’t go into much detail because the guys’ videos above detail exactly what I have done but the main points are below.

I already had a couple of pieces of 15mm MDF offcuts from a build last year. They are a little lower than I would like and means that the jig can only be used safely with clamps - no handheld workpieces here!

Similarly I already had some strips of white deal sitting around that were just a little thicker than the kerf of my CMT flat tooth saw blade, so I grabbed one of these and sanded it down to made the kerf width. The saw blade is a narrow diameter, 4mm grooving blade that I picked up from J.Jacksons in Kilcoole, who are an unsung family business providing great customer service in Co. Wicklow.

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I laminated two of the MDF boards together for a sturdy but arguably short fence. Then drilled two vertical holes in the top to receive the bars of two UJK fence clamps, with a red oak stop to ensure I could replace the jig on my mitre gauge in the correct position each time it’s fitted.

It’s here that things went a bit skew-ways. The fence clamps couldn’t be properly tightened because the mitre gauge fence extrusion is too light and the MDF fence cannot be fitted directly to the mitre gauge because the gauge doesn’t have passthrough screw holes - thank you Bosch for that non-standard piece of gauge design. As a result, the whole rig kept moving slightly during my test cuts, ruining the joint every time.

I decided to remove the oak stop block and replace it with two metal clips that would engage with the t-slots on the mitre gauge fence only for the screw heads to sheer off not one but both of the screws holding it in place!

This was my fault for using junk screws that came free with some walk plugs but in my own defense, it’s for a jig and I didn’t think they’d ever need to be removed :D

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At least the junk screws were so soft that the bandsaw cut through them like butter. I cut off the stop block completely, flush to the MDF and used a punch to drive what was left of the screws below the surface and left them there. Then I positioned a metal clip inside the t-track at each end, re-adjusted the fence position relative to the blade and performed some more test cuts with better results. This makes the jig look simpler and I’m still throwing one hand clamp on to it for extra stability, which I check for tightness between every cut.

It’s a flawed jig because as soon as I remove it from the saw, it will need to be completely set up from scratch. That said, it is ready for me to make the box that I want to make, so I can go ahead with that.

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Unfortunately making this jig shone a light on the one significant design flaw in my jobsite tablesaw. Both of the mitre slots and the sliding table have excessive play, which results in a visible difference in cuts at anything finer than construction framing levels of joinery. Unfortunately the fixes to the saw for this problem are non-trivial and require an accurate drill press, which my Parkside cheapo is not!!

Another option is to completely avoid the issue by updating the jig with a dedicated sled and homemade mitre runners, which is exactly what I’ll do in the spring.