LumberJocks

Kerfmaker Style Box Joint Jig

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Project by Tootles posted 01-05-2013 06:58 AM 3524 views 11 times favorited 2 comments Add to Favorites Watch

I have a Triton Workcentre, which imposes a few constraints on me. One of those is that the clearance for my blade is fixed, and while it is wider than a zero clearance, it is too narrow to install a dado balde in my saw. That meant that making box joints on my saw was a problem. But a while ago there was a “craze” on LJs for making kerfmakers, and that gave me an idea. I made a jig that would mount onto my mitre guage that could be adjusted in a manner similar to a kerfmaker to position the peg in the correct place for each of four initia,l and all subsequent cuts that need to be made. Perhaps the following diagram will help to explain. In the diagram, “T” is the width or the fingers and “t” is the width of the peg.

I started by making a T-shaped fence that is bolted to the mitre gauge. This fence needs to be T-shaped so that (a) it can be consistently positioned on the mitre guage, and (b) to provide a fixed stop against wich to adjust a second, sliding fence. To allow the sliding fence to slide, the T-shaped fence has slots in it (see photo 2).

Next I made a sliding fence that includes an aluminium peg. I used aluminium for this because I could get a piece that is the same thickness as my blade, and by using an angle section, I had the ability to screw it into place from below. This fence has two bolts through it with wing-nuts for easy adjustment.

Last, I made an aluminium insert that adjusts the sliding fence position by the thickness of the peg. That was the jig complete.

To use the jig, I need two pieces of wood (spacers) that are the thickness of the finger width (or widths – I could easily use two differnt thickness spacers to get two different width fingers). Then:
  • I start by marking one edge of each piece of wood. This edge must always be on the right when standing behind the saw.
  • I remove the aluminium insert and set the sliding fence with one spacer between the sliding fence and the fixed fence, then I make one cut on each end of the side pieces, with the edge of the wood agianst the peg.
  • I insert the aluminium insert and set the sliding fence with one spacer between the sliding fence and the fixed fence, then I make one cut on each end of the front/back pieces, with the edge of the wood agianst the peg.
  • I insert the aluminium insert and set the sliding fence with two spacers between the sliding fence and the fixed fence, then I make one cut on each end of the side pieces, with the edge of the wood agianst the peg.
  • I remove the aluminium insert and set the sliding fence with two spacers between the sliding fence and the fixed fence, then I make one cut on each end of the front/back pieces, with the edge of the wood agianst the peg.
  • Keeping the sliding fence set with the aluminium insert removed and two spacers between the sliding fence and the fixed fence, I move each end of each piece of wood across from left to right, placing each kerf over the peg and making as many cuts as are required for the number of fingers in the joint.
  • Lastly, I simply remove the waste ( the rectangles shaded grey in the picture above) between the individual cuts.

So, does it work? Well yes, but … you absolutely have to keep your wits about you as it is incredibly easy to make a mistake. In fact, I made this jig over a year ago, but today was the first time that I did everything right. This is the joint that I made as a result

If anything, the joint in the picture above is too good. It is so tight that it would probably squeeze all glue out of it.

Over the period of trying to get this jig to work, there is one addition that I made to the design. I acquired two paper rulers (from a large, four-letter furniture store) that I stuck to the back of the sliding fence. The zero position of these two rulers are different by the thickness of the peg.

The idea is that I could, in theory, set the sliding fence position without needing to use spacers. I have yet to try that though.

-- I may have lost my marbles, but I still have my love of woodworking





2 comments so far

View stefang's profile

stefang

13293 posts in 2023 days


#1 posted 01-05-2013 07:53 AM

It looks like a winner! You got a great result with it. I too have a table saw that doesn’t conform to the American style machines with respect to the mouth and it also has only one slot to run the miter gauge in. This prevents me to a large extent from using many of the great table saw jig designs I find on LJ and other places. My solution was to build a jig which is adjustable for any width. That said, I have found my scroll saw to be the easiest way to make accurate box joints and dovetails.

-- Mike, an American living in Norway.

View kiefer's profile

kiefer

3186 posts in 1356 days


#2 posted 01-06-2013 04:11 AM

You got it working just fine by the look of the sample .
Great thinking ,I love solutions like this .
It’ not more too;s but more ingenuity !

-- Kiefer 松

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