Recently I developed some software to assist in making box joints on a router table using a simple pivoting fence. The software prints out a custom template for setting the free end of a pivoting fence. Unlike the methods that utilize a guide pin to set each slot position from the previous slot, this method has no cumulative error. And a pivoting fence is a lot simpler to make than a parallel-moving fence indexed by lead screws. I have found it particularly useful to print several templates with slightly different pitches to fine tune the tightness of the box joints. I would appreciate comments on my software. It is available on my website at
By the way, if you don't want to try the software, at least look at the pictures in the manual, also available from that web page. It shows the setup and a sample box joint that was made using that method.
Looks cool. It took a bit of re-reading to figure out what each of the parameters actually did, but eventually it all made sense.
I wonder if you could get a more accurate starting point by doing a few cuts with the actual bit in a scrap of the project wood and measuring it with calipers...
Personally I like idea of the dovetail jig template with the adjustable-diameter bushing. I've never actually used one though, and it's definately more expensive...
There are several ways to get an accurate starting point, and the way you suggest is certainly a good one. I assume that by setting the starting point you mean deciding exactly where to tape down the template. Because once you tape down that template, all the slot positions are determined. Of course moving the template is very easy if you use masking tape and want to make some fine adjustments to the offset.
The setting of the starting point is actually not a critical parameter. If the template is moved by 1 mm., then all the slots in the box joint will be moved by that same 1 mm., but it will still be a perfect box joint.
One aesthetic consideration is the size of the top and bottom fingers in the box joint. If the width of the wood is not an exact multiple of the slot spacing, then the top and/or bottom fingers must be partials. That can look OK if the partials are 1/2 to full size. But if a partial finger is too small, it looks like a mistake, and it might even break off during routing. Fortunately there is usually a starting offset that will ensure top and bottom fingers are of substantial width. Or I suppose you could adjust the dimensions of the project to match to the nearest multiple of the slot spacing. But that seems like an unnecessary concession to have to make. You can see that the sample box shown at the end of my manual has partial-width fingers at the top and bottom.
There is a limit to how far you can move the template, though. Theoretically, there is only one right place to tape the template to the table and still have all the tick marks on the template fall exactly in line with the edge of the fence. But in practice you can move the template a little and still get good results. If you move it so much that the tick marks are not exactly parallel to the edge of the fence, then you can simply pay attention to where those tick marks cross the X-axis base line, and position the fence so the desired intersection point is just at the edge of the fence. If you want to make larger changes in the offset, instead of moving the template, it would be better to print out a new template with a different "Router Offset" parameter. It is not necessary that the Router Offset parameter be exactly half the diameter of the router bit. Doing so just makes it easier to position the template by adjusting the fence to just kiss the router bit and then sliding the template under the fence until the "0" line lines up with the fence edge. But if the Router Offset is set to slightly different number, you could still use the bit to position the template. You would just use a spacer or gauge block or use calipers instead of having the bit just kiss the fence. That is why the parameter is labeled "Router Offset" and not "Bit Radius", even though in many cases that's just what it is.
No, actually I meant as a value to input for the "tick mark spacing" since it is dependent on the size of the slot cut by the router bit. (The same holds true for "router offset" to a certain extent, with the caveats from your email.)
Your manual has a section on how a worn 0.25 inch bit actually cut 0.241 slots. I was simply suggesting making some test cuts to see what the router bit actually cuts instead of proceeding by trial and error.
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