I have received countless emails and messages about adapting the Lynn Sabin Box Joint Jig to the router table, and that is what this article and video are about.
Some time ago, I made a video using the Lynn Sabin plans that are available on sharkguard.com, very kindly provided by Lee Styron ... thanks Lee, for doing this. The Leeway Workshop LLC provides quality safety devices for table saws, like Shark Guard, splitters and riving knives. The link to specific plans is further down this article.
The plans, as I understand it, were originated by Lee Sabin for use on a table saw, using single blades, dedicated box-joint jig blades, such as Freud Tools, or using a stacked dado blade set-up. If you have never made this jig before, it is best to read these and the instructions provided with the plans, before you begin.
This jig works great on the table saw using dado blades, unfortunately, dado blades are not available in most European countries. I understand it is not illegal to own them but it is illegal to sell them. The plans I used are basically identical to those provided on the sharkguard.com website, with a couple of small alterations.
For everyone who is on the metric system, you will have to do all the conversions yourself. I do not know what router bits sizes, or threaded "ready-rod" types you have to work with. All the components I used were Imperial.
The way this jig works is based on the the "ready rod". I used a 16 threads per inch version. This means that if you have a nut on a rod like this, and turn the rod 16 times, it will advance that nut one full inch. Converting that to a 1/4" box joint, from the start position, you make one cut, turn the rod 8 times and that will advance the carriage 1/2" inch which means the second cut will leave a 1/4" pin, then make the cut at the 1/2" mark, and so on ... thus making the beginnings of the box joint cuts.
For making my jig, I used the plans as they were provided, which state that all parts should be 3/4" material. I recommend good quality plywood such as Baltic Birch. I used what I had available for demonstration purposes only. The only difference was that I used 1/8" material for the base because I felt 1/4" might limit the amount of height I could get with some router bits. As it turns out, 1/4" would probably have worked fine.
The first thing you will want to do is ensure you have all the parts needed, but the metal and wooden parts. The specific plans and instrucions are at http://www.thesharkguard.com/lynnjig.php
You will need ...
1 - 3/8 x 16, make sure it is long enough.
1 or 2 - matching "T" nut for this rod
1 - large flat washer 1-1/2" outside diameter that will be used to lock-down the "T" nut
3 - hexagon nuts that also fit the ready bar
2 - flat washers
2 - lock washers
1 - crank (make your own with some mild steel and some hardwood doweling)
1 - UHFW - 3/4" plastic runner (purchase or make your own)
It is important with this jig to cut all the pieces as accurately as you can. Slight variations in assembly or materials can mean your box joints do not fit together tightly. Make sure you take a moment to dry fit the parts as you move through the cutting and assembly. Any part of this jig that does not move smoothly or fits together too tightly can affect your outcomes.
Remember - 3/4" plywood is NEVER 3/4" thick. This is done by design, it is not poor quality plywood.
After you have cut out all the wooden parts and done dry fits, next is assembly.
one of the critical issues with building this jig is to have the carriage run as smoothly as possible. This means aligning the holes on the sides or the jig and those on the carriage. In my assembly, I used a parallel board to ensure the carriage was aligned absolutely parallel with the front of the jig, I am not sure this amount of accuracy was needed. If you drill the holes as the plans call for, and use quality plywood the carriage should align just fine.
An more with the carriage holes ... the the hole that will be used for the T-nut will need to be slightly larger than the other holes. Drill this hole after all the other holes are drilled, or use a file or rasp to enlarge it.
When installing the T-nut, I used some longer screws to make sure the T-nut was inserted as best aligned with the other holes as is possible.
To install the ready-rod, I first put one self tightening nut about an inch from one end of the rod. The assembly or the rod should look like this ...
- nut, lock washer, crank, self-lock nut, flat washer, outside frame, flat washer, hex-nut, lock washer, nex-nut, T-Nut -
It's important that the nuts be somewhat snug that are holding the ready bar to the frame. Too much slop will create problems with fit.
The final part of assembly is to use some UHFW plastic for the Mitre slot. The positioning of the jig in relation to your router table will depend on where the mitre slot is located. there is no standard for this you will you have to think about the positioning of your jig in relationship to the router bit that will be cutting the joints. You will need to leave as much room as you can on either side. The best guideline I can give is to position the carriage about the middle of the jig, then align the carriage, by eye with as close to the center of the router bit. Where ever the jig is sitting over the mitre slot is probably the best position for attaching the plastic runner.
Router Bit Considerations
You will need a 1/4" router bit to make this jig usable. There are 2 basic kinds of router bit available, carbide tipped and pure carbide. They are often priced about the same price. For this kind of jig, the carbide tipped is best. That is, a steel router bit with carbide edges. Pure carbide bits will work, but are not ideal for this application as carbide is very brittle and if you push too hard, or happen to hit a knot while pushing the bit, there is a good chance the bit will snap. Carbide bits are better suite to plunge cutting, not lineal cutting.
Joints Too Tight
It is not uncommon for these kinds of jigs to make accurate, and tight joints ... sometimes the joints are too tight, especially when it comes time to gluing. One thing that can help a lot is to run a metal file through each slot, one time. These files can be purchased new, or used many places and if you choose a coarse one that is 1/4" thick, it is perfect for easing the tightness of joints without compromising the a nice snug fit.