The first time I ever saw a box joint jig guided by a template bearing was six or seven years ago when a friend showed one as a club demo. His jig was a simple plywood sled with a fence, a wooden bar for spacing the fingers, and a slot through the base that fit a template bearing guide. If I remember correctly, his made joints with 3/8” fingers. Shortly after his demo, I made the smaller jig shown below for 1/8” ‘fingers on small drawers.
Here’s a photo of a jewelry chest drawer I recently made with this jig.
I made several modifications to the original design on this small jig. For the spacer I used 1/8” square steel ‘keystock’ since a 1/8” wooden spacer would be easily bent or broken. The keystock was routed into the bottom of the piece behind the fence – with a slightly wider slot in the fence itself. Loosening the screws that fasten the fence to the base allows minor spacing adjustments. I also cut the template guide slot a little over half way through the ½” base – cutting the rest of the way through with a 1/8” router bit. This narrow slot in the top of the sled provides a more solid area for both guide and workpiece – and combined with an upcut spiral bit, also helped produce a cleaner cut.
More recently I built a similar – but larger – jig for making joints with both ¼” and 3/8” fingers. My experience with the smaller jig led me to make further improvements to the larger jig as described below.
For these larger fingers, I could have use wood as a spacer, but since keystock was relatively inexpensive and not subject to swelling or warping, I decided to use it on this larger jig as well.
The fence and the adjustment system on this jig are quite different. On the newer jig, the fence fits snugly into a ¼” deep groove in the base. This keeps it perpendicular to the guide groove, and allows the fence, fence bracing, and spacer all to be fastened together and moved as a single unit.
The first photo below shows the overall jig, and the second, a closeup of one of the fences and it’s bracing.
This new jig is 12” wide x 16” long, and made from phenolic-coated plywood – with a fence at each end. One fence is used for joints with ¼” fingers, and the other for 3/8” fingers. The guide slot is 5/8” throughout, but the slot through the top at each end was made by the bit to be used there.
The first picture below shows the guide bushing, and the latter two show what the bottom looks like.
In the photos above, the flush stops at each end of the guide slot are simply glued-in strips of hardwood to limit travel of the router bit and control air flow. The stop in the middle also helps restrict the travel of the bit, but its primary purpose is to help with the air flow on the dust pickup described later. The latter picture above, although distorted, helps illustrate the guide slot, the stops, and the ‘through’ cut matching the 1/4” and 3/8” bits. It also shows the clamping screws used when making minor adjustments. Putting these clamping screws in the bottom was simple, but flipping the jig over while adjusting – and remembering to work in ‘mirror-image’ turned out to be a pain in the neck. Friends who have made jigs based on mine followed my recommendation that their clamping screws be located in the top. If I ever build another, that’s were I will put mine.
Since even the mini jig creates a fair amount of sawdust, I decided to experiment to see if I could pick up a good portion of the dust on the new jig. The 1-1/4” holes between the angled fence braces fit an adapter to my shop vacuum. These holes (one in each end) connect to each guide slot through concealed cavities behind the fences. I was very surprised at how well it works – removing about 90 to 95 percent of the dust when making 1/4” joints – and about 70 to 75 percent when making 3/8” joints. It’s important to realize that the guide slot must be deeper than the height of the guide bushing for the dust pickup to work. In my case, the top of the guide bearing is a about ¼” above the router table top, while the guide slot is about 3/8” deep.
Regular straight bits will work on this jig, however they put more sawdust into the air, and also cause more splintering. Actually, the up-cut, solid carbide router bits I use, combined with the zero-clearance slot virtually eliminates chip-out. In case ‘upcut’ sounds wrong, it’s because the term relates to hand-held routers – rather than table-mounted. Just remember the ones to be used with this jig are those that pull the chips toward the router. An unexpected ‘bonus’ of the dust system is that the vacuum helps hold the workpiece snugly against the fence.
Another thing I should mentions is the need to use an accurate guide bushing. When I first made the 1/8” jig, I was unaware that the aluminum bushings I had were ever so slightly ‘out-of-round’. When that’s the case the fit of the joint will depend on the combination of the direction in which the guide is mounted and the direction the sled is pushed across the guide. For that reason, on the new jig I used a precision template guide bushing made by Whiteside as shown in the photo above. It has a perfectly true, 5/8” outside diameter with a center hole large enough to accommodate both ¼” and 3/8” bits – plus it comes with a centering pin. With a good up-cut bit, accurately centered in a true guide bushing, the only adjustment that should be necessary when the jig is used again is to verify that the bit is still centered. As a matter of fact, with everything set up accurately, it will also make no difference which direction the sled is pushed across the guide.
Like any other good jig, accuracy in construction is essential. The guide slot must be straight, perpendicular to the fence, and accurately fitted to the guide bushing. Before any cuts with the router, the bit must be accurately centered – etc. If a router bit provides an accurate fit to the guide, it could be used to cut the guide slots, thereby creating integral stops, and eliminating the need for separate ‘inset’ stops. Instead, I chose to use a stacked dado set to cut my guide slot.
Another advantage of this jig is portability. I use mine on both my small router table (described in an earlier post) as well as on my larger router mounted in the table saw extension. I can, in fact, use if on any other table-mounted router that accommodates P/C inserts.
The final photo below is a close-up of a test sample of a joint with 1/4” fingers. Incidentally, the accuracy of this jig lends itself well to the technique of dry-fitting the joints and using thin ‘super glue’ to wick into the joints. It’s much easier, and holds exceptionally well. The only caveat is to try to avoid too much glue wicking into the inside corners. I hadn’t realized until I proof read this blog that the fingers on the photo below appear not to be flush with the sides. Let my assure you that’s simply an optical illusion I can’t explain.
I’ll be happy to respond to any questions or comments.
-- Dave O.