ADJUSTABLE BOX JOINT JIG
Tips for building the featured jig from Shop Notes.
SHOP OWNER: Carole Valentine
LOCATION: Onley, VA
As a new woodworker, the idea of a box joint jig intrigued me, and I had looked at many plans. However, they all seemed somewhat limited in that they were only for one size of joint. Finally, I found the plans for a micro-adjustable box joint jig in ShopNotes (Vol. 2; Issue #8) and decided that was the way to go.
Since my area lacks a hardware store that carries much more than bailing twine and nails, I ordered the hardware kit for the jig from the Woodsmith Store (http://www.woodsmithstore.com/boxjoint.html). The kit, which cost $15.95, includes all necessary hardware plus a copy of Issue #8 which features the detailed plans for the jig as well as other good stuff. If you don’t need the hardware kit but want the plans for the jig, you can download them at http://store.yahoo.com/plansnow/boxjoint.html for $4.95. The plan recommends using hardwood and walnut is what I had on hand, so it was off to the jointer and planner. After dimensioning the board to a “squirrel’s hair” thicker than the called for ¾”, it was off to the sanding station. I wanted to have the board that I would cut all the pieces from at its final thickness before cutting the parts. Cutting is a straightforward process well documented in the plans… just be sure your stock is square and your tools are cutting square.
The fence is 5½” high, but you could make it a little taller if you wanted to. Use either the table saw or a router to cut the 1½” wide by ¼” deep dado in the fence for the sacrificial backing plate. I used my dado set on the table saw. One thing to note when drilling the bolt hole for the backing plate… if you put it dead center, you can flip the plate over when one end gets chewed up. If you do this, you might want to use a slightly smaller star knob than the one provided in the kit so it doesn’t hit the adjustment blocks. For the material rest, cut the ¾” rabbet (I used the router table) on one long 18” piece, then cut the moveable and fixed rests from that piece. The Grr-Ripper came in handy when cutting the fixed material rest to its final 11 3/8” x 1½” size on the table saw. The adjustment blocks require three ¼” slots. The two on the back block are open ended and the one on the front block is closed. If you want to cut them with the router, I suggest you cut the closed slot in a long 2” wide piece of stock before cutting the blocks to length since it’s easier to work with a router using a larger piece of stock. I chose another avenue… I drilled a hole at the ends of the slots and then used my scroll saw to finish them.
The metal brackets that form the key are just standard 4” mending plates trimmed to size. The plans call for one additional screw hole 3/8” from the top end of each bracket. I added an additional screw on the lower leg of the bracket on the back adjustment block that pulls it tight and flat to the ledge of the moveable material rest. Be sure and drill a straight, properly sized pilot hole for this screw since the material is only ½” thick at this point. Installing the hardware was fairly straightforward. The only thing that made me nervous was the installation of the threaded brass inserts that hold the adjusting rods. The plans fail to give the dimensions of the pilot hole for these inserts, so I fiddled with a piece of end grain scrap to find the best fit. I could have used either 7/16” or 29/64”, but since there is not a lot of stress on these inserts, I chose the 29/64” bit. If you are using a dense hardwood like maple, I definitely think you should use the 29/64” bit. The holes for the inserts and the inserts themselves must be absolutely straight for smooth operation, so use a drill press and be sure it is running square. Don’t pull the bit completely out of the hole to clear the chips and try not to run the bit up and down more than once or you will have a hole slightly larger than intended! I used a piece of 10-32 all-thread chucked in the drill press with two nuts to start the inserts straight then finished with a screwdriver. It’s important that any screwdriver you use for this fits the slot in the insert exactly. I ground an old “fat Albert” screwdriver I had lying around to fit the slot exactly. A little beeswax on the insert, especially if you use the 7/16” bit, will help with insertion.
One more tip, before assembling the jig, give the sliding surfaces of the adjustment blocks and the back of the fence several good coats of wax. I waxed the entire jig, with the exception of the material rest ledge. I plan to put a thin strip of PSA micro-abrasive (40 micron maybe) on the ledge to prevent any unwanted movement of the work piece on the first cut before hooking it over the key.
I mounted my jig to the standard miter gauge that came with my Unisaw to use with my dado set, but you could just as easily make your own runner to fit the miter slot on your saw or router table. The plans state that you should mount your widest dado set (or router bit), position the end of the fixed material rest against the blade, and screw the fence to the miter gauge. I saw no need to ever have a box joint wider than ¾” so that is the blade I mounted to determine the location of the miter gauge mounting screws.
Does it work? Yes. I used some old dried up, splintery pine scrap to test it. Set up your dado blade, set the blade height to the thickness of your stock (plus the thickness of the material rest) on the jig. Run a cut in a piece of scrap the same thickness as your stock. Put the cut over the key and adjust the key so it just fits the test slot. Don’t make the fit too tight or it will compress the key legs and your spacing will be off. Remove the scrap and set the spacing from the blade to the key. Lock everything down. Put your first cut over the key and make another cut. I suggest you cut a complete joint in scrap to test the fit if you are going to be actually making something with the setup, but I was just playing so I simply checked the fit with a rule then made the cuts. This was the result. Not bad for my first whack!. . . Carole Valentine
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