Well, folks, I can no longer criticize both ShopNotes and/or Woodsmith for publishing an inferior method for cutting box joints on the table saw. Finally, after 10 years or more, ShopNotes #75 shows how to cut box joints using the stacked cutting method, where most of the cuts are made through both boards at the same time.
In the past, they cut the mating pieces separately, and that's often an invitation to disaster, especially with wide boards. Pages 12 through 14 of this current issue illustrate the technique. Now I can safely eliminate about 75 e-mail messages from my Sent Items list.
Edwin Hackleman's Box Joint Jig and correct Procedure to use it.
The Table Saw (TS), a stacked dado set, and my shop-made jig are all you need. Box making is lots of fun, once you get the hang of it. But, it takes practice. Skilled boxmakers are rare birds.
The "magic" key used on a box joint miter gauge fence is the same width as the tenons (pins) and is glued to the bottom of a fence inside a slot. When cutting, it is positioned with its left side to the right of the blade at a distance that is just a hair less that its width. That will form a tenon that just fits snug into a mortise (notch). The dado set cuts a mortise that is exactly the same width as the key and leaves behind a tenon as you move along.
I have made four of these box joint fences for the miter gauge, with keys at single-blade width, 1/4", 3/8", and 1/2". That's all you will probably ever need because you can join big 8/4 stock with 1/2" tenons. I suggest you start by making a 1/4" or 3/8" modular fence, structuring the key width around your stacked dado set. Join ordinary 3/4 or 4/4 for starters. Or use some plywood. I have successfully joined plywood with box joints, although the "books" say this is a no-no.
My fences are all about 4" high and 18" wide, made out of 4/4 hardwood stock. I also glued a 3" wide piece of 1/4" hardboard to the bottom of the fence for the stock to ride on. The key is cut the same length as the width of this foot. You can either bolt the fence to the miter gauge with holes for the bolts that allow lateral adjustment, or make your own fence carriage. I made my own carriage that uses two hardwood runners, one for each slot.
Set the jig by adjusting the blade height and the key location relative to the blade using scrapwood, setting it first by eye as close as you can. Start with scrapwood that is similar to your workpieces.
My "foolproof" cutting method (now shown in ShopNotes) is as follows:
1) Cut the first pass with the first board pressed against the key.
2) Turn the board 180 degrees and straddle the key with the new mortise.
3) Press the second board against it and make a pass to cut an outside notch in it.
Here is where I jump ship from the old Woodsmith/ShopNotes "published" method.
4) Unstraddle the first board. Press the second board against the key.
5) Turn the first board 180 degrees again, and straddle the key with it pressed flat against the second board. Clamp them together if they are large boards.
6) Cut BOTH boards at once with this pass and all remaining passes.
7) Before moving onto the next pair, check the cuts to be sure you got full depth all the way across. If you notice that one or two are shallow, it's because the board slipped up during the cut. Recut it now.
You will now have a perfect fit, provided your jig was set correctly to begin with. I always make a trial cut and fine-tune the adjustment with a couple of scraps. The scrap can be narrower than the true stock, but it should be the same thickness to set the blade height. Cutting the scraps is like a pitcher warming up at the mound.
If the boards are big, I sometimes use the scrap in step 3. The reason this 7-step method works is that all the cut tenons and mortises that join are right next to each other. They share the same error if it exists, and no error compounds from one cut to the next.
a) If the tenons are too thin, move the key away from the fence; if the tenons are two thick, move the key closer to the fence.
b) If the tenons are too long, drop the blade; if too short, raise the blade. I leave my tenons just a hair proud and sand them smooth after assembly. Edwin has been known to cut four pairs of scrap until he gets an acceptable fit.
1) Lay out the box on the bench and label your eight workpiece ends 1&1, 2&2, 3&3, and 4&4 before you start, about an inch or two from the end. These must pair up before and after you are done. Except for step 3 above, you will always be able to see that letter on each board on the lower right just before you make a cut. In step 3, they kiss each other.
2) Use a pressed wood (1/4" masonite) backer board the same width as the fence height and 16" long pressed against the jig carriage. Believe me, you will get tear out. This fights it.
3) Yellow glue is impossible to beat when it comes time to assemble. Use a thin strip of 4/4 scrapwood to help spread the glue down inside the cuts. These strips are really handy. Save a few.
p.s. Print these instructions and take them with you to the shop. These may be the best I have ever written on this procedure. Some things get better with age.
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