Help, I can’t do thin box joints

sunnybob said:

You are routing along the edge of the grain. Thats wrong 99 times out of a 100 (Maybe even more).
Box joints are for end grain, especially if you are using a router.
Jointing a long edge would usually be with glue or splines.
Tell us what you want to build for more detailed help.

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I can't improve on the above member's advice.

I agree with the others. Box joints should be cut in end grain, not long grain.

Also, using a router just never did a great job at box joints for me. I found that I could do much better at box joints on my table saw, mostly because it cuts in only one direction, where a rotating router bit cuts in two directions at once. Keeping the tear-out to a minimum in most wood requires a sacrificial board to act like a zero clearance insert, holding the wood fibers adjacent to the cut so they don't break free as the blade exits the wood. With a router bit, you need sacrificial zero clearance inserts on both sides of the work, since the spinning router bit can cause tear-out on both sides.

Cutting the box joint on a table saw only requires a sacrificial strip on the blade exit side of the wood, so it is easier to manage. Using a saw blade or blade set that has an FTG (Flat Tooth Grind) will produce very clean box joint cuts with parallel sides and a smooth flat bottom of the cut. For 1/8" box joints I use a Freud LM72R010 Ripping Blade. The tooth width is actually 0.126" so very close to 1/8". For 1/4 and 3/8" box joints I use a Freud SBOX8 blade set, which is actually two saw blades with offset FTG ground teeth. With the printed sides facing away from each other, the blades cut 1/4" box joints. With the printed sides of the blades facing toward each other, they cut 3/8" box joints. The offset teeth of one blade fit into the gullets of the mating blade when cutting 1/4" box joints.

I was once told "you can't cut box joints in plywood", but I now do it frequently. I make quite a few boxes, usually in Baltic Birch plywood, and use the FTG blades noted above with perfect results. I now use an Incra I-Box jig, because it is so easy to calibrate and adjust for different widths of box joints between 1/8 and 1" widths. I had about a dozen shop made box joint jigs and they all went into the burn pile when I bought the I-Box jig. It comes with a sacrificial strip that I move to a previously uncut position just before I begin making box joints. It is made from 1/4" MDF and I copied the original and made about a dozen from one 2' X 4' piece of 1/4" MDF, so I would have spares to last me a very long time.

Attached are a few samples of my box joints in Baltic Birch plywood.

Charley

I don't like using the router for box joints. Instead, I popped for the Ibox jig and the two blade set mentioned by CharleyL. If you want to do box joints on the long grain, you could probably do it with the Ibox, but I'd make sure you used a sacrificial piece behind the workpiece.

I love the Ibox jig (below) because it can work with any blade width you set up in a dado set. But for end grain boxes, the Freud double blade set will cut 1/4 to 3/8 th is a pleasure. The jig has a simple adjustment you can dial to any blade width.

I can see doing the pins and sockets on the long grain edge if you were making a tall box. If using ply, I'd go with Baltic Birch or Apple Ply. Its a nice way to make drawers

BTW, welcome to the party.
Pictures. Incra Ibox jig on table saw. Freud SBOX8 blade set. Diagram of box joint (pins and sockets)

For beginners or very occasional use the first two shots show the first box joint jig that I made, very simple and it worked well. Some time later I won a jig made by an associate company of router forums as a contest prize. One like it is simple to make out of wood at virtually no cost, as was the first one of mine.

I went with my I-Box jig, mostly because it is so easy to adjust for different blade widths. Because I was making box joints of different widths and board thicknesses, I had a dozen or more shop made box joint jigs. Some worked very well and some were just OK, but they all worked and were all for different sizes of box joints, either different widths, or different pin lengths. If you are using your jig as the zero clearance insert and you want to cut box joints in thinner boards than was last cut on the jig, you need to either make another jig or come up with a modification to your jig that provides a sacrificial piece behind your work to minimize tear-out. But having so many box joint jigs hanging, or stacked up in the corner of a very small shop posed significant trouble for me. I was running out of space to keep all of them. So getting my I-Box jig saved me considerable shop storage space.

When I saw the demonstration of the prototype for the I-Box jig by it's inventor at one of our club's events, I knew that I had to have one, but I had to wait about 3 months before they became available. I can't say that I got the first one, but I certainly got one of the first production batches. It has lived up to all of my expectations. I own a Leigh D4R dovetail jig, and it's very nice to have for cutting dovetails, but since getting the I-Box jig, I think I have only cut dovetails once. Everything needing a strong corner joint is now being made with the I-Box jig, because it's so easy to set up and use. If cutting the same size box joints as I had cut the last time that the jig was used, I just put it on the saw, set the blade height desired, and make one quick test cut to be certain that nothing has changed, Then I position the sacrificial strip to an un-cut area and begin cutting my box joints. I can do this in less than 5 minutes.

You can use the sacrificial strip to cut about 15 different times before you need to invert it and begin using the top edge for about another 15 joint settings. So about 30 new box joint project setups per sacrificial strip. When I received my I-Box jig I knew that I was going to need more of these strips, so I bought a 2' X 4' piece of 1/4" MDF and proceeded to make copies of the sacrificial strip that came with the jig. I used the table saw to cut out as many strips as I could get out of that 2 X 4' piece of MDF. Then I set up my drill press to drill one of the holes using edge and end stops so I could drill the same hole in the same position of every sacrificial strip. When drilling these holes, if you set the drill press stops correctly, you can drill the first hole, then flip the strip over and drill the second hole, then flip the strip end for end and repeat to drill the remaining 2 holes the same way. Then I removed the stops from the drill press table and installed a countersink bit, and proceeded to countersink all of the holes from the smoother side of the sacrificial strips. I think I made about 15 sacrificial strips in about an hour of easy shop time. Incra is selling these at about $10 plus shipping for 3 of them. I paid less than $5 for the MDF and spent a fun hour in the shop to make $50 worth of sacrificial strips. I may not live long enough to need to make any more of them. It will certainly take me years to use them up. I'm only on my third one now.

Charley