Making Box Joints

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About: Retired Electronic Design Engineer. Member of The MakerBarn.

There are several Instructables showing how to build Box Joint Jigs, but not much on how to actually use the jigs. This is an Instructable on how to use the jig to best advantage.

Step 1: Prepare Your Material

Cut the sides of the box 1/32 to 1/16" longer than necessary. Make sure your stock is flat and square. It is also important that the width of all sides is identical. Also make sure opposing sides are identical in length.

Mark the material to show which edge will be the reference edge on each piece. Draw an arrow on each piece to show which edge the cutting will start on. When cutting, the arrow will always point to your right.

Step 2: Setup Your Dado Blade

Setup the Dado blade to match the size of the box joint jig you plan to use. We will be using a 3/8" box joint for this project. For additional information on setting up Dado blades, see the Instructable "Setting-up a Stacked Dado Blade".

Step 3: Making a Backer to Prevent Tearout

There are two things that greatly improve the Box Joint Jig, the Backer, and the Spacer Block

One is a backer, made of thin plywood. In this case a strip of 1/4" plywood, 2-1/2 wide was used. A 3/8" wide notch was cut (sorry for the blurry photo) to clear the index block on the jig. Two pieces of double sided tape are used to hold the backer to the jig. The backer greatly reduces the chance of tearout on your workpieces.

Step 4: The Spacer Block

One pair of sides butts directly against the index block of the jig for the first cut. The other set must start exactly 3/8" (for a 3/8" joint) off the block. The easiest way to do this is to make a spacer block. It this case a small block of 1/2" MDF was used. The block must be a true rectangle with square corners because it is going to be used as a reference tool. Using the jig, cut a slot high enough to clear the height of the index block on the jig, similar to the Backer. Make sure you have the block firmly against the index block when making the cut. Set the Spacer Block aside for use with the second set of sides.

Step 5: Set the Cutting Height

Set the blade just slightly above the thickness of your workpieces. When the box is glued-up, the fingers should protrude slightly so they can be sanded off flush with the sides.

Step 6: Beginning the Cuts

The front and back will be cut in the same manner. The left and right sides will also be cut in the same way, but different from the front and back. So grab one set either front and back, or left and right, and set the other set out of harm's way.

Start the cut with the piece firmly against the index block, with the arrow pointing to the index block side.

Make the cut, then advance the piece to the next position, cut, and so on until the end is complete.

Step 7: Flip the Piece and Do the Other End

Flip the piece over. Make sure the arrow is pointing toward the index block, then cut the second end the same as the first. Do both pieces in the set the same way. Make sure to pay attention to the arrow and always keep it pointed to your right (for this type of jig).

Step 8: The Second Set of Sides

The notches cut in the second set of sides must be precisely offset from the first set. This is where the spacer block comes in.

Place the spacer block over the index block. This should place the edge of the spacer block in line with the left side of the dado cut.

Cut the second set of sides in a similar manner as you did the first set, but start the cuts with the spacer block in place. After the first cut, remove the spacer block and use the index block to setup each cut. Do one end, flip the piece over and do the other end. Be sure to keep the arrow pointed to your right.

Step 9: The Results

This is what it should look like. The joints are snug, but enough room for glue, and the edges of all sides line up without steps.

Box joints are an easy way to make strong attractive joints quickly and easily. I use them in a lot of projects, I'm sure you will as well.

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    31 Discussions

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    tim_n

    1 year ago

    Sadly dado blades are banned in the EU. Nice pictures though

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    sgt_carbonero

    1 year ago

    In order to make different widths of cut, what is the optimum distance from the blade for the Index block? I assume the index block is stationary.

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    sgt_carbonero

    1 year ago

    I assume the rails float slightly and the unit rests on the base entirely?

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    DocHowells

    1 year ago

    For UK users, I imported set of stacked dado heads and appropriate arbour from US and re-engineered my "Cheap" UK table saw, which was out of warranty anyway. As hobbyists there is always an element of risk in all that we do. As Wing Commander Douglas Badder RAF once said: " Rules were made for the guidance of wise men and to be obeyed by fools!". WWII Royal Air Force Fighter pilot who lost both legs in accidents and continued to fly until captured by German forces, who removed his artificial legs to stop him escaping their POW camps. A real pain the the German's arse as well as the RAF. Can't keep a good man down. Where there is a will there is always a way.

    1 reply
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    geotekDocHowells

    Reply 1 year ago

    Table saw arbors are usually very simple devices. Many do have a square thread for the blade mount, which is tricky to machine. There are many very skilled Model Engineers in the UK that could make new arbors for their woodworking brothers.

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    johnLAZER

    1 year ago

    I would love to make on of your finger joint jigs, BUT, we unlucky souls in the U.K. are not able to get hold of dado stacks. For some reason they are not permitted.

    I do love the projects on the website and have gotten many damn good ideas from it.

    10 replies
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    SirCooksalotjohnLAZER

    Reply 1 year ago

    Here's a crafty dude with no dado as well: https://www.instructables.com/id/My-Super-Simple-Single-Blade-Box-Finger-Joint-Jig/

    Problem solved! Booyah

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    FlorinJjohnLAZER

    Reply 1 year ago

    You can make finger joints using a regular blade too. You only have to make more passes for one slot. You just need a mechanism or something to precisely control advance in relation to your blade's thickness. I've seen two variants so far: one using a screw with a known step size and another one using cogwheels. The simplest one, which I partially replicated, using a screw, is on the darbin orwar channel on youtube. It should be probably easily guessable: the one using cogwheels is also exemplified on youtube on Matthias Wandel's channel.

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    geotekFlorinJ

    Reply 1 year ago

    That brings up a good point. I have a jig I made for cutting box joints with a normal combination blade. I typically use a Freud LU-84, which has a 1/8" kerf. So I made a jig for cutting 1/8" box joints. It works well and is the best choice fro thinner material. This would work for those in the EU.

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    FlorinJgeotek

    Reply 1 year ago

    :-) I have a (self-made) jig that can cut any finger/gap width that's a multiple of 2 mm - that's the step length of the threaded rod I have used (about 1/12"), and also very close to the kerf of the blade I use - the blade is 0.1 mm wider, just enough for 6-8 mm fingers to fit tightly but not too tight into the gaps . For example, for 8 mm(~ 1/3") fingers/gaps, you'd cut every step for four steps/turns of the threaded rod, then skip four turns, and repeat.

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    Big Daddy FredFlorinJ

    Reply 1 year ago

    You can use a similar jig to make finger joints on a router table. Only instead of making a dado blade kerf slot, make it with the appropriately sized router bit. I recommend using a spiral up-cut bit for clean cuts that draw the material away from the cut. Rockler makes a very affordable jig for router table box joints. Hope this helps.

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    geotekjohnLAZER

    Reply 1 year ago

    I talked with others about this restriction. It seems that it originated with the mandate the all spindles and arbors stop within a specific time. The fear was that a heavy dado stack would come loose if the arbor stopped too quickly. Some rules are made without the benefit of actual experience, I think this may be one. I made thins Instructable at The MakerBarn, which is a non-profit makerspace near Houston, Texas. In my own shop I usually cut boxjoints with the Freud box joint set, which is two blades that are swapped for 1/4 and 3/8" joints. A very clever design. Ironically they are made in Italy, an EU country, as is may Freud dado set.

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    ChrisOKrazyjohnLAZER

    Reply 1 year ago

    That's very strange. You have any idea why there are not permitted in the U.K.? Just curious

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    BobH160ChrisOKrazy

    Reply 1 year ago

    Because the H&S and EU think we are mindless morons who couldn't put a screw in without instructions and a two day training course.

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    BobH160johnLAZER

    Reply 1 year ago

    I checked it out. We cannot get them here as the H&S (as usual) would not give it a CE/Kitemark unless it had the short shaft which is too short for a dado blade stack. I suppose if you were engineering savvy you could make an extension but for real safety, I would ensure it is supported at both ends to give better balance, I would hate to think of two blades whizzing around your workshop.

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    BobH160BobH160

    Reply 1 year ago

    This was on a forum and it explains it well.
    The use of universal moulder heads, wobble saws and dado heads is forbidden on all woodworking machinery (table saw, router, shaper) used with hand feed. This is mandatory EU occupational safety regulation. So the newer table saws are manufactured with purposely short arbors.

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    sgt_carbonero

    1 year ago

    How far away to put the index block from the blade? i assume you dont want it to look much thicker or thinner than the other fingers. How to do this when you may be making 3/8 or 1/4 kerfs?

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    geoteksgt_carbonero

    Reply 1 year ago

    With this type of jig, the fingers and the slots must be identical widths. So for 3/8" wide cut, the fingers must also be 3/8". In practice, the fingers are made a tiny bit less than 3/8" to allow for glue and easy assembly.

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    sgt_carbonero

    1 year ago

    To add to my previous question, how to calculate the height of the piece so the fingers dont look awkward? (that is, at the end it has a nice space, not cutting a half finger)

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    geoteksgt_carbonero

    Reply 1 year ago

    If the width of the piece is a multiple of the width of cut, all fingers will be even. If the width of the piece in an evem multiple, the fingers will apear centered.