How to Make a Box Joint Box





Introduction: How to Make a Box Joint Box

Anyone that reads my profile may notice that woodworking is first on my list of interests. So where are all the woodworking articles? Fact is I don't often document those projects. Making box joints is something I have done so much I have had a chance to photograph the process.

If you're really going to do this then read the entire set of instructions before you begin because some things are revealed later that you should be aware of earlier. This is done for reasons of brevity and conciseness. This is already long enough! Maybe that is why this technique seems tricky. Once you know it all it is actually pretty simple and easy.

I'm pretty sure with my instructions anyone can do this, but if you've any questions well, leave a comment, and I'll try to elaborate on anything you are unsure of.

Step 1: Do a Jig

I don't mean any Dancing With the Stars sort of thing. No, to make box joints a fixture jig is used.

Hopefully the graphics here will explain all but if not this is how I make mine.

First I take a piece of wood and screw it to my miter gauge for my table saw. Make sure the wood is flat flush with the table.

Now determine the width of finger joints desired, set a dado blade accordingly. Put blade into the saw, set height etc.

Run the miter gauge with the piece of wood screwed to it over the blade making a notch.

Remove wood from miter gauge and carefully measure the notch.

Step off the measurement of the notch and cut an identical notch into the wood piece.

Make a square pin piece that fits right into your new notch and affix it into there using glue, maybe a nail or something too.

Reattach your completed jig back onto your miter gauge exactly where you took it off. If you need to make a pencil mark to get it right back where it was whatever it takes. It is vitally important that your jig is in the exact right spot on your miter gauge though.

The accuracy which you construct your jig will transfer to the box joints you will make with it so do a good job. I measure my notch with calipers accurate to .001 of an inch. I'm not really too sure if anything else would work. But you're more than welcome to try. I undersize the stuck out part of my pin a little to make it a bit easier to get the box parts on and off it. I just sand the pin a little after it is put together.

The astute observer will notice that the jig is a pattern of one box joint that we will simply repeat over and over in order to cut the successive joinery.

Step 2: Cut Sides

This sounds simpler than it actually turns out to be. This is where some experience will eventually pay off as you perform this task more. You see this joint chews into your wood stock somewhat. In that I mean with a simple butt joint in wood your side is your side, but this joinery uses up some of that stock material in it's nesting nature. What is more is in order to really make this joint well you should overhang the fingers a little. Then once the box is fully done sand the  fingers that stick out flush to the sides.

What I am driving at here is your completed box will have sides smaller than your cut sides are. How much smaller depends on the thickness of the wood, and the amount of overhang you allow for with your joint fingers. Initially this shouldn't be all that critical I mean just be happy you're making boxes, but down the road when you set yourself to some more demanding tasks it is something you'll have to work on.

For now focus on making two pairs of equal length sides for your boxes. Oh yes, your sides have to be square cut as well.

Step 3: Perform Test Cuts

Every time I do this I always do test cuts on the stock I plan on making boxes out of. The kind of wood it is, the various adjustments, dado width, and blade height, all have to be dialed in to work with each other. Joints should fit together without being too loose, or too tight.

But if we're going to be doing test cuts I guess I have to tell you how this whole cutting box joints thing works now don't I? This is the abbreviated version, the full version will come later when we're making our actual boxes.

Take your two scrap pieces and set them standing up on your bench like they are the corner of a box.

Put an X or some other sort of a mark on the top edge of each piece where they come together.

Take one and butt it up against the side of the pin on the jig. Run a notch into it. (red in the graphics)

OK now this is the tricky part so pay attention:

Take that first piece (red) you just cut and put the notch in it, flip it over and put it's notch onto the pin. The one tooth should fill the gap between the pin and the notch on the jig. Now take your other piece (blue) and butt it to the edge of the first piece mark to mark. You should notice that if you pass the work over the saw blade your second piece (blue) is going to get it's corner notched out. If that is how it looks to you go ahead and do it, make the cut.

Now you're going to gang cut the two pieces together. Take the first piece flip it back around and put it's notch over the pin of the jig. Put the cut notch of the second piece onto the pin. Make a new notch through both pieces, then put that new notch onto the pin, notch, move, notch, move until you've gone the length of the pieces.

Now line up your marks again and put the pieces together. Don't tell me you marked the second piece where the saw cut the mark off. ha ha I do it all the time! We'll learn to back that mark off someday.

This is harder to explain in text than in pictures, so try to follow along with the amazing graphics I drew. Because it really isn't as hard as it sounds.

Step 4: Lay Out Sides

Now hopefully you can still count to 10 without having to take your socks off, and you've dialed in your cutting setup too. If I am making a box out of one piece of wood I like to have my sides all in order so I line them all up so the grain wraps around the box. It is an extra little detail I just like to do it isn't important though.

What is important is that you lay out your sides so they do wrap up into a box.

Step 5: Box of Cards

Some arrange their pieces in a flat cross like pattern I like to prop mine up. Propping them up helps me keep it all straight while I number all of the corners. I number my corners 1 to 4 and put the number onto each piece. Doing this will be important later on.

My numbers are a little hard to see in the image but they're all there.

Step 6: Cut Notches

Stay with me on this step. We're only going to cut one notch into each board right now. But there is one other thing you have to think about with this step. You have to keep your parallel box sides identical to each other. By this I mean if you have a notched corner on one, you have to have notched corners on  the opposite side too. I'll draw another picture to explain what I mean.

The sides in the graphic that are the same color have to match. So you're either cutting them all first, or second. Remember butt number up to number in this step while notching. It is just like butting up mark to mark while test cutting.

Step 7: Gang Up

If you got this far you are virtually done. All you need to do at this point is set your notched sides onto the pin and have at it! If your initial notches you made are right then this has to come out right as well. So just cutting down the line twice and you'll have all of your box joints done for a box.

I would just like to add that I clamp my sides together and this gets me more precise cuts. Saves me some effort in that I don't have to grip all the pieces together too. It'll work if you don't clamp all your sides together while you gang cut them, just not as good and it'll be tougher on you to do too.

Step 8: Stacked

As I cut my boxes I like to keep them dry fitted together so I keep all the sets together. I'll leave it to you how you'll handle putting bottoms onto your boxes, tops, etc. I usually just cut a piece to fit and glue it in there myself.

One more thing, I've cut about a billion of these by now and over time I've concluded that you only really need to make two sizes 1/4" for thin walled boxes, and 1/2" for thicker walled ones. I've seen fancy adjustable jigs for making box joints but making one of those is kind of silly to me. Just adds to potential errors and general confusion as far as I'm concerned.

But that is just my opinion you're free to do as you choose.



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    See also:

    CMT 230.224.01 Blade for Box and Finger Joint Set with 8-Inch Diameter by 24 Teeth FTG Grind and 5/8-Inch Bore

    Oshlun SBJ-0830 8-Inch Box and Finger Joint Set

    Forrest 8" 2-pc Box Joint Blade Set

    If you plan ahead a bit, you can cut a groove in your side sides (along the 'bottom' edge) to accept a board cut to fit into that groove to serves as the box bottom.

    Cut square, it helps fit the box together as well.

    Of course, you can do the same thing for the box 'top,' then cut along the sides of the finished box to create a lid that can be hinged as shown in the finished product here.

    Buy cutting a groove* along the inside of your sides, then, after assembly, cutting a matching groove along the outside of your box, you can create a box such that the top and bottom sections have a 'lip' such that they fit together and register one to the other.

    These grooves need to be cut to a dept equal to one-half the thickness of the stock such that the depth of each of the grooves is equal to half the thickness of the stock/side.


    Good job with the illustrations. Here are some thoughts that came to mind as I read the first few steps.

    Determine what the finished inside/interior measurements are/need to be: Length, Width, Height.

    Add these to your sketch.

    Then, select your stock - the wood you will use to build the box and measure it's thickness.

    The thickness of your stock (the board(s) used to make each side, top and bottom (six (6) pieces will be needed to determine the outside measurements of your box and the depth of the cuts made to form the tongues and sockets of your joints.

    That is, if the stock is one-inch thick, you will cut each side piece two-inches longer* than the inside measurement on your sketch and the depth of the cuts made to form the tongues and sockets will bee (at least) one (1") inch.

    * Most folks who make these joints add a bit (1/32" - 1/16") to these measurements such that the toungues actually extend betond the determined/desired exterior dimensions. After final assembly and glue-up, they are trimmed and sanded flush with the respective side.

    So, with the intent of crafting a square box with interior dimensions of 5" x 5" x 5" using stock (wood) that is one-half (1/2") thick, you will need to cut four side pieces to a length of 5" + 1" + 1/16" or 6-1/16" long.

    If we are going for a Cube, the side pieces will need to be six-inches wide to accommodate a top and bottom for the finished box.

    For the purposes of these instructions, and the focus upon making the box-jointed box let's assume we are making a Shadow Box that will have neither top nor bottom.

    With that simplification in mind, the width of your stock is immaterial and the steps necessary to add a bottom and top (which would need to be done prior to cutting the box joints) can be eliminated.

    So, cut four lengths of stock to 6-1/16"

    Pay attention to the grain pattern and 'good' or 'best' face of your stock to determine which face will serve as the interior and which the exterior of your finished box.

    If you have enough stock to do so, (25 or more inches in length) cut all these pieces from one board and mark each section (with an 'A,' 'B,' 'C,' & 'D,' respectively) on the 'best' side and with a number (1, 2, 3, & 4) on either side of your cut lines to represent the 'ends' that will come together to form each corner of the finished box.

    Mark up your stock this way BEFORE Cutting to help you keep the 'best' side in mind when cutting the box joints as well as which end 'goes with which.

    Then take another length of the same stock and mark (as above), then cut a series of test pieces which need not be as long as the side pieces of the box you first cut but long enough to hold safely as you mak your test cuts in thier ends.

    Ideally, the width of the tongues (and, thus the sockets) should be determined such that they added up to the width of your stock. Thus if your stock is three inches wide, an even number of tongues and sockets will be had if the width of the tongues and sockets is 1/8", 1/4", 1/2" or even one-inch.

    For about eighty-three dollars (US) you can buy a Freud Box Joint Cutter Set, Cuts 1/4 In. and 3/8 In. Joints (SBOX8) that will simplify cutting 1/4" or 3/8" tongues and sockets, or use a router MLCS Woodworking Box Joint Router Bit - 1/2" Shank to cut joints in stock up to 1/2" thick and <2" wide.

    Otherwise, using a stacked Dado Blade set, put the blades and cutters together to achieve the desired width of cut - and cut a series of tests pieces before cutting into your 'good' stock!

    Nice job with the Instructable.

    One thing that is worth mentioning is the use of saw blades that are particularly suited for making box joints. They cut flat for a better fit rather than the angular cuts that a typical dado blade set makes.

    Maybe you can help me out

    I made a pfred2 1/4 inch jig for my router to the exact measurements.

    The issue I am having is the joints are little too tight.

    Is there some type of adjustment I can make to the jig in order to make the joints a little looser?


    I think I figured out why the joints are so tight.

    I have to make smaller tails, to do that the jigs pin has to be a little closer to the notch.

    So if the test board comes out too tight like mine did move the jig pin closer to the notch

    If the test board comes out too loose then move the jig pin away from the notch.

    I hope this helps anyone else


    One of the downsides to the non adjustable jig is you do have to make it very accurately for it to work properly. I use machinists calipers when I make them. Though making a long pin, and cutting it and using the cut off as a gauge block would work too. For this jig to work it has to be very close to perfect. That accuracy is what you repeat using it. So it is sort of the secret of the whole process. Do it right once, and then you can easily do it right a thousand times too. Then you need to cut the notches the exact right size too. Whenever I did this with an adjustable dado blade I'd spend some time making test cuts, just to get a good fit. I would make my pins a little undersized too. Because if it is really tight it is hard to index the work on the pin. What I do is sand the pin by hand a little after the jig is together, just for a little clearance.

    The up side to the non-adjustable jig is when it is correct then there is no adjustment to get out of adjustment. Every time you use it you get the same results.

    Also, one can make the jig adjustable, so that the front can
    be moved from side to side to change the size of the pins. Using a 10X32 screw
    as an adjustment tool, one can get 1/128th of an inch per quarter turn
    and that way dial the jig in post construction without messing with the pin and such.
    Here is a picture of mine on a little (dirty) router table for ¼ cuts. The face can be
    replaced to match other sizes.


    Couldn't I use a router instead of a table saw? I cannot use a dado blade with my cheapo table saw.

    So I make the jig with my router miter gauge the same as you did with the table saw miter and then cut the box joints with the appropriate router bit.

    Do you see any issues using a router with your terrific box joint jig set up?

    Thanks so much for sharing this.

    I have seen this done with a router myself. The biggest problem is router bits cannot remove the volume of wood that dado blades can. Size matters. So stacking the pieces together might be too much to ask a router to do. I've made box joints both ways, cutting each side individually, and stacking. Stacking offers advantages over individual cuts. Besides the obvious reduction in repetition stacking causes the cuts to be more uniform too. The fingers just line up better when cut stacked, then assembled.

    So what I'm saying is it will work, but not quite as good.