The easiest is with a dado blade and size is pretty much immaterial. I saw a video of someone who did some crude testing with different size fingers and a press with a pressure gauge to see how much pressure it took to destroy the joint with different sizes of fingers and there was very little difference between any of them. So make them with what ever is convenient for you.

There are quite a few articles on making a jig and also quite a few videos on the same. Just google box joint jig and finger joint jig. Both terms are used for the same thing. If you think you might want to do lots of them then I recommend either the Incra I box jig or an LS positioner. Here`s a link to a magazine article showing how to make one. It may require some fine tuning after to get the spacing right. https://www.woodmagazine.com/woodworking-tips/techniques/joinery/box-joint-jig

 

my 1st choice would be to use the table saw and a shop made sled to make those box joints.....
Here's some ideas to work w/....

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I just got this video in my emails from Fine Woodworking and it may be easier to follow. https://www.finewoodworking.com/201...ource=eletter&utm_medium=eletter&utm_content=fw_eletter&cid=76047&mid=943761398
At the beginning he says you need a box joint saw blade but a dado blade is just as good. In the above mentioned strength test the person doing the test even tried one joint with eigth inch fingers which you could do with a full size flat top ripping blade but there was no strength advantage to doing that and it was more work.

The first critical part of doing this is to get the key exactly the same size as the thickness of the blade(s). That`s easy to do by cutting a groove and then work on the key until it perfectly fits the groove. The video shows how to make adjustments after doing a mock up with scrap.

 

I do lots of small finger box joints with my Incra LS Positioner. Makes it amazingly easy. Here's one with 1/8" fingers.

 

Really huge fan of my Incra LS Positioner on my table saw. I have the Wonder Fence as well for making the joints, both dovetails and box/finger.

 

You have received some great advice on making a box joint jig. There are several slight variations, but all will produce good results if you can get them adjusted just right. I strongly suggest that you get yourself a dial or digital machinist's caliper, because you will need the wood pin, the blade, and the space between the pin and the blade to be accurate withing a few thousandths of an inch. You cannot do this with a tape measure. Without one, you will likely spend all day making scrap, trying to get everything adjusted just right. The jig that @Stick486 posted is a very good one. It even has the replaceable sacrificial strip. You will need a new one of these each time you change the blade height position or change the blade. It keeps the blade from chipping out the back side of your work piece as the blade teeth exit the wood. You can use a dado blade, but the bottom of the cuts are frequently not flat using them. They sell Box joint blade sets that cut 1/4 & 3/8" box joints that are perfect, but for 1/8" box joints, I use a Freud Ripping blade that has a flat square tooth FTG grind and it makes great 1/8" box joints. You may already have a ripping blade with these square cut teeth. ATG Alternate Tooth Grind combination blades do not work very well for making box joints. I have tried about every other way to make box joints and the best and cleanest cuts have been with the table saw, the right blade, and a good jig with a sacrificial insert.

I make a lot of boxes using box joints of different sizes. If you are like me, you will end up getting the 1/8" FTG Ripping Blade and a 1/4-3/8" box joint blade set plus an Incra I-Box jig like I did, because I make a lot of box joints of different sizes and the I-Box jig is so easy to adjust, but don't spend all this money now. You can get very good box joints for this small box using a good ripping blade and a shop made jig. Tight fitting joints are achieved by building the jig accurately.

Charley

 

another plan to add to the mix...

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Thanks to all for your ideas and suggestions. The videos were also very helpful. The Incra Positioner sounds really cool, but it's out of my budget and I don't make enough of these to justify it anyway (not that that would stop me, but the Budget Committee President, aka Wife would not approve!).

It sounds like they do not make dovetail jigs this small (I didn't think so, but I thought I'd ask), so I will use one of the sleds mentioned above.

 

So guys, why wouldn't you use a finger-joint router bit?
I understand the use of the table saw, but I'm confused as to why you wouldn't use a bit in the router? Fully adjustable, repeatable..... Yes, you'd need a backing block to reduce tearout (no different to the table saw it seems), but I'm struggling to understand they "why not"?

 

So guys, why wouldn't you use a finger-joint router bit?

size limits... (height)
and it'd be a box joint bit... it's tough to make 90° turns w/ a finger-joint bit....
the bit pictured is average size..

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FJ vs BJ...

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Also known as finger joint and splice joint. You'll find more references, especially older ones, referring to a box joint as a finger joint since it appears as if you laced your fingers together. If your criteria is to name according to the application as in calling the finger joint a box joint then you should also call the one that splices lumber end to end a splice joint. Unfortunately there is no consensus as of yet. Maybe in a few years. The trend seems to be moving towards what Stick said but be cautious as the historical norm is otherwise. Other terms include tapered finger joint instead of just finger joint and splice joint.

 

Fair enough, terminology accepted (although seems to be interchangeable according to the interwebs usage of it).
Doesn't answer the question, and given the original box, still seems like a candidate to consider.

 

that happens often w/ many things...

 

But you didn't supply any answer to my question, Stick?

 

FWIW...
box on the left, finger on the right....

 

assembled 90° box joints...

 

assembled finger joint...
there is no 90°'ing this joint...
it's a board stretcher joint most commonly found in paint grade moulding where a length of moulding is made up of numerous short pieces...

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Okay, yes, I get the difference. What I'm asking is if the box joint router bit be used to create the joints required for the new box, why would you use the table saw over this method?

THAT's the question I want answered

 

Okay, yes, I get the difference. What I'm asking is if the box joint router bit be used to create the joints required for the new box, why would you use the table saw over this method?

THAT'S the question I want answered

I said yes you can but it has size limitations..
the bit is only so tall and that's the controller of the width (not thickness) of the board you want to or can use ... (the max will/can be only twice the height of the bit w/ a bit of work)

we want KISS/MISS here...

 

Gah! Sorry Chuck, I appreciate the info, really I do. But nobody seems to want to answer my actual question.
Can anyone explain why several of you are proponents of the table saw rather than a router table for this job?

 

the TS gives you a wider range of joint sizes and widths of material..
easier set up, less waste, work and breakage...
did I mention mega cheaper too...
way more cuts w/ a TS blade then ever possible w/ a router bit..
hence.. TS for production... RT for occasional shallow use....

however the router bit is a 1st choice asset if you had, say, a really wide slab of 4, 5, 6 or even 8/4...
use your bit on the end grain 1st and then resaw the slab into slats...
cutting the slab to to slat length to start is a big plus...
it'll be just like down town...

 

When making box joints with the box joint router bit shown above, your box height will be limited by the height of the bit and number of cuts that it makes. It might be possible to flip the board and repeat the cut from the opposite edge to double the board height, but the board height and bit settings will need to be very accurate, or your center box joint won't go together.

Using a straight router bit or spiral bit will let you cut one at a time and using a jig like the photo posted, you increment the board however many times is needed to cut the box joint all the way across the full width of your work piece, so the height of your box can be anything that you desire.

I prefer using my table saw to cut box joints because it's easier to make the cuts with reduced tear out of the edges of the cut, and I can make a box of any height. The table saw blade teeth only cut the joints in one direction, but the straight router bit cuts forward on one side of the bit and backward on the other side of the bit, at the same time. Avoiding tear out of the cut edges is very difficult because sacrificial edge protection is required on both sides of the work piece. The table saw only requires the sacrificial edge protection on one side of the work piece, and it can be re-used, because the blade to sacrificial strip position is the same for every cut made during that setup.

Charley

 

Excactly the reasons Charley gave. To expand on what he said a bit and to help explain why the router wants to tear grain: the widest part of the bit is through the dead center. So as the bit goes through your wood when the bit gets to its widest part at the middle the force the bit is exerting on the wood is 90* to the point of contact. On the left side of the bit that's straight towards the wood but on the right side it's 90* away from the wood so there is nothing on that right side to resist the shear forces on the grain unless you are using a sacrificial facing board. The opposite happens on the way out. The shear forces are 90* on the left side. As Charley said the force exerted by a table saw are straight back so the chances of ripping part of a finger off are reduced to close to nothing and the cut is usually cleaner.

That's why I always use a table saw for that joint and as Stick pointed out it's cheaper to use a TS than a router. The above explanation also applies to other routing jobs like rabbeting too. The closer you come to having half the bit into the wood the more likely you are to experience tearout. In physics whenever you have rotary motion the force applied is always tangent to point of contact.

 

Thanks guys, now I understand. I knew we'd get there eventually!
I now also understand better use cases for the box-joint bit, not that I'm likely to be working with larger pieces and resawing at this stage.

Hm, so I'd have to be very accurate still with my TS jig when making it though, right? That's one of those things I get more nervous about.

 

thanks guys, now i understand. I knew we'd get there eventually!
I now also understand better use cases for the box-joint bit, not that i'm likely to be working with larger pieces and resawing at this stage.

hm, so i'd have to be very accurate still with my ts jig when making it though, right? That's one of those things i get more nervous about.

what for...
Just follow the directions and don't get all worked up over it...

 

Well, let's toss in one more. I chose the ibox jig, which adjusts to the blade's total width. You can use a dado stack of any width you wish. You fit one side of the jig "feeler" to the blade, then turn a small knob until the opposite feeler just kisses the other side of the blade's teeth. This pretty much eliminates the setup hassle. You use a backer board for tearout. You could also get one of the blades that cuts either 1/4 and 3/8ths box joints with ease and you can use just about any width board you intend to use. Box joints are cut a little deeper than the thickness of the board you're using. Then you sand or saw off the slight excess. Japanese pull saw is best. Here's a pix of the jig: You can also use it on the router table.

Here's a video.

Here's one using a router table:

 

Yeah, that looks like a good way to go.

By the way, you can use a flush trim router bit to cut off the fingers that stand proud. Works really well.

 

Yes it does. I usually trim off the excess this way, but I found that double sided taping a spacer under the box side being trimmed flush, keeps the overhanging un-cut ends from holding the box up off the router table and at a slight angle. This avoids scalping the box side that you are trying to cut flush. After one side of one corner is trimmed flush, I then peel this spacer piece off and move it to another side that has un-cut pins facing down. You need to keep the box side that is facing down parallel with the router table, or flat on it for the flush trim bit to cut only the excess pin length and not scalp the box side.

I'm tired, so I hope this makes sense.

Charley

 

some other plans...

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Well I have no dado stack for my table saw, so I'd have to get a flat tooth grind blade and work it a little different, but that's ok.
It's not currently on my highest priority list, so it gives me time to investigate options. I imagine at some point I will want to make some box joints.