Easy Box Joints (Adjustable Tooth Widths)

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Introduction: Easy Box Joints (Adjustable Tooth Widths)

About: If a tree falls in the woods...make things!

Box joints jigs are one of those types of jigs that have been circling the internet for years. I've seen large box joint jigs with extremely complicated plans (I even purchased and made that one!) as well as thin blade kerf jigs that everyone seems to think they've invented. There are so many different types of box joint jigs, how do you choose the one that will always work and doesn't take up a lot of space?

I'm going to show you my approach to these strong, durable, beautiful joints and we're only going to use 2 power tools. One, of course, will be your table saw. The other? A drill. And the cost of this jig? We're going to keep it below $20. Yes, $20*!

If that isn't enough to get your undershorts in a knot, I'm also going to promise that even the basic of woodworkers that have those two power tools and some basic other woodworking things (and $20) can put this jig together. I can also promise that you will feel like a million bucks after you make your first box and show it off to the world!

*Of course, I don't know where you reside, but here in the midwest, I created this simple jig for less than $20.

Step 1: Gather Materials / Tools Needed and Used

Material List

  • 3/8"-16x24" Threaded rod
  • (3) 3/8"-16 Nuts
  • (5) 3/8" (it needs to fit on the threaded rod) Washers
  • 3/8" Brad t-nut
  • 3/8" Pronged t-nut
  • 1/4"x4" Carriage bolt
  • (2) 1/4" Nuts
  • (2) 1/4" Washers
  • If you're using a miter gauge instead of a sled
  • a. (2) *1/4"x2 1/2" Bolts
  • b. (2) *1/4" (needs to fit on the 1/4" bolts) washers
  • c. (2) *1/4" Wing Nuts (or knurled thumbscrews)

  • 2x6x24" Construction grade lumber
  • 1x4x20" Pine board
  • Wood glue
  • Epoxy
  • Sandpaper
  • Masking tape

Tools Needed and Used

  • Table saw
  • Drill
  • 1/4", 1/8" Drill bit
  • 3/8", 1/2" Forstner bit
  • 5/8" Forstner bit (not really needed, but only if using a miter gauge)
  • Ruler / Tape measure
  • If using your own sled: (2) Bar clamps
  • The Advanced version uses a Bandsaw (absolutely not necessary for the main build)

*(Or whatever will fit inside your miter gauge holes)

Step 2: Figuring Out Our Jig Size

First and foremost, let's decide how you're going to use this jig. Will you use the jig with a miter gauge or with a table saw sled? If you're going to use a miter gauge, the 2x6x24" will be just fine. If we're going to use a table saw sled that you've already built, we'll want to make it the length of the front fence. And since it's going to clamp on to the front fence, we'll want it to be exactly the same size so that the clamps will...obviously fit on either side and...clamp.

How it will be connected.

Step 3: Making a Dado

Now we'll make a dado that your box joint mechanism will be housed in. This dado will be 1" squared. As mentioned, we'll be using a 6 1/2" wide piece of construction lumber. We'll need to set our blade 1" high off the table as well as 2 and 1/2" away from the table saw fence.

We'll make our first cut and then move the table saw fence about a 1/16" closer to the blade. We'll run the 2x6 through again, and move the blade closer, repeating the process until we've cut out a 1" gap in our construction lumber.

I've left an image in this step that'll show the dimensions after we are done cutting, and a link below to show me doing this step. Twofer!@!

Dado makin'.

Step 4: Cutting the Kerf, Optionally Attaching to a Miter Gauge

If using a sled:

In this step we'll make the kerf for our jig. This kerf is what we'll use to align our jig to our sled before we make those beautiful box joints. And it's a pretty simple step.

We'll put our newly cut 2x6 with the 3" lower half pointed down against our fence and clamp both sides with bar clamps. Raise the blade about an inch from the top of the sled and run it through the blade.

If using a miter gauge:

If you haven't made a sled yet for your table saw, this part of this step is just for you. I will assume you have a miter gauge, as they come with every table saw I've ever seen. You also won't need to use clamps, but will need to use a couple 1/4"* bolts and a couple 1/4" wing nuts*, or knurled thumbscrews (which I'll be using). The length of your bolts will need to be determined by you as you measure the thickness of the board you're using and your miter gauge. Since my plans call for a 2x6, and the kiln dried specs of a 2x6 are actually 1 1/2" x 5 1/2", and the metal fence on a normal miter gauge is no more than an 1/8", adding a thumbscrew or wing nut should leave you needing (2) 2 1/2" bolt.

First you'll want to line up your board so that your left edge is at least 13” from the center of the blade. I used a sharpie marker to color the tips of my bolt, before pressing the bolt in and marking my board, like a stamp. Once it's done, you can see the outline of the bolt on the wood. If not, you might have to do it a few times. Use a brad point bit the size of your bolt and mark where just the point protrudes, using tape on the drill bit as a depth gauge. Drill down to the tape and flip the board over. You should see, on the opposite side, just a small point from your brad bit. To finish it off, use a forstner bit the size of your bolt head. Since this instructable calls for a 1/2" forstner bit, and most heads on a carriage bolt are 5/8" in diameter, you can tap the carriage bolt in if you want to.

Insert (2) 2 1/2" bolts*, add 1/4" washers* and use (2) 1/4" wing nuts* or a thumb screws*.

*Or whatever size fits in your miter gauge.

Connecting to a miter gauge.

Step 5: Cutting Stop Blocks and the Pin

On either side of the threaded rod that strings through the center of the dado we cut, we'll need to create blocks that keep the rod stabilized, allowing only the center pin that we align our wood to movement. Since the pin is the only movement we want as we crank our handle, we'll want everything else to stay exactly where it should.

The first thing we'll do is cut our 1x4x20" board so that it fits nice and tight in the dado we created. If you're following along, we cut a 1" square channel in our 2x6 and will cut our 1x4 to 1" on the table saw.

After we've accomplished this we'll place the end of our newly cut board in the channel and draw a line across the edge. Next we'll use a straight edge to draw an 'X' with all 4 corners. Before cutting that section of wood and making a square, we'll pull out our drill and chuck a 3/8" Forstner bit in and center it on the 'X'. Drilling with a drill press is easy. You put the stock on the table and press the bit into the wood. Doing the same with a drill is obviously more difficult. To accomplish this a bit more easily, watch the edges of the Forstner bit as it cuts downward. Note the top of the bit and the top of the block of wood and make adjustments if you feel like it's not straight. I could have suggested using a drill bit here instead, but a Forstner bit can be a bit more helpful with this method, so long as you take your time and drill as straight as you can.

If you have a drill press, you will get a more precise holes, but I didn't fire up my drill press with both the miter gauge style and sled style jig (I did make both of them) and using just a drill worked fine for me. Then again, skill does play into this with a hand drill (and believe me, I'm no Bob Vila).

We'll want to cut the board so that that piece will sit flush in the channel. You can use either your sled or the miter gauge to do so. Once we've cut the one, we'll repeat the process and cut 2 more, the exact way.

Next we'll cut our pin out, which is basically the same thing as the three blocks, except it will extend another inch above the jig, giving it a measurement of 2" in length. Just as the previous stop blocks, we'll want to measure and mark an 'X' on the lower 1" section. The hole in this block will be drilled out with a 1/2" Forstner bit as it will need to house the 3/8" Brad t-nut.

Finally, we'll cut the pin (again, making sure we've added an inch) and move onto the next step.

Stop Blocked and Pinned.

Step 6: Sanding and Epoxy, Oh Great Pin

A couple points about our great, reliable pin. The actual size of the barrel on the brad t-nut is 7/16". But, if you remember, we drilled the hole at 1/2". Because it's important that it's both straight on the threaded rod and in the right space, we gave ourselves a 1/16" extra. We'll now center it exactly where it needs to be by allowing it to be threaded on and glued in place.

Before we do that, we'll want to make sure that it slides easily inside of the dado. To do that we'll use a piece of sandpaper and do our best to sand both edges evenly. This is a simple affair that doesn't need to be overdone or underdone...like a tasty, medium steak. In the video link I'm providing here, you'll get the essential idea of how much it needs to slide.

Smooth slidin'.

After we've taken care to allow play in the pin's movement, we'll work on epoxying the brad t-nut in place. To do that, we'll first lay down three strips of masking tape in the dado so that our epoxy doesn't somehow drip down into the valley. Since we're only epoxying the pin, one might ask why we don't just use a strip of tape under it instead of adding tape below both stop blocks. The reason is simple. Adding tape will raise the pin a slight bit above the wood channel. We'll add pieces of tape on the underside of the other 2 stop blocks to keep the same height.

We'll put the stop blocks about where they'll be when this is all assembled: one on the left side and the other on the right side of the kerf cut we made in step 4. The 3rd block will play no part in this step. The pin will need to be somewhere between the two pins and the brad t-nut will need to be threaded on.

Adding tape.

Next we'll mix a little bit of epoxy up and place it on the barrel of the brad t-nut being extremely careful not to get any on the threading. We'll squeeze the block on and check to make sure its snug and give it about 30 minutes to harden. Note that it won't be fully cured at that point, but enough for us to do the next step.

Last, but not least, mark both of the stop blocks with an arrow pointing up, just in case flipping the blocks over in the future gives us a different angle.

Nature's magic glue.

Step 7: Finishing Our Box Joint Mechanism

Now that our pin has somewhat cured (if you waited 30 minutes (if you waited longer, you're better than I)), we'll move our mechanism out of the dado and remove the tape. Things are about to get critically important.

Well, sort of. This is a simple project, but this part is important if we want our mechanism to work.

We'll make sure that the stop block next to the kerf is about a half inch over to the right of the kerf* and the stop block on the opposite side is about a nut's length away from the end. Also make sure that the threaded rod is about a 1/2" outside of the jig as we'll be adding a crank to the end. We'll add a washer and a 3/8" nut to both sides, leaving absolutely no space between the wood and the washer. This mechanism (the threaded rod) needs to not move at all.

Once we've placed the rod exactly where it needs to be, we'll mark the rod next to the nut. This mark will tell us how far to return the nut after we've put epoxy on the rod, so take some mental pictures of the position.

Remove the mechanism, pushing both stop washers and stop blocks towards the center and roll back the nuts about a half inch. We'll put epoxy where both nuts had been on the rod and roll the nuts back, again, checking the marks we made to make sure they're where they need to be. Now we'll wait another 30 minutes for the epoxy to semi-cure.

* By right, I mean if the cut dado is facing forward and you are behind the back of the board.

Positioning the mechanism.

After the initial set up time we'll add a little glue to the blocks and reposition them back into the track. We'll now add the 3rd stop block at the far end which will be used to close up the channel and prevent warping. You may find that the stop blocks are a bit more difficult to insert and may require a mallet or a hammer. Expansion and all.

Now give it about 5 hours before proceeding.

Gluing and allowing our mechanism break time.

Step 8: Cranky Crank

Technically speaking, this project is...done. So long as you don't mind moving the bolt with your fingers to advance the pin. If tedious finger twisting and frustration due to lack of indexing isn't your style, then let's add ourselves a crank. It'll be a simple, I promise!

We're heading back now to the 1" block we cut from the 1x4x20". We'll be cutting a 2" piece off of this, but before we do we're going to drill out a hole for our 1/4" bolt and a pronged t-nut. Both holes we'll drill will be 1/2" from the edge of the 2" piece. One, of course, will be a 1/4" hole, the other we'll use the 1/2" forstner bit.

Once both are drilled, we'll put our pronged t-nut in the hole and give it a couple smacks to imprint holes into the wood below it. Next we'll use an 1/8" drill bit and drill all 3 (sometimes 4 holes depending on your t-nut) holes. Afterwards, we'll bring it back to the table saw and cut the 2" crank segment off.

We'll add epoxy to the underside of the 1/4" carriage bolt head and hammer it into the 1/4" hole we drilled. I added a little epoxy to the under side of the pronged t-nut just to make sure it was flat against the wood and gave it 30 minutes to set.

Next I turned the jig on its end and poured epoxy into the 1/2" hole, opposite of the t-nut entrance. This will glue and permanently lock up the threaded rod to the crank. Be sure to wait for the epoxy to cure before using.

Now, you could crank the cranky crank with just the 1/4" bolt, but it's not very ergonomically pleasing on the fingers. So we'll build a tiny handle by once again going back to the 1" block we cut from the 1x4x20". We'll cut off a 1" section (dimensions 1x1x 3/4" block) and turn it on it's side, placing an 'X' and drilling through. We'll add a 1/4" washer between the 2" crank and the handle for the crank, another washer on the opposite side of the handle, and then (2) 1/4" nuts that are jammed together to form a lock. Alternatively, you could just use one, so long as you use epoxy to set that one.

We're done!

Making and installing the cranky crank.

Step 9: Operation

Just like every tool in your shop, there's a little bit of learning that's involved in making a perfect box joint cut. Fortunately for you, I've spent a significant amount of time studying my jig to give you the advice and information I'm going to give you to fine tune your jig.

In this step, I'm going to be as thorough as I know how to be. I'm not always the best when I describe something, so PLEASE leave a message at the bottom of this instructable if you have ANY questions. I want this to be a generally enjoyable experience for you and want it to work for every person that puts this jig together. It's not a difficult jig at all to make (I've made 4 of these jigs now, and each works beautifully), but I may have not made certain things clear that I'll clear up as soon as I'm told.

If you haven't watched the video, here are the instructions for operation that I give in it:

Operation of your new box joint jig.

Now that you've seen it, there are a few corrections I'd like to give as explaining on videos can be difficult due to attention spans and all. Using those full instructions will give you a box joint. Absolutely! But it will be a very loose fitting joint. For some people, that's great; other's, it could be annoying. There are a few ways to fix this annoyance. First, I'll give the basic operation and then I'll fine tune it for you.

First and foremost, we'll need to line up the tooth of our blade to be on the inside of our board, at the very beginning. In "Picture A", you can see how my stock is positioned according to the blade. As soon as I made the right alignment, I marked a line on the pin and the jig itself for quick future references (as seen in "Picture B"). I also made sure that my crank, at that line, was in either an up or down position to make it easier for future turning. Now, I don't know if I somehow got lucky and each of the 4 box joint jigs I've made have allowed me to, through some cosmic randomness, have it line up in either the up or down position. (Pictures "Crank Position Up/Down") above)

Now I'll start my saw and make my first cut. I'll crank it again, and make a second cut. From here, you can make any series of cuts, but you have to start off with at least 2 cuts. Once you've decided the number of cranks you want to make each tooth, you'll put your second board on, lined up to the last cut that was made ("Picture C").

Of course, for every cut group we make, we'll need to make a 'non cut' group. To start on this new group, we'll add 2 turns. So the pattern is as follows

Cut group
Non cut group + 2 turns

For example, if I make my first initial 2 cut pass, I'll need to do 2 non cuts, plus 2 more turns.

2 cutting turns
4 non cutting turns

For 7 cuts, I'll need to make 9 non cuts.

7 cutting turns
9 non cutting turns

Now back to the fitting issue. If you find that your cuts aren't tight enough for you, the last crank you make before switching to a non cutting cycle should be a half turn.

Going back to the past examples:

2 cutting turns = 1 1/2 cranks
4 non cutting turns (stays the same)
7 cutting turns = 6 1/2 cutting turns
9 non cutting turns (stays the same)

But why is the joint loose? Since most 10" blades for table saws are roughly 3/32" in cutting width (the kerf), and our 3/8"-16 rod moves at a 1/16 of an inch with every crank rotation we make, I used 2 turns to overcome the 3/32". Two turns of a 3/8"-16 rod actually comes to 4/16", or 1/8", leaving 1/16", or about 1/32" on either side of the tooth. To tighten the tooth, we could use a 1/16" blade in place of our 3/32" blade, or go back to my last example by using a half crank.

Here I'm giving credit to Mathias Wandel for the idea of using a couple of 1/16" blades stacked together.

Step 10: Advanced!

I've made a very sleek and rugged little table saw sled where I incorporated this mechanism into the fence as well as adding additional details. If you'd like to see how I did that, check out the link below.

Advanced Box Sled

Another idea that I incorporated into my jig is a clamping board that allows you to clamp your stock to a board that is glued to the pin. This makes it much easier to keep the boards straight as you'll be removing the human error aspect to pushing the board along.

I've left a sketchup image I made that I used on my jig. Of course, this was cut on a bandsaw, something I said you didn't need to make box joints. You, of course, could use a coping saw if you don't have access to a bandsaw. The image I've left makes it very easy to make your own clamping board to add to your jig.

Clamping board addition.

Step 11: Troubleshooting & Thank You!

My joints aren't tight enough.

Check out my "Operation" step which will explain how to get tighter cuts.

I'm having trouble with my teeth not looking right/lining up when I'm done.

Be absolutely sure that your stock is perfectly straight (all corners are 90°) and that it is aligned up properly to the pin. Also make sure that your sled is flat and not sagging or raised in the middle. I had difficulty with one of my sleds until I found out it wasn't flat.


Please leave me more problems (if you run into anything) so that I can add them to the troubleshooting comments above!

Thank you so much for giving this idea of mine a look. I had a blast making this and would be thrilled to hear that you've made it yourself, so please hit the "I made it!" button. If you choose to make this project, please give me credit for the idea. Taking other people's ideas and calling them your own is a super naughty fib. A TON of time and energy went into this (at least a month's worth of time) so I'd appreciate a mention when using it.

If you like my work, please follow me here and on Instagram, as well as a sub on Youtube. Thank you!

YouTube

Instagram

2 People Made This Project!

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28 Comments

0
lstanczyk
lstanczyk

Question 1 year ago on Step 11

I can't get my numbers to work. I used 1/4-20 rod. It takes 2 rotation to make the blade width. So I add 4 to my non cuts. Still no dice. What am I doing wrong?

0
Make_Things
Make_Things

Answer 1 year ago

Ugh! I know the feeling.

Because I’ve never used a 1/4-20, I can only guess. Have you tried doing 1/2 rotations? But wait, is it too big or too little (the non cuts)?

0
emmittgabbard
emmittgabbard

Reply 5 months ago

1/4-20 is 20 threads to an inch, so if you do the math, 10 turns (threads) is 1/2 inch. 5 threads (turns) is 1/4 inch, 2 1/2 turns (threads) is 1/8 inch. I will use 3/8-16 where every complete turn is 1/16th of and inch, easy math.

0
lstanczyk
lstanczyk

Reply 1 year ago

The non cuts are too big and offset. First if offset one blade width, second is 2 blade widths.

What was your methodology to figure the numbers out? Trial and error?

0
Make_Things
Make_Things

Reply 1 year ago

What is the kerf of your blade? If you’re using a 3/8-16 rod, every turn will be a 1/16”. Most blades are thin kerf in the stores (at least around me) and are 3/32” wide. 3/32” wide is almost 2 spins with a 3/8-16 rod. If you use the full 2 spins, you’ll have an extra 1/32” of space for each side of a tooth.

Some people like a loose joint...and that is most certainly a loose joint. I like to do a half crank on the end of my last cut which eliminates the 1/32” and gives you a nice tight joint.

So say I want a 5 turn tooth. On the last twist I do a half. In essence it’s 4 1/2” cut turns and 2 non cut turns.

If you’re using a 1/4-20 rod...you’re in untamed waters. I’ve used a 5/16-18 rod...which was doable but difficult.

0
ptofimpact
ptofimpact

7 months ago

Very nice , working on one now. Excellent Video, and Instructions, Thanks!

0
Make_Things
Make_Things

Reply 7 months ago

Thank you for your comment! Do me a huge favor and hit the "I made it!" as well as sending me a picture. I absolutely LOVE seeing what others come up with when they do these projects!

0
ptofimpact
ptofimpact

Reply 6 months ago

I am still working on it, but will do so when Finished. The Pin that moves/indexes, I used a piece of Cherry a bit stronger

0
Make_Things
Make_Things

Reply 6 months ago

This is fantastic...you've made my day! Thank you so much for sharing and I LOVE it!

0
cliffhamilton
cliffhamilton

Question 1 year ago

Great Instructable! Do you also have metric measurements?

0
Make_Things
Make_Things

Answer 1 year ago

I really tried to do that at the beginning when I came to instructables, but the amount of research I did was absurd and often times I felt like items were so different to localities that I really didn’t feel like I was doing much good.

For example: I used a 3/8-16 threaded rod in this project. In America, that’s very common. I could probably hit any local store and pick one up. But how does that translate to a metric rod in Australia? What’s the TPI (I don’t know what you call that in the metric system).

If you want to translate I would be more than happy to add it...but it’s a lot of work.

1
nedchurch
nedchurch

Reply 1 year ago

Try 1mm pitch 8mm rod (that would be 8mm fine thread) - that should give you 1mm per turn which should give you a high degree of accuracy) I think Bunnings stocks it. Otherwise 8mm std thread is 1.25mm pitch and needs more thinking about to work out the distance/turns.

0
Make_Things
Make_Things

Reply 1 year ago

That’s very interesting...anything that equals 10mm though? Say a 6mm/10mm rod with a 1mm pitch? That would work the best to keep things aligned with the (10’s) metric system.

0
nedchurch
nedchurch

Reply 1 year ago

I think the 10mm diameter which is closer to 3/8 inch is "superfine" when it has a 1mm pitch. Definitely easier to work with than imperial measurements

0
Make_Things
Make_Things

Reply 1 year ago

I'm all in favor of using MM, so long as it's a standard in my country and in local box stores. I'm not really worried so much about the diameter, but the threads per cm (is that correct?), like TPI. Since the imperial system uses 1/16", and a 3/8-16 threaded rod has 16 TPI, each crank I make is a 1/16 of an inch.

What I'm wondering is if there's a 1/10 threads per cm. That would make it incredibly easy to work with. Each crank would then equal a millimeter.

1
nedchurch
nedchurch

Reply 1 year ago

That would be 1mm pitch I.e. 10 threads per cm

0
Make_Things
Make_Things

Reply 1 year ago

Okay, I’m an 1diot. That totally makes sense and is indeed much simpler.

0
nedchurch
nedchurch

Reply 1 year ago

No you're not an idiot. Even though I've been using metric since the 1960s I still occasionally estimate in imperial but I hate working in it now and convert evrything to metric. I've used a 1mm pitch 10mm rod for my router lifter and it makes calculations much simpler.

0
Make_Things
Make_Things

Reply 1 year ago

Thanks. I take it you’re /not/ in the United States then? Or are you a hopeless rebel?

I’ve thought about converting my woodworking shop to the metric system (as it would be far easier) but it would be impossible now as my core audience is in the US.

Thanks for the discussion. I’ve learned something today!

0
nedchurch
nedchurch

Reply 1 year ago

No not US, New Zealand. Everything is metric and it sure makes life easier. I can remember doing long division of feet and inches. You have great ideas and I'm sure you could het the USA to change to metric...it makes physics much easier. :)