Introduction: How to Build a Variable Box Joint Jig
This box joint jig is really cool since it enables you to cut different sized box joints using a single blade. It's relatively easy to put together and it works really well. This jig is an attachment to my previous table saw cross cut sled, which I've made a very detailed Instructable about: How To Make a Cross Cut Sled. You can either add on to that sled using these specific parts and dimensions, or you can use the general concepts and ideas and add on to your existing table saw sled.
Step 1: What You'll Need:
Now, I'm using 1/2" Baltic birch plywood to create the box joint addition.
You'll need the following cuts.
- A) 18 x 1 "
- B) 9 1/2 x 2 3/4 "
- C) 9 1/2 x 2 1/4 "
- D) 8 1/2 x 2 1/4 "
- E) 9 1/2 x 2 "
You'll also need:
- 1 @ 3/8 " rod, 16 threads per inch, 24 " long
- 2 @ 5/16 " machine screws, 4" long
- 1 @ 1/4-20 machine screw, 2" long
In terms of hardware, you'll need:
- 1 @ 3/8 " pronged tee nut
- 2 @ 5/16 " pronged tee nut
- 1 @ 3/8 " cap nut
- 5 @ 3/8 " washer
- 2 @ 1/4 " washer
- 2 @ 3/8 " nut
- 2 @ 1/4 " nut
- 1 1/4 " screws
Step 2: Additional Parts: Wheel, Spacer
Now, in order to build the jig, you will need a couple of additional parts. First of all, you will need a piece that turns.
On my prototype model I just used a piece of plywood so you don't have to do anything fancy, however I thought it would be nice with a round wheel so I cut up these pieces on the x carve which I glued together to make a thicker piece.
I'm also going to need a spacer to connect to the rod, so I cut one up on the lathe that I drilled all the way through with a 3/8" bit. Totally it measures 4 inches long by about 1 inches in diameter, however you can make yours whatever size you want.
Step 3: Knobs, Block, Handle
Now I'm also going to need some knobs. However again, you see on my prototype here I simply used two square pieces of plywood which works, but I decided to do something a little nicer. So I made a circle, drilled 3/4 inch holes in the corners, and then cut out the circle in between on the bandsaw.
Then I sanded, drilled a 3/8 inch hole all the way through and out hammered in the 5/16 inch pronged tee nut in the center of each knob. I read about this technique of making knobs in a woodworking magainze, but I can't remember where. Worked out great.
Next I need a piece of hardwood to attach to the rod in the back. This is maple and measures 2 x 2 x 2 3/4 inches. You could always glue together a few hardwood pieces to create this dimension
And then lastly I'm going to need another piece to hold on to as you spin the rod. Again on my prototype I just used a piece of scrap wood, however I thought it would be nice with a round smooth handle, so I turned it on the lathe.
Then I drilled a shallow hole, and epoxied in this 1/4 20 machine screw. It measures 2 1/2 inches long and about 1 inch in diameter, however you could make it any size you want.
And those were all the additional pieces.
Step 4: Assemble
Now we're ready to assemble.
First off all, let's remove the aluminum clamp bracket on the front fence.
Next we're going to take piece A, fit it in the center and screw it down, make sure to pre-drill ahead of time.
Now, let's get piece D, and the hardwood block. First, let's place piece D next to the fence, and push the block against it for spacing. Now bring the block up so it's level with the fence, bring a pencil through the hole, and mark the space on the block.
That mark shows you where you need to drill through using a 3/8 inch bit. Then, hammer in the 3/8 inch pronged tee nut. Disregard the other hole next to it in the picture, I drilled in the wrong position initially. I also placed two 3/4 inch screws next to the nut, to keep it in place.
Once the block is prepared, place cut D in the center, line up the block, and screw the plywood to the hardwood, making sure everything is positioned right.
Next, push the rod through the hole in side fence (which we already drilled when making the sled), then through the block and out through the other side fence.
Get the cap nut and a 3/8 inch washer, put it on the rod and screw in the nut.
Now, get a pair of pliers and hold the rod tight, while tightening the cap. Next, get another washer, put in on the other end, put on the spacer, another washer, and a 3/8 " nut. Another washer, then put on the wheel, another washer, and then another 3/8 " nut.
To tighten this, hold the in between nut with a pair of pliers, and then tighten by hand on the end, and then tighten with a wrench. It's important that you're not tightening the entire rod here, you want to secure the wheel in place.
Now the carriage moves when you turn the wheel. You want to make sure there's no slack from one end of the rod to the other. If there is, take that part, push this nut down a bit further and tighten again.
You want to make sure that the wheel is good and tight in between those two nuts, because over time as you spin this it can loosen.
Step 5: Handle & Wheel
Now, let's get the handle, put on a 1/4 inch washer, put the screw attached to the handle through the hole in the wheel, add another washer and then screw on the two 1/4 inch nuts.
One nut acts as a stopper to the other. So you want to hold the one closest to the wheel, and tighten the other one with a wrench. Now this will determine how tight the handle goes on the wheel, and you don't want the handle on the wheel too too tight, you want to be able to spin it.
Now let's spin the carriage all the way back. Let's get piece E, and rest it on the fence and piece D which is screwed into the block. Make sure to position it right and screw down on piece D, making sure to pre-drill ahead of time.
Step 6: Carriage
To prepare piece C, you'll need to drill two 5/16 inch holes in the middle, about 1 1/2 inches from each side. Also, chisel out enough space to fit the head of the 5/15 inch screws. This is how this will work: You'll insert the screws, make sure they fit flush. Then position the board in between piece A and piece E. And now you can continue securing piece E on the top and screw it down.
Now let's prepare piece B. Drill two 5/16 inch holes, each 1 1/8 inch from the long side, and 1 1/2 inches from the short side.Then slip it on to the carriage, making sure to have the right side up, and then thread on the knobs. Now as you turn the wheel, the whole carriage will move along with it. To finish the jig, I'm putting wax polish on the hardwood and on the rods. I'm also going to finish the new plywood pieces with wipe on poly to protect them from the elements.
Step 7: Using the Jig - 1/8 Inch
Now what's really awesome about this jig is the fact that you can create any sized box joints you want, you just have to adjust how you use it.
Let's start with the simplest joint, which is 1/8th of an inch.
First of all, make sure the carriage is positioned to the left. Also, make sure the handle is positioned up, this will be your reference point when you spin later.
If you want to cut two pieces of wood that fit flush into each other, then you need to space them out evenly. I've found it's a lot easier to create a spacer for each sized joint. Actually, for the 1/8th inch joint, I have a spacer that measures 3/32, that's because that's the thickness of the blade, I know it sounds a little confusing, but that's because it's not literally an 1/8 inch joint, it's actually a 3/32 inch joint, since that's the width of the blade. Now if your blade is 1/8 of an inch, then you should make the spacer that distance.
You could also measure out the distance 3/32, or the width of your blade and make a mark if you don't have a spacer, and line up your pieces from there. So set up the pieces with a spacer, tighten the knobs and then remove the spacer.
Also make sure the blade is just a snippet higher than the thickness of your wood.
Now for 1/8 of inch joint, you need to cut once, and then spin three times. Cut again, and then spin three times and so on. You can stack several pieces of wood and cut them all at once, especially when you're cutting thin pieces of wood like this.
When you're done, loosen the knobs and check if they fit, which they should, if you counted correctly and made sure the handle was always in the up position after each spin or cut.
Step 8: 1/4 Inch Joint
Let's move on to the 1/4 inch joint.
So for a 1/4 inch, the offset needs to be 1/4 in order for it to be right. So again, either mark out on the piece, or make a spacer that you can re-use. So arrange correctly, and then start cutting.
For a 1/4 inch joint the pattern is this: cut four times, with a spin in between each cut to move it forward. Then spin six times. Then cut four times, spin six times and so forth.
Step 9: 1/2 Inch Joint
Now for the 1/2 inch joint.
Again, make sure the handle is pointing upwards. Also, this is true for each joint, make sure the height of the blade is just a touch above the thickness of the wood you're cutting.
For a 1/2 inch joint, I have a spacer measuring 1/2 inch. So setting up the wood up with the spacer, and here you can see that you need to place them just before the cutting mark here. If this is a little off you won't have as tight a fit. Then remove the spacer and tighten.
Now 1/2 an inch is a little different, in the sense that you need to start counting your first cut on two. So you do your first cut, and count that as two cuts initially. So the pattern here is eight cuts, ten spins, eight cuts, ten spins. The only the initial cut counted as two. So right off the bat it's two, three, four, five, six, seven, eight. Count ten times, and then cut eight times, this time starting on one.
Step 10: Using the Jig
Using the jig can be a little confusing, however once you get the numbers right for each type of joint they're really easy to do, you just have to figure out the pattern, and stay on top of your counting. I usually count out loud to keep track.
Of course you could also create new patterns and be really creative, do any sizes that you want. So that is pretty cool.
Now this jig is meant to be taken off the cross cut sled, it's pretty easy to remove and put back on again, so you can use the sled to make cross cuts when you're not cutting box joints.
Also, these measurements are all based on imperial and very much related to the size of the rod you use. You could certainly do this in metric, however the spinning would be a little different depending on the size of the rod, so you would have to work those numbers out.
This jig is really easy for anyone to use. You don't need any technical expertise. So far for me, it's been very safe, however you should always be very careful with your table saw. I really like that you don't need many parts, it's not a complicated build, it's pretty easy, and it's very useful.
Step 11: Conclusion - Watch the Video
For a much better perspective, make sure to watch the detailed how-to video on how to build this cool jig!
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