Making a Box Joint Keepsake Box on the CNC

Having a CNC machine in the shop opens up a lot of really cool possibilities, especially when it comes to precision, repeatability etc... and it's great for making boxes. This is a box with finger joints and a sliding lid, and I'm going to go through the whole process of making it step by step. There's also a full video of the process that goes into things in more details!

Step 1: Design

The very first thing to consider when it comes to CNC work is design. It's a good idea if you first of all know what wood you're working with. I'm using 1/4 inch white oak boards, which will influence my design choices.

Secondly, let's talk joinery. What kind of joinery are we going to use? I'm partial to box joints, or finger joints as they're called. I think they're great - they are functional, utilitarian, they look great ... and they can all be cut flat, as opposed to like dovetails, where you'd have to have one piece sitting upright and the other flat, there's just a lot more set up. Let's make the bottom inset to add stability. And for a lid, let's do the same design as the bottom, a sliding lid, in a groove, simple, beautiful.

OK box joints it is, how about sizes: I'm going to go with 1/2 inch size joints. I think that looks good, and I'm going to be used 1/4 inch hardwood,

Step 2: Software

I'm using Aspire by Vectric for the software, but the principles will be the same no matter what software you're using. I'm making a box that measures 5 1/2 by 4 1/2 inches and that's 3 inches high. So I'm going to make one side each complete with box joints and then copy it so I have two sides. Once I have made my box joints, which are half inch long and 1/4 inch deep, because that's the thickness of the wood, I'm making the grooves, the pockets for the top and the bottom to slide into.

I'm also adding these little round circles on the corners of the box joints, and I'm going to run those with a finer bit, a 1/16 inch bit. Now the front and the back sides are slightly different sizes the front is a little shorter because the lid sliding in and out. I also need a top and a bottom, the bottom is going to be just a touch smaller because the top is also going to be a lid going all the way out one one side, whereas the bottom sits inset. I'm also adding this little piece on the side here that I'm going to glue on to the lid here, it's going to make the box feel seamless and also provide a little handle to grab onto as you open and close the box.

Once I'm happy with all my pieces and I have doubled checked and made sure the sizes and everything is good, it's time to set the toolpaths, I'm also going to add some tabs so the pieces don't fly off as they're being cut, and then we can take the file to the machine.

Step 3: Test Cut

Whenever possible I like to cut a test cut first on some cheaper wood, that's not always an option. This time I'm using some 1/4 inch plywood, just to make sure all the design choices are right and it fits together well.

Step 4: Securing the Wood

When you're cutting thin stock on the CNC, it's a little more tricky to secure the wood properly. There's not enough room here for too much error. First of all, I secure a scrap piece of plywood so I don't have to worry about the bit accidentally cutting into my t tracks below. I secure the plywood using a corner clamp so I know it's perfectly straight.

I then add the wood on top of the plywood and secure it with little clamps towards the sides so the wood will be held in place.

Step 5: Setting Up the Machine

Once I've set the x,y and z axis, turned on the dust collection and made sure I have the right bit on, I run the machine. For the first cut I'm using an 1/8 inch bit. 1/8 inch bit: https://amzn.to/3mGcij1

Since I'm cutting through hardwood, I'm adjusting my speed a little slower than if I were cutting through plywood.

Step 6: Changing Bits

Once I've run through the program, I switch the bit to a 1/16 inch bit: https://amzn.to/38hDjku

This will allow me to get into the fine corners of the joints, and actually make pieces that fit together.

Step 7: Removing Tabs & Test Fitting

Once all the cuts are done, I remove the tabs with a mallet and a chisel, and do a quick test fit to make sure the pieces are correct.

Step 8: Glue Up

Next up, I glue together the main box part and glue in the inset lid. Sometimes you need a little tap with a mallet or squeeze with a clamp to get the joints to come together. Checking square once it's glued up.

Step 9: Final Touches

To get the lid to slide in a little easier, it's a good idea to handplane the edges which makes it a lot smoother. I'm also gluing on a top piece on the lid which acts as a little handle and also completes the look of the box.