Laser Cut Boxes With Finger Joints, Understanding All the Settings

Making boxes is one of the most satisfying (and useful) things you can do with a laser cutter, and there are a ton of box generators out there to choose from. I think most of them share some basic concepts and I wanted to explain those in detail.

For the embedded video and this Instructable I'm using this web-based open box generator made with Cuttle.xyz but I think the explanations are applicable to any other generator or even for making your own designs.

For a comprehensive list of box generators check out SparkItUp's The Ultimate Guide to Laser-cut Box Generators, it's a wonderful display of variety and a helpful tool to help you choose something that will fit your needs.

These are the options we'll explore in depth:

1. Size (width, depth and height)
2. Material Thickness
3. Kerf Compensation
4. Tab Width

The names width, depth and height are analogous to the X,Y and Z axes in 3 dimensional space. Width and depth are somewhat interchangeable but in some cases, like in the open box in the picture, the height refers to the distance between the opening and the bottom surface.

When it comes to choosing the size of your box you need to take into account wether you are looking for the outside dimensions or the inside dimensions. If you have a space where your box will go, then the outside dimensions are important, but if you want to fit something inside the box, you need to pay attention to the inside dimensions.

In the generator above you enter the outside dimensions which incorporate the material thickness, but if you need to know the inside dimensions you can look at the callout highlighted in green at the bottom.

The thickness of your material matters because it determines the length of the interlocking edges. For really clean looking corners you want to be fairly precise when measuring the thickness of your material.

If you make you material thickness parameter a bit more than your actual material, this isn't a big deal. It means the joints will protrude slightly from the corners. You can sand these down or even make exaggerated versions because they can look kind of cool.

Conversely, making them too short actually makes it hard to assemble the box, so err on the side of too big if you can.

Measuring Material Thickness

A pair of calipers is the most common tool used for measuring the thickness of your material. There are some great guides for using caliper's on Instructables like this one or check out this short video.

When measuring flat materials for making boxes take these considerations into account:

• Pay attention that the jaws of your calipers are parallel to the material.
• If the material comes with some kind of protective film, remove it before you measure.
• Most flat materials like plywood or acrylic are not perfectly consistent in their thickness, so take several measurements and choose a reasonable average.

Kerf is a fancy word for the the groove or slit created by cutting or sawing something. Woodworkers use the term to talk about the size of the groove left by a saw blade. Laser cutters also leave a groove when vaporizing materials and this affects the dimensions of the final product.

With a saw the kerf is very consistent and very close to the actual width of the blade, but with a laser cutter the kerf will vary a lot depending on the interaction of the material, machine, and settings used.

This loss of material mostly affects projects where you want to fit things together with some precision. In our case we want the fit between the box faces to be not too loose, not too tight.

Compensating for this loss of material when cutting is usually done by moving the cut line to roughly match the loss. In practice the actual amount will also vary, and you'll find it mostly via trial and error.

This means it's good to start by trying the suggested kerf compensation amount (0.007 inches) and cut two faces of the box as a test. And if it's too tight reduce it a little bit (say to 0.006") and test it again. If it's too loose with your material and machine increase it by a little bit (say to 0.008").

The thing to remember is: bigger kerf value = tighter fit

The Tab Width option determines the size of the interlocking sections. If you make the tab width smaller you get more tabs and increase cutting time. Up to a point this makes a stronger box, but too many tabs can also weaken the edges.

Conversely making bigger tabs means fewer of them, the limit here is to leave enough material in the corner to support the tab.

Within these two extremes (large, fewer tabs and more, smaller tabs) the choice here is almost aesthetic. Choose something that looks balanced depending on the size of your box.

The layout diagram is helpful when assembling the box. I like to place the bottom on the table and then assemble opposing faces in pairs, for example left and right and front and back.

Glue or No Glue?

Some materials like Plywood and MDF work fine without glue if you get a nice tight fit. This is also known as a "friction fit", make sure to gently tap the box with a mallet to get all the faces to hold together.

If the fit is a bit looser, or you are going to handle the box a lot, glue is a great idea. Generic wood glue or Elmer's works well on wood boxes.

Acrylic can work well with short term projects with CA glue (also known as super glue) but do some testing beforehand because some CA glues will cause hazing on the material, and some will become brittle overtime. A better option would be a specialized solvent for "welding" acrylics such as WELD-ON acrylic adhesive.

Hopefully this is a helpful summary that clarifies some of the terminology found in box generators. You will find the Open Box Generator and other variations on box generators at cuttle.xyz/templates.

Have fun making your own boxes!