## Introduction: Laser Cut Calculator Caddy

I wanted a calculator caddy that was easy to produce and assemble (requiring as little glue or other fiddly joinery as possible), sturdy enough for "grab and go," and dirt cheap. I like the challenges of the "flat pack" style of design, and am very happy with this solution. I used a CNC laser cutter to cut the pieces from 3mm MDF, which is very cheap. The same design should also work with other 3mm laser cut materials, like acrylic. The parts can be nested onto large sheets of material to produce many of these caddies at once. If you're good at drawing up vectors precisely, you should be able to adapt this design to carry all kinds of things!

## Step 1: Design the Parts and Draw the Vectors

This is the most time-consuming and difficult part of the project, but once you've done this well your laser cutter will do the rest, and you can make as many as you like. I used Vectric VCarve Pro, as I find it to be a pretty friendly tool for this kind of work. If I ever find the time, I'd like to make this design fully parametric, perhaps in Fusion 360, so you could simply specify the dimensions and numbers of compartments and have the vectors for the parts automatically generated. Actually, maybe you could do that!

The drawing shows the 6 parts involved, and how many of each are needed. The light red lines show some of the important alignments between the parts. There are also 3 coloured dimensions (red, green, blue) which appear in several places on the drawing. These correspond to the dimensions shown in the photo of the assembled caddy, and are the internal dimensions of the compartments you end up with. Hopefully by looking at these key dimensions you will gain some insight into how to draw the parts correctly. Joining the parts together and keeping them in place is all based on hooks, tabs, and slots, with a very small amount of glue at the end. There's probably a lot to say about how to make these features all work together, but overall you just need to engage your spatial reasoning skills, always draw the vectors precisely and correctly aligned to each other, and keep the assembly process in mind!

Once I knew I wanted to enclose the calculators on all sides, my next decision was based on making sure they were supported from below. I knew everything was going to be hanging from the spine piece when it was carried by the handle, so I put my first set of hooks on the bottom of the spine piece. These hooks fit into the slots on the bottom piece, holding it up. Everything else more or less fell into place around that initial design decision: the hooks on the ends of the spine piece are facing upwards because the end pieces are hanging from the spine, the side pieces have downward-facing hooks because they are hanging from the end pieces, and so they in turn can also provide support to the bottom piece via their lower hooks.

I drew the vectors in their final alignment, in other words in the relative positions they would be in once the hooks were engaged in their slots. This made it easier for me to visualize what I was doing and check that everything "made sense." There are a number of little details to consider. For example, the slots on the side pieces needed to be longer than the tabs on the dividers in order to accommodate the side pieces sliding downward into place during assembly. Keeping everything aligned in your vector drawing software makes it easier to notice details like this and respond to them. Another little detail is that the central slots on the end pieces are 3.5mm rather than 3mm; the extra half a millimetre allows for a little play in the end pieces, as they have to be spread apart during the assembly process when the side pieces go on.

The final product holds together in a very satisfying way, with the pieces mutually supporting each other and maintaining the integrity of the whole.

## Step 2: Assembly Part 1

I don't have any images of the laser cutter doing its work, but I'm sure yours will do fine, or you can have someone else cut them for you. Be sure your material is 3mm thick. Begin assembly as shown in the images. The 7 dividers slide onto the spine fully. End piece B slides onto the hooks on the end of the spine, with the bottom hooks on the spine facing away from it. The long slots of end piece B are towards the bottom. End piece A slides onto the other end of the spine, with the "cut off" end towards the bottom.

## Step 3: Assembly Part 2

Fit on the side pieces, one at a time. The end pieces need to be spread in order to get both sets of hooks into their slots. You shouldn't have to flex the material much, so it won't be in danger of breaking. The tabs on the dividers need to go into the slots on the side pieces. Make sure the hooks on the bottoms of both side pieces are facing the same direction as the bottom hooks of the spine piece. It should come together without having to apply force if you follow what the images show. All hooks should be fully engaged in their slots before proceeding.

## Step 4: Assembly Part 3

Make sure the side pieces are fully pushed downward into the end pieces, and that the end pieces are fully pushed downward onto the spine. This should leave a space for the bottom piece to slide into, engaging with all the hooks on the spine and both side pieces. The tabs on the bottom piece will slip into the slots on end piece B. Apply glue to the thin "ledge" which is formed between end piece A and the bottom piece on the outside of the caddy. I used a simple PVA wood glue. Its only job is to keep the bottom piece from sliding back out, so it doesn't take much, just run a couple of beads along the ledge. You could alter this design to have a small screw or two pushed into this ledge from above to do the same job. Once the glue is dry your calculator caddy is good to go!

Participated in the
CNC Contest 2020