Battery storage box

I have a lot of batteries lying around and always forget which rechargeable batteries are full and which are empty. So I made this small storage box to keep the batteries in.

Design:
I’ve designed it using solvespace. It is a simple parametric sketching CAD program. So first you sketch the object with line segments and arcs and subsequently you give it the right shape by adding constraints. It has a bit of learning curve, but it’s worth it. Being able to sketch parts in 2d and then piece them together in 3d to see what the result looks like is just really useful. And if something doesn’t seem right you can go back and change a few parameters, rather than having to redraw the entire thing again.

There are differences in the size of batteries. Some are 4/5cm long, others only 3cm. For those short batteries I created small pieces of wood that are positioned between the bottom and top plate, so the batteries can stand on it. I’ve cut some small 3×3mm squares in those plates where those small pieces of wood could be put in.

Rounded corners (lattice):
I like using rounded corners. Not ony do they look nice, but they also allow the box to be put together without using any glue or screws. The little bit of tension in the corners keeps everything in place. As the radius I chose 3cm. For smaller radii, you probably would need to make the wood a bit wet to bend it that tightly. The width of the lattice then becomes ½ × 30mm × π = 47.12mm.

I wanted to have the 3cm radius (6cm diameter) end in the middle of the wood. So I would have an inner diameter of ø57mm and outer diameter of ø63mm. This is shown in the picture below. However, I accidentally picked ø58.5mm as inner diameter. I’m not sure whether ø57mm would have provided enough tension to keep the box in shape without glue.

There is no way to draw the lattice pattern in solvespace, so I drew them in Inkscape. I used the ‘create tiled clones…’ option, though it would’ve been easier to copy paste the lines manually. In solvespace I broke the lattice line in 2 to get a snapping point that I could use to snap the lattice pattern to when adding it in Inkscape.

Text:
I’ve added the text (‘AA’, ‘9V’, ‘N/LR1′, etc.) using Inkscape’s Hershey text. Choose Extensions > Render > Hershey Text…, write the text and click apply. The text consists of straight line segments. To make them into round segments, use Path > Simplify (Ctrl+L).

Model:

Cutting:
I set the focus of the laser to -1.8mm. For cutting I used speed 28 and power 100. For writing the text I used speed 400 and power 5. For some reason the focus changes when the laser moves around in the cutting area, which caused some pieces to not be cut out properly. I could still break them out though.

Assembly:
It turned out that the wood I used was more like 3.3mm thick, rather than the 3mm I designed it for. This caused the holes in the side to be slightly too small. I fixed this by shaving off a bit from the connectors using sandpaper. I also accidentally cut the parts out of wood that was covered with a sticker, so I used the sandpaper to remove those as well.