Laser Cut Ambient Light With Kerf Bends

What this Instructable is:

This document is meant to be a broad set of instructions on how to create a battery-powered ambient light from an initial CAD model that has been designed with the intent to be lasercut. It also very briefly covers flexible kerf design with the intent of using it as decorative elements, and some thoughts on why I made this light the way I did.

What this Instructable is not:

These are not meant to be instructions on how to CAD model from scratch, nor is it a guide on best practices for lasercut designs or a mathematical analysis of flexible kerf design. I will also not be covering how to pick electrical components.

• Baltic Birch Plywood (3mm)
• Mulberry Paper (also known as Shoji Paper or Rice Paper)
• LiPo Battery
• Power Switch
• 5V LED Strip
• Stranded Wire
• (optional) Female Header

When designing laser cut objects, it's a good to go into the model with the consideration of how it will be eventually cut and constructed. Keep in mind the limitations of the material you're working with - the thickness of your sheet stock is important to remember, as it's not something that can be easily changed, outside of changing the source material entirely. It's much easier to nudge the dimension of a slot or tab during design than it is to shave off a millimeter off of plywood.

The second image shows the CAD model after splitting it into the various components. In this specific example, the colours are arbitrary and only exist for the sake of clarity to easily view the different parts. Note how at the top, I have intentionally left the left and right panels (orange and pink) slanted for ease of modeling. These slants will not be cut in the final model, as most lasers can only cut orthogonal/normal to the surface. The flexible elements have not been modeled yet - the areas where they will go have been put in, but the actual design of the kerf is created standalone.

Strictly speaking, a kerf is the gap left by a tool when cutting material, such as a sawblade, or in this case, a laser cutter. Most of the time, this gap is undesirable, as the kerf means that material is wasted, and the gap needs to be compensated for to make sure your project fits together properly.

However, in this case, we can take advantage of the kerf to create flexible parts from solid material. This is possible because the bending force is distributed along a much longer length than it would be if the material remained uncut. As an example, think of a plastic ruler - if you try to twist a short length, it would probably break because it's not flexible enough, but if you make the ruler 5 or 10 times as long, you would easily be able to twist it much more without breaking, as the torsional force is distributed. Something similar happens here, where we are redirecting the load along a much longer (and thus more flexible) path than it would follow if it was a solid sheet.

The first image with the "capsules" is the design I used for the sides of the lamp. I cut out much more material than I needed to because I wanted the light to shine through this kerf pattern. Compare this with the second pattern, which is used for the base, where there is no light - these can remain slits.

In addition, note the difference between the fourth and fifth image; the third pattern is the one I ended up using for the base, as the torsional element is much longer and bent much better.

Once you've finalized your design, it's time to cut. I opted to also lasercut the mulberry paper to prevent any human error and to ensure it fits well.

Carefully check if all of the kerf bends perform the way you expect - it's better to find out now that something isn't flexible enough or is missing a cut than down the line when you're doing final assembly.

After you've cut all your elements out, it's a good idea to check that they all fit together to avoid problems down the line. It's much easier to sand some slots or tabs down when it's all individual parts than when you've already got everything glued together.

Next up is gluing the mulberry paper to the flexible elements. The reason I used this kind of paper was because it looked and felt nicer than "regular" paper - this is the same type of material that's used in paper Japanese lamps. It has a slightly rough texture to it and diffuses light well; the fibers present in it also give it a nice variation throughout the sheet when lit.

I used a diluted mixture of Elmer's School Glue (white or clear works equally well) with enough water to make it runny, but thick enough to remain where I spread it and not wick into the paper too quickly. Due to the way I've designed the light, the paper will not be subject to any tension or compression and should not tear or buckle when it is put into place.

After I spread the glue mixture on the plywood, I carefully place the paper onto it. Avoid moving it around, as this can cause streaks or blotches in undesirable places, especially on the flexible elements, as they are very thin, where there's not a lot of distance between glued and visible areas.

For the front and back elements, I used a spacer the width of the gap to make sure I had the right distance between the left and right side, then glued the paper to them simultaneously. This way, the parts will be perfectly aligned and I won't need to take an extra step to glue the other half.

Weigh the plywood down with a thick, rigid sheet to ensure the paper remains flat - I used a 5mm piece of acrylic.

The electrical part for this project is pretty simple. It's a 5V LED strip connected to a female header using 2 wires; the header slides onto a switch, which is connected to a LiPo battery. Since it's a 3.7V LiPo, it doesn't fully light the 5V LEDs, but I deemed a slight dip in brightness acceptable to simplify the wiring and power.

I opted to use a female header soldered onto the LED strip wires so that I could easily remove the switch and replace it with something else down the line without having to cut or resolder - such as a USB power source.

The LED strip is mounted on an internal rib that does not touch the rest of the light. There is enough gap between it and any paper to diffuse the light - if it was too close, "hot spots" would appear and detract from the look.

Final check: Do you have all your parts? Do the lights work? Is the paper adhered to the plywood properly? Is the glue dry?

Many laser-cut projects tend to make use of tabs and slots to hold everything together without glue. Because the kerf bend expands slightly, and because of shape of the bend itself, it wasn't entirely practical to have such an arrangement here. I used the same glue mixture from before, dabbed on the edges of the kerf, and lightly clamped together. Make sure your kerf is behaving like you expect - I had to nudge it into the right spot because it was stretching a bit differently than I thought it would.

That's it. Enjoy your new light.

Planned improvements: Since this was largely a proof-of-concept to see how well the kerf behaved and check the properties of the paper, I didn't put too much emphasis on long-term power. A battery is a bit unwieldy in this case (I have to disconnect it to charge it, and partially disassemble the bottom to access it in the first place), so I plan to add a USB port to run off of external power. In case I do want to keep the battery, there is enough space in the base to include a charging circuit and an on/off button.