- Laser Cut Technology -

At FabLab Puebla, our facility is equipped with three advanced CAM-five brand-name laser cutting machines. These machines utilize cutting-edge CO2 tube technology, which generates a laser beam through the electrical stimulation of a gas mixture predominantly composed of carbon dioxide. A series of mirrors and a focusing lens then precisely guide and focus this beam onto the material's surface, enabling intricate cutting, engraving, or marking through the processes of melting, burning, or vaporizing the material.

- Laser Machine Use -

Here are the three laser machine models we have in the fablab.

The American National Standard Institute (ANSI) considers Laser Cutters a class 1 laser based on ANSI Z136.1. These devices are safe when used as designed without manipulating the safety features. However this are some safety considerations to take into account.

Safety Measures

• DO NOT look directly into the laser beam.
• DO NOT modify or disable any safety features of the laser system.
• DO NOT operate the laser unless all covers are in place and interlocks are working properly.
• DO NOT remove material from the cutting bed before it cools down.
• DO NOT leave a laser cutter operating unattended.
• DO NOT use highly flammable materials, explosives, or materials that could produce toxic byproducts.
• DO NOT use a laser cutter with a malfunctioning exhaust system or a clogged air filter.
• Laser cutters emit an invisible, high-energy laser beam that can cause serious skin burns. Always turn off the laser when the door is open.

- Compatible Material List -

These machines can work with a wide array of materials, from soft fabrics like cotton and felt to hard substances like MDF, wood, and acrylic. The following tables provide a comprehensive guide for materials that the lasers can work with:

Material	Cut	Engrave	Notes
Wood	Yes	Yes	Plywood, MDF, and hardwoods work well. Avoid treated or resinous woods.
Acrylic	Yes	Yes	Cast acrylic is preferred over extruded for cleaner cuts and engraving.
Paper/Cardboard	Yes	Yes	Thin materials work best; thicker cardboard may require multiple passes.
Leather	Yes	Yes	Genuine leather works well; avoid synthetic leather (may melt or burn).
Fabric	Yes	Yes	Natural fabrics like cotton work best; synthetic fabrics may melt.
Glass	No	Yes	Engraving only; cutting is not possible due to glass's brittleness.
Metal	No	Yes	Engraving requires a fiber laser; CO2 lasers can mark with special coatings.
Stone	No	Yes	Engraving only; materials like marble, granite, and slate work well.
Rubber	Yes	Yes	Ideal for stamp making; avoid PVC-based rubbers (toxic fumes).
Cork	Yes	Yes	Easy to cut and engrave; great for custom coasters and crafts.
Foam	Yes	Yes	Avoid PVC-based foams (toxic fumes).
Plywood	Yes	Yes	Avoid plywood with formaldehyde-based adhesives.
Bamboo	Yes	Yes	Ensure it’s dry and free of resins.
Ceramic	No	Yes	Engraving only requires a specialized coating for CO2 lasers.
Carbon Fiber	No	Yes	Engraving only; cutting releases toxic fumes.

Material	Reason
PVC (Polyvinyl Chloride)	Releases toxic chlorine gas when cut or engraved, which is harmful to humans and the machine.
Polycarbonate	Melts easily, produces poor cuts, and releases harmful fumes.
ABS Plastic	Melts and releases toxic fumes (cyanide and other harmful gases).
HDPE (High-Density Polyethylene)	Melts, warps, and produces inconsistent results.
PETG (Polyethylene Terephthalate Glycol)	Melts and produces inconsistent cuts and engravings.
Fiberglass	Releases toxic fumes and can damage the laser cutter.
Epoxy Resins	Releases toxic fumes when cut or engraved.
Polypropylene	Melts and produces poor results; not suitable for laser processing.
Styrofoam	Catches fire easily and releases toxic fumes.
Neoprene	Releases toxic chlorine gas when cut or engraved.
Vinyl	Releases toxic chlorine gas and hydrochloric acid fumes.
PTFE (Teflon)	Releases toxic fumes that are harmful to humans and the machine.
Carbon Fiber	Cutting releases toxic fumes; only engraving is possible with caution.
Coated Materials	Many coatings (e.g., powder-coated metals) release toxic fumes when laser processed.
Foam Core	Often contains PVC or other harmful materials; releases toxic fumes.
Certain Glues/Adhesives	Materials with formaldehyde-based adhesives (e.g., some plywood) release toxic fumes.
Synthetic Leather	Often contains PVC or other harmful materials; releases toxic fumes when cut or engraved.
Polyester Films	Melts and releases harmful fumes.
Acetal (Delrin)	Releases formaldehyde gas, which is toxic.
Painted Materials	Paints may contain toxic chemicals that release harmful fumes when lasered.

- Characterization of Laser -

As all three machines have similar capabilities, we created a series of tests to standardize and characterize their focus, power, speed, rate, kerf, joint clearence and types.

Power and Speed

To be aware of cutting tolerances, a "comb" with multiple different openings ranging from -0.5 to +0.5 was created in CATIA.

We transferred it to the laser cutting program with different parameters for the letters and the outline, aiming for the letters to only be marked.

The same process was done for a comparison table of laser power vs its movement speed.

In the case of the laser cutter program, each entity was adjusted one by one with its own parameters, which was a very tedious task.

Here you can see how the combs are being cut.

Something curious about the power table, as seen in the image, is that the machine only supports a certain number of different cutting instructions. After exceeding this limit, the machine crashes and stops operating. On the other hand, the tolerance combs turned out just as expected. Thanks to these, most of the group used a tolerance of -0.2 mm for the holes.

Kerf

When a laser cutter cuts a line, it burns away material. Because a laser beam has a certain width, you end up with a part that is slightly smaller than you want, unless you account for this. The kerf of a laser is the amount of material that gets burned away

To figure this out, we cut out a series of rectangles. I tested it using both 3mm MDF and 3mm acrylic. By obtaining the number of lines, the formula becomes easy as I have that number of inner lines that count for a full kerf. By sliding all pieces to one side we create a gap that we are able to measure using a caliper. This means that the kerf can be calculated by dividing the gap by the number of cuts.

MDF 3mm 10 cuts Speed 40 mm/s Power 50%

• 3 mm/20 = .15 mm kerf

Joints

One of the most common applications of laser cutting is the creation of joints for assembling parts without the need for additional hardware like screws or glue. These are known as laser cut joints.

In the following images we show the final drawings of some joints we laser cutted. This images include the equations and variables used to design them parametrically. The original files, as well as a DXF prepared to cut them on a small scale can be found HERE.

The following designs makes use of the deformation of the material to create a joint. When designing snap joints, the deflection of the material is a critical factor to consider, as it determines how much the material can flex to allow the interlocking parts to engage or disengage. Using the formulas from the chart below which comes from the following book, you can calculate the maximum deflection (y) allowed for a given material and cross-sectional shape before it yields or breaks. These calculations take into account the modulus of elasticity (E), the moment of inertia (I), the load (P), and the geometric constants for the cross-section (such as h, b, c, etc.). Which an also help you determine how to scale the dimensions if you change the size of the joint or the material thickness, which directly impacts the deflection and the stress distribution in the snap joint.

Therefore using this formulas we arrived to the following parametric deisgns using snaps. However it's worth noting that this is all a really simplifies approach. In practice the design for a final product should pass through an iterativ process of prototyping and testing to achieve the right balance of strength and usability.

A living hinge is a thin, flexible hinge created from the same material as the two rigid pieces it connects, allowing them to pivot relative to each other. In laser cutting, a living hinge is made by making a series of closely-spaced cuts into a material, typically wood or acrylic, which allows it to bend along the line of cuts

Living hinges are widely used in product design for applications such as lids on packaging, flexible joints in toys, and movable parts in furniture, providing a combination of utility and elegant design simplicity.

So inspired by Deffered Procrastination who in their webpage calculated a way to get a parametric design of a living hinge. This is done by getting the minimum Torsional Links the thickness of the material the laser Kerf, the maximum torsional stress allowed and the minimum lenght of link. You can see the following image they provided for a visual clarification of the different part of the living hinge.

Nomenclature

• Θ = Total bend angle of the piece (Θ=θ×n)
• k_laser = Laser Kerf (m)
• l = Torsional link length (m)
• n = Number of columns of torsional links
• t = Material thickness (m)
• G = Torsional Modulus of the material (Pa)
• τ = Torsional Stress (Pa)

From this formulas we obtained the following design made in Solidworks which you can download HERE. The main parameters to change is the width of the material, the laser kerf and finally the bend angle that's needed.