# Main Laser Page

The purpose of this page is to provide laser cutter users with an understanding of how a laser cutter works, how to cut and engrave on the laser cutter, the limitations of the laser cutter, and demonstrative parts. The MIT MakerWorkshop currently has an Epilog Fusion 40 and a Universal VLS 3.50. There are many sources of inspiration for what may be done with these laser cutters, including the Epilog sample photos page, the Trotec applications page, the Universal Laser Systems Laser Markets page, and Instructables. The Overall Laser Cutter Procedure, Universal Laser Refresher, and Epilog Refresher are linked.
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# Laser Physics and History

### What is a laser and how does it work? (citations needed)

Laser is an acronym that stands for Light Amplification by Stimulated Emission of Radiation. Here's a video of how it works. There are several ideas that are key to the implementation of a laser: quantized energy levels, light amplification, and optical pumping. Max Planck proposed the idea that electromagnetic energy is emitted in quantized form in 1900 with his famous equation: E = hν, where E represents the energy of a photon, h is Planck's constant, and ν is the frequency of the photon. Then Einstein presented the idea of light amplification (the photoelectric effect) in 1917. When an incident photon of the right frequency hits an atom at an excited energy level, then the atom returns to its ground state and the number of photons doubles. Optical pumping is needed to excite the ground state atom to continue the process of light amplification. Alfred Kastler first proposed the idea of optical pumping in 1950. The first working laser was developed in 1960 by Theodore Maiman.

### Laser Construction

The lasers that we use for laser cutting use an electric discharge pump and CO2 as the laser medium.

### Why use lasers for manufacturing?

Lasers have a high areal power density which provides enough local heat to cause a phase change in certain materials. For example, a 100W light bulb can be focused to a spot diameter of 0.01m (areal power density is 1.3 MW/m2), while a 100W laser can be focused to a spot diameter of 0.0015 m (areal power density: 5700 MW/m2).

### How are lasers used in manufacturing?

The laser beam comes from the source and bounces of several mirrors until it goes through a focusing lens.

The depth of cut through a material is given by the following equation, where z is the cut depth, P is the laser power, v is the laser speed, d is the beam spot diameter,a is the material absorptivity, ρ is the material density, cp is the specific heat of the material Tv is the vaporization temperature, T is the ambient temperature, and Lf is the latent heat of fusion. The constant in front comes from assuming that the laser beam has a Gaussian distribution (i.e. it is not a uniform heat source.)

# Materials

Laser cutters can cut a wide variety of materials including plastic, wood, metal, and ceramics. However, the laser cutters in MakerWorks are not powerful enough to cut metal or ceramics; they can only engrave them. Also, there are many plastics that may not be cut in MakerWorks because they release fumes that are toxic and/or flammable. A full list of materials that are and are not allowed is contained in another page.

### Plastic

Many plastics are dangerous to cut, either to the machine or to the user. Thus, the policy for cutting plastics is that there will be no "mystery materials" to be cut. For example, just because the plastic piece you found in a scrap pile looks like acrylic, doesn't mean that it is acrylic. There are ways to identify plastics by burning them, but these destructive methods will not be employed in MakerWorks.

### Wood

Wood may be cut or engraved on the laser cutter. There is a danger of the wood catching fire if the power settings are too high or the speed it too low. Also, in particularly long wood cutting/engraving jobs the soot created may coat the nozzle or the lens and a fire may be created if the laser burns the soot. The job may be paused to clean the nozzle/lens.

### Metal

The MakerWorks laser cutters is not powerful enough to cut through metal, but it can engrave under special circumstances. Although the laser is not powerful to ablate the material directly, it can ablate away a coating, such as an anodized layer or paint.

### Glass

The MakerWorks laser cutters are not powerful enough to cut glass, but they may be engraved. The glass engraving process is not the same as ablating away material. The heat from the laser causes crazing at the surface of the glass. The material engraving techniques are described in the Epilog laser manual. The fracturing of the glass produces a frosted appearance, but it may cause roughness or chipping depending on the type of glass being engraved. The frosted appearance is desired, but the roughness and chipping are not. The composition and quality of glass varies widely, thus it is always best to experiment with an unfamiliar glass source. Generally, flat glass has a consistent hardness, while bottles tend to have soft and hard spots that will cause the engraved area to appear lightly frosted in one area and heavily frosted in another. Engraving at medium speed and high power will somewhat compensate for this, as will two or more engraving passes.

To produce a smooth frosted finish, follow this procedure (adapted from the Epilog manual):

• Apply a thin coat of liquid dish soap over the area to be engraved using your finger or a paper towel
• Cut a piece of newspaper or paper towel a little larger than the area to be engraved. Completely soak the paper with water then wring out the excess water.
• Apply the paper to the glass and smooth out the paper so that there are no wrinkles.
• Place the glass into the engraver and laser through the paper while it is still wet.
• Remove the glass, discard the remaining paper, and clean the glass.
• If necessary, gently polish the glass with a ScotchBrite pad.

Be especially careful when laser engraving leaded crystal. The lead in the crystal expands at a different rate than the crystal which may cause cracking or breakage. Using a lower power setting may help, but it is advisable to have a spare piece in case of breakage.

### NEVER CUT THESE MATERIALS

This section is adapted from the ATX Hackerspace list. There may be more materials beyond this list that should not be cut. In general, check the material safety data sheet (MSDS) for the material and ensure that the material is not flammable, explosive, or produces toxic byproducts when laser cut.

Material DANGER! Cause/Consequence
PVC (Poly Vinyl Chloride) / vinyl / pleather / artificial leather Emits pure chlorine gas when cut! Don't ever cut this material as it will ruin the optics, cause the metal of the machine to corrode, and ruin the motion control system.
Polycarbonate/Lexan Fire and toxic flammable gas. The window of the laser cutter is made of Polycarbonate because polycarbonate strongly absorbs infrared radiation! This is the frequency of light the laser cutter uses to cut materials, so it is very ineffective at cutting polycarbonate. Polycarbonate is a poor choice for laser cutting.
ABS Emits cyanide gas and tends to melt ABS does not cut well in a laser cutter. It tends to melt rather than vaporize, and has a higher chance of catching on fire and leaving behind melted gooey deposits on the vector cutting grid. It also does not engrave well (again, tends to melt).
HDPE/milk bottle plastic Catches fire and melts It melts. It gets gooey. Don't use it.
PolyStyrene Foam Catches fire It catches fire, it melts, and only thin pieces cut. This is the #1 material that causes laser fires!!!
PolyPropylene Foam Catches fire Like PolyStyrene, it melts, catches fire, and the melted drops continue to burn and turn into rock-hard drips and pebbles.
Fiberglass Emits fumes It's a mix of two materials that cant' be cut. Glass (etch, no cut) and epoxy resin (fumes)
Coated Carbon Fiber Emits noxious fumes A mix of two materials. Thin carbon fiber mat can be cut, with some fraying - but not when coated.

### Safe Materials

This section is adapted from the ATX Hackerspace list.

#### Cutting

Material Max thickness Notes WARNINGS!
Many woods 1/4" Avoid oily/resinous woods Be very careful about cutting oily woods, or very resinous woods as they also may catch fire.
Plywood/Composite woods 1/4" These contain glue, and may not laser cut as well as solid wood.
MDF/Engineered woods 1/4" These are okay to use but may experience a higher amount of charring when cut.
Paper, card stock thin Cuts very well on the laser cutter, and also very quickly.
Cork 1/4" Cuts nicely, but the quality of the cut depends on the thickness and quality of the cork. Engineered cork has a lot of glue in it, and may not cut as well. Avoid thicker cork.
Acrylic / Lucite / Plexiglas / PMMA 1/2" Cuts extremely well leaving a beautifully polished edge.
Delrin (POM) thin Delrin comes in a number of shore strengths (hardness) and the harder Delrin tends to work better. Great for gears!
Kapton tape (Polyimide) 1/16" Works well, in thin sheets and strips like tape.
Mylar 1/16" Works well if it's thin. Thick mylar has a tendency to warp, bubble, and curl Gold coated mylar will not work.
Depron foam 1/4" Used a lot for hobby, RC aircraft, architectural models, and toys. 1/4" cuts nicely, with a smooth edge. Must be constantly monitored.
Cloth / felt / hemp / cotton They all cut well. Not plastic coated or impregnated cloth!
Leather / Suede 1/8" Leather is very hard to cut, but can be if it's thinner than a belt (call it 1/8"). Our "Advanced" laser training class covers this. Real leather only! Not 'pleather' or other imitations!
Magnetic Sheet Cuts beautifully
NON-CHLORINE-containing rubber Fine for cutting. Beware chlorine-containing rubber!
Carbon fiber mats/weave
that has not had epoxy applied
Can be cut, very slowly. You must not cut carbon fiber that has been coated!!

#### Etching

All the above "cuttable" materials can be etched, in some cases very deeply.

Material Notes WARNINGS!
Glass Green seems to work best...looks sandblasted.
Ceramic tile
Anodized aluminum Vaporizes the anodization away.
Painted/coated metals Vaporizes the paint away.
Stone, Marble, Granite, Soapstone, Onyx. Gets a white "textured" look when etched. 100% power, 50% speed or less works well for etching.

# Pre-Processing: Graphics Generation

The laser cutter runs on a printer driver, so sending an image to the laser cutter is as easy as printing something out on a sheet of paper. That is, most graphics programs will suffice for laser cutting. Preferable graphics programs are vector graphics programs including Adobe Illustrator, CorelDraw, or Inkscape.

### Importing DXFs

There are a couple of options for creating appropriate Illustrator files from SolidWorks.

#### From a drawing

From a SolidWorks drawing, choose Save As... -> Adobe Illustrator Files (.ai). This will create an Illustrator file at the DOCUMENT SCALE, so set the sheet to 1:1 in SolidWorks. Individual parts on a sheet will be created as Compound Paths. If you want to modify or clean up any paths, right click on the part and choose Release Compound Paths. It is desirable to reduce the number of points used to describe the path by selecting the objects then going to Object -> Path -> Simplify. Check the Preview button to see what Illustrator is doing.

#### From a SolidWorks part

From a SolidWorks part, choose Save As... -> .dxf. Under Export, choose Faces/loops/edges and select the 2D face that you want to export. Confirm that tis is the correct view on the next dialog box and hit Save. In Illustrator, open the file. In the dialog box, change the pulldown to the units the file was made in and make sure it says "1 Unit(s) = 1 [chosen unit]." Click OK. Simplifying the path may be done as in the "From a drawing" section, but this method tends to not require points simplified.

# Vector Cutting

Vector cutting is when the laser cuts along the vector lines of the image. The vector lines need to be sufficiently thin for the laser cutter to recognize them as vectors for cutting. In CorelDraw, the lines need to have a weight of "Hairline", and in Illustrator the lines need to be $\leq$0.1pt.

### Vector sorting and optimization

First you should simplify the vector cutting path as much as possible (especially for splines). This may be done by going to Object -> Path -> Simplify in Adobe Illustrator.

Next the vectors should be sorted. The default setting for the Epilog disables vector sorting in the Print dialog menu. Thus, it cuts the vectors as they are ordered in the layers menu (the order that they were placed in Illustrator). This is often undesirable, since the laser wastes a significant amount of time traveling between cuts. What is nice about that though is that it is less likely to cause a fire or warping of the part. The way to fix that is to go to the Epilog Job Manager and go to Vector Sorting. Vector Sorting has three options: none (default), Inside-Out, and Optimize. Inside-Out makes sure that all of the parts that are supposed to be "holes" are cut first, then the outer perimeters are cut. Optimize cuts the vectors such that it minimizes the time overall.

Color Mapping allows the most control over the order of the vectors, since the vectors will be cut in the order of the colors listed.

### Color Mapping

Color Mapping allows the most control over the order of the vectors. Color Mapping applies different settings to different colors in your image. This is enabled by default in the Universal laser cutter, and it is optional for the Epilog. This may be used to apply different speed and power settings for cutting different materials or for vector scoring. Vector scoring involves not cutting all the way through the part to make sharp outlines for images. For the Epilog, the focus levels may also be changed for cutting on a multilevel workpiece. The vectors will be cut in the order listed. The colors need to be mapped to the exact same RGB values as the colors in the image.

### Kerf Compensation

The laser cutter does not compensate for the kerf of the laser. That is, the laser cuts on the middle of the line. This is problematic for pieces that have tight tolerances, especially press fits. The kerf must be compensated manually, in SolidWorks, OMAX Layout, or Illustrator.

# Engraving

Laser engraving is the process of ablating away the top layer of material (not cutting all the way through) to etch a picture on the top surface. This may be useful for several things including labels, graphic transfers, rubber stamps and notary seals. Laser engraving rasters the image on the surface.

### Parameter Selection

#### DPI

DPI (dots per inch) represents the resolution of the engraved job. Most users try to apply the highest resolution possible for engraving, but this is not necessarily a good idea in terms of time and quality. For example, going from 600 DPI to 1200 DPI literally takes twice as long and applies four times as much heat for a minute visual improvement. The additional heat may cause wood to scorch or plastic to warp. However, having a resolution that is too low is often not desirable either; using 150 or 75 DPI is for draft quality engravings to test aspects such as positioning.

#### Dithering

Dithering in the context of laser cutting is a matter of how the laser dots are clustered together to produce a high quality image. Standard looks like a comic book or a newspaper, Brighten will make the whole image look brighter (works especially well on wood), Low Res will actively try to smooth out a low resolution image, Floyd-Steinberg, Jarvis, and Stucki all look pretty much the same and they are especially suited for photo engraving.

### Basic Engraving

The "basic" engraving engraves with a constant power. It takes a grayscale image and clusters the laser dots closer together in the darker areas of the image and spaces the dots further apart for the lighter areas of the image.

### Rotary Engraving

The Universal laser cutter has a Rotary Attachment for engraving rotationally symmetric objects like bottles, champagne glasses, rolling pins, etc. Using the rotary attachment involves fixturing, setting up the software, and engraving.

#### Fixturing

The rotary attachment has two parts to the fixturing: a motorized end and a free-spinning end. The free-spinning end may be axially adjusted by sliding it to the correct position and locking it in place with a lever. Each end has a shaft where the various fixtures may be attached via set screws. There are several possible combinations for fixturing and the best option depends on the application. Engraving fragile objects (glass bottles for example) should use the fixturing cones with the rubber attached. Engraving cylindrical objects like wood or metal should involve the 3-jaw chuck on the motorized end and the delrin live center on the other end. All of the fixturing options are attached via set screws so they may easily be replaced. The rotary attachment may be inserted into the laser cutter once the proper fixturing is attached. To insert the rotary attachment into the laser cutter, lower the laser bed all the way, remove the laser bed and set it in the laser cabinet on the laser attachments shelf. Then insert the rotary attachment ensuring that the female connector on the rotary attachment engages with the male connector on the laser bed. Also, care must be taken to ensure the laser head does not run into the fixture. This may be done by sufficiently lowering the speed or by using spacers with the fixturing.

#### Software

First, measure the diameter of the piece you are engraving with the calipers that are in the laser cabinet drawer. Write down the diameter. The diameter is important to get the correct "Y-axis" speed since the rotary attachment controls angle, not position. Next, position the laser to the left- and right-most extremes of where you want to engrave on the workpiece and right down their respective X-coordinates. Then, rotate the material by hand until the position you want to be the center of your graphic is facing directly up. The rotary attachment does not have a home location in the rotation axis so the top most partof the materialis always the center of the graphic when printing using the materials driver tab or the center of the page when printing using the manual driver tab.

Now that the graphic placement has been determined, the image needs to be modified accordingly to ensure that it is the correct size and at the correct position. The page size (artboard size in Illustrator) needs to be 24" wide in the X-direction (i.e. the full width of the laser cutter) and the height in the Y-direction needs to be the circumference of the material. The position needs to be centered vertically on the page, within the X-axis limits recorded earlier, and rotated 90° In Illustrator, go to File -> Print, then choose the Universal Laser Print Preset, then click Setup in the lower right, then choose the Universal laser cutter, then click Preferences. In the ULS printer driver properties dialog, press the Engraving Field sub-tab within the Manual Control tab. Press the "Max Size" button. Check the "Enable" selection box in the Rotary section to enable rotary mode. Type in the diameter of the material measured earlier. The height dimension of the engraving field becomes the circumference of the material. Make a note of this engraving field size and exit the printer driver properties dialog. Make the page size equal to the new engraving field size from the print driver dialog. Center the graphic vertically and position it horizontally within the X-axis limits.

Finally, print the file and check to make sure rotary mode is still enabled and the correct diameter is still entered in the printer driver dialog.

#### Engraving

Select the appropriate speed and power settings before printing the job. The speed setting may need to be lowered to ensure that the laser head does not run into the fixturing. To keep the same depth, the power needs to be reduced accordingly, i.e. to engrave to the same depth, the power to speed ratio needs to remain constant.

### Marking

Marking is different from engraving because rather than ablating away the material, it uses the heat from the laser to change the color a chemical coating on the surface of the material. This is especially useful for engraving on metal. One example is AlumaMark, which is aluminum that is covered with a special coating that turns black when engraved. It comes in a variety of colors. Another example of marking is CerMark, which is a coating that is applied to a metal. The CerMark coating turns black and adheres to the metal when engraved and the excess may be washed off.

# Assembly

Acrylic may be joined using acrylic glue, which is actually a solvent for acrylic. This fuses the acrylic together rather than just placing glue in between.

### Bolted Joints

Bolted joints may be incorporated into the design using so-called T-nuts.

### Snap-Fits

Snap fits involve the use of flexures to snap a piece in place, like on a seat belt buckle. A list of digital joints is shown here

### Press-Fits

Press-fits require a difference of about 0.003". This is bigger than the kerf width of the laser, so kerf compensation is essential.

# Post Processing

### Bending

Plastic may be bent by locally raising the temperature beyond the glass transition temperature via a strip heater or a heat gun.

### Deburring

The edges of laser cut parts may be deburred with a deburring tool or an edge scraper.

### Plastic Finishing

Scratches or other marks may be removed by using a plastic finishing kit.

### Sanding

Sanding is used to gradually alter the surface finish, usually in wood, but in plastics as well.

### Wood Finishing

Wood is an anisotropic, porous material that will absorb moisture from the air. The humidity will cause the wood to warp in various ways. Adding a finish creates a mostly impermeable membrane that retards the warping process. Thus, it is often an essential aspect of woodworking. Here are some recommended wood finishes...

### Painting using stencils

Laser cutters may be used to cut stencils. The stencils may be used by applying spray-paint. The stencils should not have lines that are too thin as the paint may bleed around the lines. These stencils may be created by using the image trace feature in Illustrator.

### Color Fill

Color fill is a paint that may fill an engraved surface. The paint fills the cavity that was ablated away and the excess is wiped away. This works especially well with engraving a mirrored image on a clear material like acrylic.