Laser Cutting at CABE
Basics of Laser Cutting
The laser cutters at Jefferson University are sophisticated CNC machines that use focused infrared lasers to vaporize materials based on your instructions. There are three operations that this vaporization can be described as: raster engraving, vector cutting, and third that shares aspects of the previous called vector scoring.
You can see an example of these below:
You can see an image of the underlying design file here:
In this operation, the laser beam travels over the entire area of your shape. Raster engraving is a marking operation used for decoration or information. The laser will quickly vaporize a thin debossing into the top surface of the material. The depth of this debossing can be adjusted roughly with different speeds. This operation requires the area to be filled with pure black color. If your design has fuzzy edges, or gray areas, those will be interpreted as a halftone in the laser software. This way it is possible to engrave grayscale images. Raster engraving is useful for marking text onto a design. It can also expose a different color in some specially designed layered materials. The time required for raster engraving is dependent on the overall area the laser must travel to reach your black-filled designs.
Raster engraving is the only operation that can be used with bitmap images such as jpegs, pngs, gifs, or bmps. All color will be reduced to a black and white halftone in the software, so make your own grayscale first.
Vector cutting is an operation that can cut your material all the way through. This operation is used for making specific shapes and cutting material to size. Here the laser slowly travels along a thin line in your design while vaporizing all the material along its path. This operation requires more than an image. We need to program the laser with vector lines. If you use CAD or Illustrator you are familiar with vectors. Instead of pixels describing an image, vectors are mathematical formulas that describe the shape of a line. This makes them perfectly scalable and allows us to program a robot to carefully follow such lines. For vector cutting your lines need to be very distinct from any raster engraving art. Vector cutting lines must be pure red in color and include a stroke that is as thin as possible; 0.1 pt will work in most cases. The laser software is programmed to recognize these lines and the laser will follow them exactly. Vector cutting is like cutting with a saw in that some material will be removed during the process. This is called the kerf and for lasers generally measures .005” but will vary based on your material thickness. If you need exact cuts that account for kerf, try a test cut with your material first and measure your results. In the sample above there are horizontal pylons connecting the counters in the middle of some letters. Keep in mind that vector cutting can completely separate your material into pieces, and some of those pieces (like the counter inside an "O") you may want to retain. This operation adds time to your job based on the length of all your cut paths.
This operation is halfway between raster engraving and vector scoring. Like raster engraving, it is used to mark your material, but it is programmed like vector scoring. In this operation, the laser travels along the vector line you designed, but does so quickly just removing a small amount of material from the surface. To design for this operation, use a thin line of 0.1 pt or less but with a pure blue stroke color. This color will differentiate your vector scoring designs in the laser software. Vector scoring is a faster way to make marks on your material that are less dense than raster engraving. A good example could be a grid of thin boxes denoting windows on a facade or building footprints. Like vector cutting, this operation adds time to your job based on the length of all your vector scoring paths.
Preparing Your File
Any CAD or vector drawing program can generate laser cutting files. Keep in mind the 3 types of operations discussed above and use them to design your file:
Black filled objects
Vector or Bitmap
Blue 0.1pt stroke paths
Red 0.1 pt stroke paths
You must not include any other lines in your file that are not described above. Lines of any greater thickness or other color will be interpreted as shapes for raster engraving. For example, a simple 1pt green box around your design will increase your laser time by over an hour as the laser travels over the entire area of the box to engrave the green box as a light raster engrave.
Size & Scale
You must work in full 1:1 scale for your design. Your dimensions in your design file must represent real dimension of your laser cut objects.
The laser has a max sheet size of 18" x 32". Your material can be no larger than this. If it is even an eighth of an inch over, it will not sit flat on the cutting bed and the laser beam will not be in focus. You can cut any sheet material to size in the Weber shop.
The max thickness of your material is constrained by the power of the laser. We can cut up to ½" material in most cases. For thicker materials, you should plan a test cut first. Always test a laser cut with a circle, as they are harder for the machine to cut than straight lines.
The majority of laser cutting is done with three materials:
- Wood, plywood
- Paper, cardboard, chipboard
- Acrylic (aka PMMA, Plexiglass)
The list of materials we can't cut is much longer:
- Anything containing chlorine
- Polycarbonate (aka Lexan)
- PVC (aka vinyl)
- Styrene, polystyrene
- Foam Core (the core is polystyrene)
There are many other materials that may be cut including most “natural” materials, but these should be approved by the Resource Manager Chris Thompson before laser cutting.
We prefer to accept PDFs for laser cutting. PDFs can carry accurate vectors and bitmaps and maintain scale well. They are also smaller files which puts less pressure on our laser computers. If your PDF is drawn poorly, the laser operators will allow you to modify your design and return with a decent PDF. Your page size should match your material size, also being no larger than 18" x 32".
AutoCAD is the first CAD program most PhilaU CABE students are taught. You can use the following AutoCAD DWG template to lay out your design for cutting. Please copy your design geometry into this document for laser preparation.
This file has three layers that correspond to the three laser operations. You can use these layers to color your designs, or style them in a different fashion, as long as it matches the requirements described above 100%. There is no negotiating with the laser software. If your line is too thick, it will not cut.
While you may bring your DWG or DXF files to the laser lab to cut, we insist you try to export a PDF first for the overall efficiency of the laser cutting process.
It is easy to generate laser files in Adobe Illustrator and graphic designers may feel more comfortable generating complex designs in this vector software. Illustrator also handles text far better than any CAD program. The same color and line rules apply. You should set your artboard size to match your material size. Please “outline” your text to avoid font problems. Laser operators will not bother with installing fonts. You must also work in the RGB colorspace. You can change this in the file menu. Do this first before drawing or adding anything to your document. You may need to switch the color palette to show RGB values. For reference the black is 0 red, 0 blue, and 0 green. For red and blue, those color sliders must be set to the max of 255. You can easily save PDFs from Illustrator. Checking “Preserve Illustrator Editing Capabilities” during saving will not affect the PDF output, but will help your revisions.
Any CAD program can save DXFs and you can export these as PDFs from AutoCAD. Any other vector program, such as free Inkscape, can print PDFs though the OS. These files will retain all the correct color and line weights that you chose during your setup.
You can bring your file on a USB drive, your material, and your ID with PhilaU Declining Balance funds available. The laser cutters are in room 131 of the SEED center. Review the Laser Lab hours on the combined CABE shop schedule:
You will be asked to fill out an order form with details about your job, materials, and contact info. The laser time is charged at the rate of $0.20 per minute.
Laser jobs are cut in the order they are received, but the laser operators may put longer jobs later in the queue to maximize lab throughput. Please ask Chris Thompson or a lab monitor for tips on reducing overall time for your laser job. Laser operators may also turn down jobs that are inappropriate for laser cutting. For example, the laser is not the appropriate tool for cutting large quantities of identical squares. You can receive training in Weber shop that will allow you to cut 200 squares of any material in 15 minutes, much faster than a laser cutter.
When your laser job is complete you will receive an email or phone call alerting you to pick up and pay for your job.