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Laser Cutting Class
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Lesson 3: Prepping and Laser Cutting
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In this lesson, we'll learn how to prep material and setup the machine to get the best results. We'll learn how to prevent soot stains, calibrate for precise cutting, and clean up finished parts.

For this class, we're using plywood, which is a great material for laser cutting. It cuts evenly, the edges stay square (which can be a problem with other materials like acrylic), it's easy to stain, sand, paint, and finish in lots of different ways.

The 120 Watt Epilog laser we're using can cut plywood as thick as 3/8", but at that thickness, it takes a lot of power and slow speeds, so there's more risk of small fires. Although usually not a serious safety hazard, these little blazes will ruin your parts.

1/4" (6mm) plywood is pretty much the thickest I use on these machines. 1/8" (3mm) plywood also works well and cuts faster since it's half as thick.


Masking: Soot Stain Prevention

The laser cutter cuts by burning- it's oxidizing flammable material with a very focused beam. This oxidation produces soot which (especially with plywood) will stick to the material's surface. It can be very difficult to remove, so I recommend masking the material whenever possible.

The underside of the material being cut tends to get the worst of the soot because it's where the soot blows out. The metal honeycomb of the bed also gets imprinted into the underside of the material as a result, so it's really important to mask the underside. Some soot will always blow around on top of the material as well, so I always mask the top as well.

Generic painter's masking tape will work just fine, but I use the 6" wide painter's tape because it gets the job done much faster.

Apply it with a card from your wallet as a spatula to make sure it's completely stuck to the surface without any bubbles or creases.


Focusing

Focusing is crucial for getting a precise cut. If the laser nozzle is too far or too close to the material, the beam will be wider than it needs to be. This causes the kerf to be wider than .002" (.05mm) and will cause interlocking parts to be too loose for a proper fit.

Focus also affects the power of the beam. Think of a magnifying glass in the sun– if you move it too close to the surface, it's not hot enough to burn. If you move it too far, you get the same problem.

There are two ways to focus on the Epilog Legend 36 EXT laser cutter:

AUTOFOCUS

This model has an autofocus feature that works with a spring-loaded plunger.

  1. Press the FOCUS button on the keypad- this will move the laser head to the upper right corner of the bed.
  2. Press GO and the bed to automatically move up until the plunger is depressed.

At our shop, we don't use this method. When you have a lot of users sharing machines they tend to get beat up. These plungers are delicate and likely to get damaged. The bed will raise until the plunger is depressed, so if the plunger is damaged the bed will just keep going- this can damage the laser head! For this reason, it's best to use method 2...

MANUAL FOCUS

With this method, you manually move the bed up and down until it's at the proper height in relation to the laser head. Here's how it's done:

  1. Press FOCUS to automatically move the laser head to the upper left corner of the bed OR press X/Y OFF to disengage the motors, then manually move the laser head to the desired position over the material. This can be useful if your material isn't rectangular and doesn't cover the upper left corner of the bed.
  2. Place the Focus Gauge on the laser head. It's magnetic and has holes for posts on the laser head, so it snaps into place.
  3. Press the UP and DOWN arrows to move the bed up and down. When the gauge is touching the material, the laser is focused.
  4. Remove the focus gauge and press RESET and you're ready to start cutting.


Cutting

In the previous lesson, we learned how to input cut / etch settings and send the job to the laser cutter. If everything was done properly, the job will appear in the job list on the display on the laser cutter's keypad. To run the job, use the arrows to cycle through and select it (if more than one has been sent) and press GO to run the job.

Remember to check and make sure the ventilation is on! This can be easy to miss when you're in the zone. In our shop it's a big button on the wall with a green light.

With the proper settings, 1/8" (3mm) plywood cuts with no problem. 20% is pretty fast, so the box should be complete in about 3-4 minutes. The glass door must remain closed for safety, and if you open it while the file is running the laser will turn off while the head continues to move.

Remember, safety first! If the laser is running with too much power and not enough speed, materials tend to catch fire. Quick flare-ups aren't usually a safety hazard, but sometimes they turn into full-blown fires. If you see one, stop the job, open the door, and put the fire out. Usually, this can be done with a spray bottle full of tap water, but you should always have a fire extinguisher handy and know how to use it.


Cleaning Parts

With properly masked panels, the soot stains the masking tape instead of the face of the material. The tape can be peeled off easily and will save lots of time cleaning and sanding.

Cutting without masking leaves soot stains.

Masking tape protects material faces from soot

With plywood, the edges will always have a bit of soot on them. A good trick for cleaning them up is to use some shop-grade hand scrub like Fast Orange and an electric toothbrush. The pumice in the soap helps get the soot off of the edges, and the toothbrush helps you reach the tight crevices in a piece like this.

Leave the tape on the faces of the parts to minimize the amount of water that gets on the plywood. A quick rinse in the sink and about 30 minutes of drying out, and the parts are ready for assembly.


Assembly

Plywood is nothing special- all it takes it a little wood glue to assemble the box. I use masking tape to keep the sides square while the glue cures.

I leave the bottom panel unglued so that it press-fits into place, and my tissue box is done!

What did you make for your first laser cut project?

{
    "id": "quiz-1",
    "question": "Why is manual focusing better than automatic focusing?",
    "answers": [
        {
            "title": "Because it's more accurate.",
            "correct": false
        },
        {
            "title": "Because the focusing parts might be damaged.",
            "correct": true
        }
    ],
    "correctNotice": "That's right– if the focusing parts are damaged, the autofocus operation will cause the bed to keep moving. This can make it crash into the laser arm!",
    "incorrectNotice": "Nope!"
}
{
    "id": "quiz-1",
    "question": "What will happen if cut lines aren't set to .01 instead of .001?",
    "answers": [
        {
            "title": "Nothing.",
            "correct": true
        },
        {
            "title": "The laser will cut the lines at 1/10 the power specified.",
            "correct": false
        }
    ],
    "correctNotice": "You got it!",
    "incorrectNotice": "Nope! The lines will not cut at all."
}
{
    "id": "quiz-1",
    "question": "What will happen if a job is run with the laser out of focus?",
    "answers": [
        {
            "title": "The kerf width will be bigger. If it's way out of focus it might not cut at all.",
            "correct": true
        },
        {
            "title": "The job won't run at all.",
            "correct": false
        }
    ],
    "correctNotice": "That's right! focus affects both cutting power and kerf width.",
    "incorrectNotice": "Nope!"
}

CLASS PROJECT

Share a photo of your finished project with the class!

Nice work! You've completed the class project