“The two happiest days in a sailor’s life are the day he buys a boat and the day he sells it.”

That also works for laser cutters. My K40 laser cutter was a lot of fun, but eventually the novelty wore off and it became a liability. I had to get rid of it. No local lab or makerspace would touch it, correctly surmising that it was a lawsuit waiting to happen. Instead, I donated it to a student interest group in my alma mater. They were thrilled to have it, and I was thrilled to be rid of it. It was a win-win for about three days until the laser cutter was kicked off-campus for being a fire hazard.

As part of the handing-over, I wrote them some instructions on how to use the machine. In case this is useful to anyone else, here it is:

Care and Feeding of a 40W Laser Cutter

This is a terrifying machine that uses a narrow beam of radiation to slice any organic material. This can hurt you and blind you PERMANENTLY. In a fraction of a second.

If you’re not at least a little afraid of what it can do, you should not operate the machine.

That said, here are some pictures.

Equipment

What’s included with the machine:

  • Machine, including the motion parts, mirrors, and laser tube.
  • Water sump (a Lowes bucket) and pump (some cheap garden thing)
  • An HVAC duct, adapter, and inline fan.
  • Some starting cutting material.
  • Some basic maintenance material (gloves, manuals, etc.)

Here’s what you need to get before using the machine:

  • Laser glasses specially designed for CO2 lasers. You want wraparound glasses with a high Optical Density (OD) for 10,600nm. Expect to pay $40 a pair or more, and ensure you buy through channels that get you a genuine set. McMaster Carr #5147T14 is $40/pair.
  • Safety interlocks. This machine doesn’t have any, and you absolutely MUST add in a way to cut power off to the laser tube (or the entire machine) as soon as any of the machine’s covers are opened.
  • A way to cut power to the machine in a hurry, like an E-stop switch.
  • Deionized water for cooling, approximately 4 Gal. (Get extra to flush the machine out with). This needs to be as non-conductive as possible to avoid arcing inside the CO2 Laser Tube. The water doesn’t need to be filtered during use.
  • A fire blanket or a CO2 extinguisher to manage fires. The latter is strongly preferred, but costs a lot more.
  • A filter for the end of the HVAC duct, if using indoors. Consider purchasing a commercial filter and fabricating an adapter.
  • Sacrificial material to cover the Z-axis surface. Perhaps some kind of spray-rubber?
  • A 3d-printed height gauge (https://www.thingiverse.com/thing:2862302). If I can find mine, I’ll add it to the equipment.
  • A computer with K40 Whisperer installed (https://www.scorchworks.com/K40whisperer/k40whisperer.html)

Optionally:

  • A shop vac with blow mode for air assist. To help improve cut quality, jam the nozzle against the front of the machine and use it to blow a layer of air over the part. It greatly improves cut quality.
  • A digital angle gauge to ensure the bed is flat.

Safety precautions

This is a dangerous, dangerous machine. If you don’t respect what it can do to you, it will hurt you. The laser will burn through gloves and skin instantly and cause damage that can’t be fixed, even with surgery. A momentary reflection can instantly bore a hole in your cornea that will forever leave a blind spot in your vision. The laser can set materials on fire, even those that are normally not flammable.

The laser beam is completely invisible. The little streak you see in the air is bits of dust catching fire as they touch the beam. The beam carries an immense amount of power in a tiny area.

You should figure out the acceptable risk profile for using such a machine and design a training program (or better still, a certification program) before allowing people to use this machine.

This is an incomplete list of rules that have kept me safe so far.

  1. ALWAYS WEAR THE DAMN GLASSES. The high-quality glasses are expensive and worth every penny.
  2. Only commission the machine after the interlocks have been added.
  3. Always be present when the machine is cutting. Material will randomly catch fire based on slight differences in material density and air currents in the machine. (I have had a 20-minute etch job catch fire after 16 minutes of uneventful cutting before.)
  4. Always start the water cooling and air extraction before running the machine.
  5. When starting a cut that you’ve never done before, keep your hand on the power kill button.
  6. Never cut in a flammable environment, especially around sawdust. That ruins your cut quality and may catch fire. (Don’t ask me how I know this.)
  7. Never cut materials with chlorine in them. It will ruin the fancy mirrors and your lungs. If in doubt, only cut the materials on the feeds and speeds list.
  8. Don’t open the machine while cutting. Duh.

When cutting, there’s eventually going to be a flare-up. It’s inevitable.

In the event of a small flare-up: remain calm. Kill power to the machine and jam a shop-vac against the front of the machine and blow it out. Or open the machine and blow it out. Try the cut again with air-assist and/or lower power. Avoid cutting paper and foams, or add a thin layer of cardboard on top of them.

In the event of a large flare-up: panic. Swing the extinguisher around wildly. Once the dust settles, claim that “it was like that when I got here.”

How to cut

  1. Pick a good material.
    1. 1/8” or 3mm thick baltic birch plywood and/or acrylic is what this machine is best at.
    2. You can also engrave basically anything organic, including sugar.
    3. Paper that is too thin might catch fire, but cardboard is fine.
    4. Place the item on the table.
  2. You don’t need any clamping because there is no cutting force.
    1. Move the table nuts around so the material is level to the machine axes
    2. Move the table vertically so the midpoint of the material is exactly 50.8mm below the lens. (Use the height gauge to check this)
  3. WEAR YOUR GOD-DAMN GLASSES.
    1. Start up the machine
    2. Start the water cooling pump and air extraction fan.
    3. Get your patterns as a .dxf file (or follow the K40 whisperer instructions for raster engraving)
  4. Start the machine up and jog it to the appropriate position. Load the cutting file and use the “move to corner” function to check that it lines up with your material.
    1. Set up the cut power and cut speed. The cut power is set on the front of the machine as percentages of 40W (here are some starting values), and the speeds are set in K-40 whisperer.
    2. Consider performing the cut in multiple passes – it improves quality. And reduces the risk of fire.
  5. WEAR YOUR GOD-DAMN GLASSES.
  6. Enable the power to the laser tube.
    1. Briefly pulse the laser using the “test” button.
    2. After the pulse is over, check the hole for cutting depth and focus.
    3. Expect to make a half-dozen test cuts to find a good configuration for your particular material. Write this down somewhere – it will save you a lot of annoyance.
  7. Hit the start button.
    1. Keep the power kill handy.
    2. Keep your extinguisher and/or blanket handy.
    3. Pay attention.
    4. Don’t wander off.
  8. Get your part
    1. Kill the power to the laser tube before opening the machine.
    2. Check that the cut is clean through the material – you can just re-run the same program to finish the cut if necessary, but only if you haven’t moved the material at all.

Forcing more air through the system will remove the gases from the cut area, and allow more power from the beam to be delivered to the cut. This is called an “air assist”, and the cheapest way to do that is to push the blower end of a shopvac to the hole in the front of the machine. Use that to blow air over the surface of the part.