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2x:aligning_the_optics

Laser Optics Alignment

Alignment should only be done by a competent person who fully understands all the safety issues related to aligning lasers. Below is a partial list of things to remember when doing this.

  • Everyone within range of the beam should be wearing safety glasses rated for this procedure.
  • A fire extinguisher should be handy to put out any fires. The beam can travel very far with enough power to instantly ignite anything it strikes.
  • Stay clear of all tube electrodes by at least 4 inches.

Overview

The first thing to understand is this process is not just about aiming the beam from mirror to mirror. You must start with a square and level XY assembly. There is no way to align a system that is not square and level. When the beam reflects off a mirror it must hit the exact same location on the next mirror regardless of where it is in it's travel. It does not matter where it strikes the mirror as long as it hits the same place all the time. Therefore the difficult alignments are only related to the moving mirrors. It is is best to start at the tube and work your way towards the final mirror and lens.

You will be using the laser to make marks on a target during this process. Many people use thermal fax or calculator paper because it marks with the minimum about on beam power. I often use a small block of wood. It takes more power, but it is a little more stable and less likely to move around. You will fire the lasers many dozens of times, so have a lot of material ready.

  • Disconnect power from the machine. You don't want any chance of the beam firing while you are making the initial adjustments. There is danger from the beam and high voltage.
  • Square up the gantry. Start by making sure the gantry is square with the Y axis. The 2.x Y axis is driven by 2 belts. Therefore, you can adjust the squareness by loosening one of the pulleys slightly and rotating it on the drive shaft. Get it as close as possible. You can do a slight bit of tweaking later, but not much.
  • Center all the mirrors. Use the adjustment screws to move the mirrors away from the mounts about 1-2mm. This will allow some back off adjustment later. The mirrors all have some adjust in the mounting. Using common reference points try to adjust the centers of the mirrors to a common plane. I like to use the edge of the extrusion.
  • Aim the tube. Try to do your best at getting the tube level and pointing directly at the center of the first mirror. Since this mirror does not move the beam can have a little angle to it without causing any problems. Never touch the tube when the machine is plugged in.
  • Align first mirror. Move the gantry as far back as possible. Place a target in front of the next mirror. Keep firing and adjusting the mirror until it looks like it would hit the center of the next mirror. Once you get pretty close you need to move the gantry to the other end of travel with the target held firmly in place. Make another mark. There will now be two marks on the target. You want there to only be one. Since there are two spots, it means that the beam is at an angle. If you draw a line between the two spots, the desired spot is probably somewhere on that line outside the two spots on the side side you marked closest to the mirror. The distance would be proportional to the where on the gantry you fired the two spots. In reality the mirror does not “gimbal” about the beam and displaces when you move it, so you can only guess at the next location.

In this image 'A' was the spot made near the mirror, 'B' was made far away from the mirror and 'C' would be a decent guess for the next try

This image shows what is going on. The orange triangles are mirrors and the blue rectangles represent the target. As you can see an angled beam will create spots off to one side of the ideal beam.

  • Align Second Mirror
  • Final Mirror. The final mirror is the mirror that reflects down and through the lens. This is not normally adjustable, but it is very important that is is square with the previous mirror. This mirror can often rotate along a vertical axis. If it is rotated off square with the previous mirror, it may still work, but the beam will angle slightly on it's way down. Your cuts will have a slight angle to them.

2x/aligning_the_optics.txt · Last modified: 2011/08/26 11:36 by bdring