Drop-in Laser Cutter Alignment Beam Works like a Charm

Every laser cutter enthusiast eventually pops the question: how on earth do I align an invisible beam that’s more-than-happy to zap my eyeballs, not to mention torch everything else in its path? We hate to admit it, but laser cutter beam alignment is no easy task. To greatly assist in this endeavor, though, some folks tend to mix a red diode laser into the path of the beam. Others temporarily fixture that diode laser directly in the beam path and then remove it once aligned.

One deviant has taken diode laser mixing to the next level! [Travis Reese] has added a servo-driven diode laser that dynamically drops into the path of the laser tube when the lid pops up, and then tilts comfortably out of the laser path when the lid closes again.

[Travis]’s beam alignmnent mechanism is Arduino powered and driven by a classic hobby servo. A firmware update moves the setpoint of the laser slightly up and down for adjustment, with about a tenth of a degree per step. While [Travis] doesn’t have all degrees of freedom exposed for alignment, this jig is more-than-sufficient for getting a matching path that’s about eyeball-accurate with the true path of the beam.

Curious? [Travis’] CAD model is up-for-grabs if you’d like to spin your own variant.

Laser alignment is tricky, but we’ve seen a few other solutions out there. For a more classic mechanism that traces the actual beam path with burn marks, have a look at [Stephen’s] method.

32 thoughts on “Drop-in Laser Cutter Alignment Beam Works like a Charm

  1. Be careful on what kind of tube you do this on. On some tubes the metal mirror mount is exposed to the internal cavity and you can arc from the anode to the mirror mount and to the servo which will fry all sorts of stuff.

    Also, you can just use a rotary solenoid, dont need any electronics with that and they are used in lots of lasers.

    Better yet get a beam combiner.

    1. The issue with some machines is that there isn’t enough room to drop in a beam combiner. I was going to add one to the laser I’m currently upgrading but don’t have the space. Good beam combiners are also kind of expensive. This guy’s method costs less than $15 if you use knock-offs and clones.

      1. Of all the machines I have seen from the little 40w units up to the larger ones there has been room for a beam combiner. You really only need maybe 1-1/2″ of space somewhere in the beampath between the tube and the second mirror. Yeah, the optic can be kind of expensive. They are somewhat reasonable on lightobject and they have a neat mount available now too.

  2. The big KW machines I used to operate just fire a pulse of IR laser at a cardboard target in a holder that goes in the beam path. It has a crosshair in the holder that blocks the beam so you can easily visualise how far off alignmemt you are.

    1. I used to work on Amada KW-range machines, and they used a similar alignment technique. They also had a red diode laser that aimed at a target on the back of the main laser’s shutter and was always on when the shutter was closed, which could help with preliminary alignment and might be a technique worth copying on a smaller laser. The trick is, of course, getting the red laser aligned with the main laser.

  3. Could you track the actual beam at a lower power/duty cycle by sticking a piece of photographic film in the path and seeing where it autodevelops? I know I can make no-development images on black and white film by setting a flashlight on top of it.

        1. Really thick thermal paper can work even on KW range machines – a regular receipt wouldn’t do; we used cardstock thermal paper. Something like this. https://www.amazon.com/White-Thermal-Transfer-Carrier-Perfed/dp/B005ED0918

          Another option if your laser doesn’t dial back very well would be to use colored acrylic. Makes a nasty garlic smell and you’ll want to blow the fumes away with a hair drier, but it can take a hit with more power.

    1. There’s no need. You put a piece of tape over one mirror, close the lid, and tap the test-fire button. Open lid, examine, adjust. Rinse wash repeat.

      Laser alignment is not a big deal in an enclosed machine.

      1. @sdfdsf, you run the risk of burning the tape adhesive into your mirror. It’s better to use something that is not touching your beam mirrors. The advantage of this improvement is also that it gives a visual indication on the work of where the laser is targeted, so it can be used to jog the machine to a starting position easily and accurately, You don’t need a laser in the system permanently just for beam alignment.You do that once and it should be mostly set.

          1. I also recommend to use some 1mm cardboard which will not burn through so easily. I usually hold it in place by tape, just over the mirror. Laser alignment tooks me about 5 minutes. Use of thermal paper (bill/receipt) is bad idea. The same with tape. You will burn through and stick fumes on mirror.

        1. Great discussion and interesting approach. About tape — careless use of alignment tape, sticking to a mirror, can definitely destroy a mirror. At our makerspace we cooked two gold/SI mirrors before this was understood. One avenue we’re investigating is a reusable detect card — we bought a Thor detect card that is sensitive to CO2 laser wavelengths. The detect card is quite sensitive. The challenge is to make alignment jigs so you can identify when the beam is hitting the middle of the mirror or lens. Tape or thermal paper might still have advantages I think for checking alignment at the four corners of the laser head travel – the detect card we bought does not persist the beam strike spot, so comparing different locations is problematic. If you align everything to dead-on center then it works well. This detect card for a CO2 laser: https://www.thorlabs.com/thorproduct.cfm?partnumber=VRC6

        2. Great discussion and interesting approach. About tape — careless use of alignment tape, sticking to a mirror, can definitely destroy a mirror. At our makerspace we cooked two gold/SI mirrors before this was understood. One avenue we’re investigating is a reusable detect card — we bought a Thor detect card that is sensitive to CO2 laser wavelengths. The detect card is quite sensitive. The challenge is to make alignment jigs so you can identify when the beam is hitting the middle of the mirror or lens. Tape or thermal paper might still have advantages I think for checking alignment at the four corners of the laser head travel – the detect card we bought does not persist the beam strike spot, so comparing different locations is problematic. If you align everything to dead-on center then it works well. This detect card for a CO2 laser: https://www.thorlabs.com/thorproduct.cfm?partnumber=VRC6

  4. So this thing is for finding the starting point of your cut right? I don’t get why Hackaday refers to other articles on beam adjustment as other approaches. that is a completely different topic. No one needs a laser that can be flipped into the beam path automatically to aling the mirrors. I mean how often do you do that? Every time you get new laser tube maybe. And then its no option to use some laser pointer which is very unlikely to be coaxial with the high power laser.

  5. Been using the tape on mirror method for 6 years on a monthly cycle with an Epilog Legend 36EXT 75 watt, but of course with power only high enough to mark the tape (why on earth would you want to burn through the tape??) We use a non-residue transfer, low tack tape so mirror cleaning is usually not necessary, but is performed as part of monthly maintenance/calibration. Due diligence pays off….

    1. Different strokes for different folks. The benefit of having a visible laser is that you can actually see it during your calibration. The benefit here is that you can make adjustments while watching the dot as opposed to adjusting the mirror, closing the cabinet, firing, opening it up, making another adjustment, closing the cabinet, firing, opening it up…..adjust once at each point and you are done.

      1. I wasn’t dogging the visible laser concept, I use that as well, but we calibrate both on our machine since they are different sources mounted separately and we use the visible laser to align items precisely (to within 1mm). My issue is with people using full power to perform tape-on-mirror calibration tests.

  6. I use the tape method on my co2 for beam alignment. BUT I also put a piece of aluminum tape down first to prevent residue from killing the mirror. This sticks to the mirror frame. Also I put a plastic disc behind the aluminum tape so it’s adhesive e does not touch the mirror. Then I just use blue 3m tape until it’s aligned. I use LaserWeb and made some macro buttons for jogging the head to the 4 positions quickly. Takes about 5 mins to align. No big deal

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