Autofocus glitch leads to unfocused engraving on glossy surfaces

Hello all,

I am having an issue printing on (visible light) reflective surfaces. During the autofocus stage of the pre-printing process (autofocus->route calculation->ready to print) on a glossy surface, such as kapton tape or glass, there is a glitch that leads to:

  1. Depending where the part to be printed is, the printing area gets zoomed out afterwards, while the printing design remains the same. In short, it is like the design remained steady and the printed area shrunk.
  2. If you press the button and move on with the printing after this glitch, the printing results will be highly unstable (defocused?). It can print elsewhere, or keep the location but have huge differences in printing quality compared to when the glitch is not present.

This is giving me a huge headache. I noticed that the position of the printing material inside GlowForge will affect if this glitch will or will not be present. It seems like the focusing laser is being reflected into the camera, but this is just my guess. In fact, glass or Kapton should not reflect IR light. However, if I place the reflective surface right below the GF camera, I have a considerably smaller chance of glitching. My guess is that during the focusing process, the laser head is blocking the focusing laser light path to the camera.

Could any one help me finding a permanent solution to this? A technical feedback from staff would be great. I am sure this is not the first time this happens.

By the way, I use my equipment in very specific academic setups, and cannot replace my working material for proofgrade ones. Nevertheless, they should be laser safe (no corrosive/oxidative gases nor laser reflecting). They are all quite smaller than 1/2".

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The autofocus mechanism uses a separate small red laser diode mounted at an angle, not the large infrared CO2 laser tube used for cutting/engraving. (There’s a small camera on the head that takes a closeup photo of the surface to see where the red dot falls.)

Your best bet is to put a small square of masking tape somewhere on the item and use the Set Focus command to make the Glowforge do its focusing on that particular spot. (Watch it to make sure the red dot hits the piece of tape.)


100% this.


Since they are so small, the piece of tape might not work. You can enter the focus height manually using a calipers. Alternatively, you can tape one piece that you don’t intend to engrave and use that one for the set focus target. Many of us have successfully engraved glass and reflective items.

Glowforge support staff does not monitor this forum, so if you want them to weigh in you will need to contact them through the Support tab.


Hi everyone,

Thank you for your helpful comments. I use it scientifically. The thickness of the tape should affect the focus on the actual workpiece. Nevertheless, I guess I can adjust it by negatively defocusing the laser according to the tape thickness. Thank you for the useful info! Also, if anyone has any takes on my idea or any other suggestions, I am happy to hear them.


The thickness of the tape isn’t going to effect the focus of the laser enough to take it into account. To get a purposeful defocused score you need to make it a good 1/4" different before it’s noticeable.


I must confess I am a little doubtful about this. I get pretty different results when defocusing only 0.3 mm compared to the autofocused option. But I am not talking about scoring glass here, though.

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