At around 4:20pm, a project running on Big Thunder failed. I was rasterizing an image onto paint covered glass when the glass panel shattered just as the laser started scanning.
The scan was running at 20-30% power at 22mm/s speed. It hadn’t been running for more than a minute or so when the glass suddenly fractured and broke into pieces.
I collected the pieces from the laser bed and put them into the box the glass came in. I attached the following picture to illustrate. In hindsight, I should have taken a picture just after the fracture on the bed.
I am at a loss for why the glass shattered. The glass was bought at IKEA, designed for the Malm furniture series as a protective and decorative barrier.
On closer inspection of the site where the laser had completed the raster, there doesn’t appear to be anything unusual. The paint coating appears to have been burned clean away across the surface and the glass etch itself actually looks nice.
I cleaned up almost all of the glass from the bed. There were a few fragments that dropped through the grate and a few fragments that flew into the back of the chamber where I couldn’t reach them. I don’t believe those fragments in the back will hinder operation of the laser, I just can’t reach them.
I don’t believe damage was done to any component of the laser, just destruction of the medium itself. I’m more shocked at this behavior in the first place. Under strain, glass can break like this, but I didn’t think the laser was sufficient to generate the pressure necessary to damage the glass.
According to the Wiki, glass and paint covered surfaces should be rasterizable with no difficulty. I double checked this before I used this medium. I even ran cut and scan tests on cardboard that came with the glass to verify the cut pattern and quality.
Any thoughts on what happened? Was the speed too low? Power too high?
I’ll be in this evening and should be able to help clean these out just so that another volunteer isn’t caught off guard.
As for why this happened, it’s possible that the heat built up at a point in the raster, which if it’s notable compared to the unexposed areas, could trigger a thermal shock (this is why non-boroscilicate cookware shatters when swapped from boiling water to cold water).
I’ve never seen it happen on the laser but I’ve also not done a raster on such a large area. Some glasses handle heat stress better than others. Got an image of the raster and about where in the image it was when it failed?
Glass is just plain goofy. I am willing to bet that this was tempered glass, as a lot of furniture glass is tempered so that it doesn’t create sharp shards when it breaks. And, tempered glass breaks under stress easier than regular glass. Plus, since it’s not a borosilicate glass, it is still prone to thermal shock. That’s where part of the glass is hotter than the rest and it cracks at the temperature boundary. And then, it’s tempered glass, so the whole thing breaks up.
