My brother taught my wife how to cut glass. She was a pro after one lesson. He owned the local glass company and did it 1000 times a day. Remember him suggesting she staple some cheap carpet stretched smooth over the workbench. Lay the glass flat on the carpet. You don’t have to use much pressure at all to score the glass with a good cutter. If you use a lot of pressure it creates micro-shatters in the glass and the break will not be clean. Also never double score the glass for the same reason. One clean fluid score (straight or with smooth curves).
Perhaps I should have added ’ push the cut with the back end of the class cutter - not your finger ! '
I actually wonder if the best approach is to use a GlowForge to mark the glass and then trace the markings with your oiled glass cutter. I was planning to use a similar approach to mark thicker pieces of wood before using my jigsaw.
Could be just a case of my general ignorance, however, isn’t the glass used on 3D printer beds treated, or special, in some way to better cope with the heat and won’t the treatment interfere with cutting it?
Some people use special glass but I use plain 2mm glass used for picture frames or 3mm mirror glass. The heat isn’t a problem as long as it is evenly distributed and the sheet is free to expand, i.e. not rigidly constrained at the edges. I use picture frame clips that allow a bit of sideways expansion.
I heat to 130C and cool rapidly with a powerful fan. The thermal shock never breaks the glass but occasionally parts stick too well and pull out chunks of the surface. That is the only failure mode I get (other than dropping something heavy on a machine) but they generally last me for years.
Here’s some advice I had a while back when this came up before:
I thought exactly this, tried it, and it really doesn’t work well. The laser engraved glass is essentially explosions on the surface of the glass, which make it extremely hard to run the scoring tool over smoothly, and prevent the score from working perfectly.
This was a good read if you are curious what’s happening with the glass under the laser:
I gave it a try a while ago and also didn’t have much luck. I figured I’d share some super-macro photos I took of the cut lines…
First, two shots of glass that was cut using a traditional glass scoring tool. I should mention that I haven’t cut much glass. The tool is pretty easy to use, easy enough that you can get the job done on your first try, but it’s possible that this is an exceptionally poor quality cut. Regardless of the quality, this split the piece of glass in twain.
And three shots of lasered glass. None of these were good enough to make a reliable break.
I did actually successfully “cut” the glass using the laser, but the cut quality was pretty bad. I think the settings I used were 50% power (my laser cutter has a 30-watt tube) at 14mm/sec - two passes. I was able to cut out a 3"-diameter circle that wasn’t terrible but also wasn’t very good… not good enough to call a “success”. (Ignore the writing, I used this piece of glass to test out engraving settings as well.)
I tried everything I could think of. I used different power levels, different speeds, multiple passes (up to 10 in one case), and defocusing. I even did few tries where I did two passes with a slight offset between them; I was hoping the heat generated by the second pass would crack the score line made in the first. No such luck. I also tried different defocus amounts with the offset passes as well.
I didn’t try any glass other than this one piece, perhaps it has some property that makes it harder to cut or something. I also don’t think I tried messing with the frequency - frankly, the frequency setting is basically a mystery to me so I don’t mess with it too much. OK, I guess I didn’t actually try everything I could think of.
You can see the glass cutter results in an unbroken score line even though it also has some fracturing around the edges.
The laser cut does not have a continuous score line amongst the fracturing. Since the glass breaks along the score it won’t crack & break cleanly without the continuous score line.
This is going to sound weird, but from the pictures it looks as if the laser is excavating bits of glass from a u-shaped channel rather than making a really narrow score. Which would mean not a strong enough stress concentration. Of course that could be completely wrong.
Here is a link to some info that @soldiercoleman originally shared.
Awesome post! I think that you and I have done very much the same process trying to figure this stuff out. These pictures are fantastic and very similar to the ones I looked at under the microscope we have in the lab, but wasn’t sure how to take a picture of with a cell phone. I think one interesting thing is that the laser affects the glass in all different directions, and that the scoring tool has some noise on the surface, but is essentially producing deep cracks in the direction of the tool travel. This is consistent with the shards produced by breaking the glass - with the scoring tool, which broke the glass easily where I scored it, there were few shards but they tended to be long, thin and skinny. Like terrible splinter fodder. With the laser, I could break it occasionally along the ‘score’ that I wanted, but often could not, and further more, all the breaks produced many small crumbs of glass, that were small and roundish. (potentially the glass that was inside the scallops of the laser path from your pictures?) I believe that the low success on breaking with a laser score has to do with the stress from bending the glass doesn’t know where to travel, and therefore often seems to veer off in random directions. With a scoring tool, which is producing long clean cracks in the glass, the stress from bending runs along those lines more readily and will travel around some pretty interesting paths.
I also had some problems with the high heat causing cracks. Someone suggested to use a wet paper towel over the glass for better engraving, which I haven’t had a chance to try as an aid for cutting yet. (However, on top of all the things you did, I also tried soaking in some cutting oil, which I’m told seeps into the cracks and helps ‘push’ the glass apart - did not help)
That does work as will a light film of dishwashing soap which you can rinse off afterwards.
No, I like hearing detailed results
How many repeated engraves/scores would it take to get through a pane of glass, or is that a terrible idea?
about the same as the number of licks to the center of a tootsie pop… (aka no idea ;-))
So what is the final verdict?
That’s a good question. I didn’t notice 2-3 passes making much of a difference depth-wise, but maybe many more would do something? Someone at the office just passed along a tip to me saying that you might be able to run a lot of scores (unfortunate naming in this thread – what we call engraving along a vector line) and then do one really high power pass to force the glass to crack from the heat, and it should crack along your laser-score line??? Will try and report back.
Lasering a mirror might not work but will it hurt the Glowforge itself? i.e. lasers reflecting wildly and frying essential GFbits?