Issues with engraving on Pyrex

I have done these pyrex casserole dishes since I got my laser a couple years ago, usually no problems. I picked up some new Pyrex dishes for some Christmas presents for the nieces and nephews and ran into some major problems. The glass looks like is it cutting well, but once you go to clean them, they chip and flake out. I did three and two are real bad, one not so much, the bad ones have square features the not so bad is all curves and such. Power and speed are 100% power, 23% speed and 300DPI, using my ULS 50 watt laser, which is recommended settings and what has worked for me in the past.

Any suggestions as to less power, more/less speed or anything else to stop the flaking?

This one looks good in person, not so good in the photo:

Attachment 373388

This one is bad no matter how you look at it:

Attachment 373389

And a closer view:

Attachment 373390

Hi Brian,
I've been perusing the forum for awhile and though I'd chime in. On my (brand shall not be mentioned) 45w, the last glasses that I did, I ran at Power 60, Speed 100, 500 DPI. I used Kirkland dishsoap and rubbed a few drops over the area I was engraving. I also kept the air assist off during the dozen glasses I ran to keep the soap from drying out completely. This substantially minimized the chipping/flaking that I had when running dry without anything. I did have one oops where I missed a drop of soap that buldged and it caused the engraving under it to be slightly lighter than the rest, but it blended enough that it wasn't noticible to the customer. I've noticed from personal experience that some glass, even from the same box, will engrave differently than the rest with more flaking. I've also tried sticking thin packing paper squares with dishsoap on the glasses with varried results, for me plain dishsoap has worked best.
On some glass and acrylic, I've also found that setting my graphic as 70-80% gray and then running the laser with simple Dithering at 15-20% higher power, or lower speed if you're already at 100% power, gets rid of the raster lines and gives a smoother engrave. This has also helped with flaking on some glass.
Cheers, Jeff

color your graphics 70 or 80% black, 300 res is good, try 100 power @ 70 speed for starters, and let your ULS driver automatically choose the halftone or dither settings, it should REALLY make a difference... all those raster lines should change into a nice tight grid pattern...

When the Pyrex brand was sold to its new owner, they decided to stop manufacturing with the use of borosilicate glass and switched to tempered soda-lime glass, which handles heat differently. I personally do not offer sandcarving or laser etching of tempered glass products or material because of the potential liability, albeit minimal.

I am not sure when the change of glass material took place, but it could be playing a role in the different experience you are having.

Agree on the 80% black, and set ULS frequency to 325 vice recommended 500, but might also lower power a bit. You want to be micro-fracturing the glass. If you put too much energy into too small an area too quickly, the glass doesn't just fracture, it chips out. Micro-fractures look frosted, chip outs look wavy-clear.

However, just to confound things a bit, there is a small chance you were underpowered. I was doing several glass items on Thursday and found that some of the details were rather washed out; at first I thought it was due to chipping but the areas felt too smooth for that when I dragged the point of an awl across them. While pondering the situation, I idly bounced the handle of the awl on the glass over the engraving. To my surprise, some of the washed out details now appeared frosted! I started tapping across the remaining washed out details and they, too, began to whiten. Apparently, those areas got enough laser energy to create internal stress in the glass but didn't get enough energy to micro-fracture well, and the impact of the tapping allowed stress fracturing to occur.

That said, your pictures appear to show chip-out. Still, you might try a few forceful taps (no need to be particularly gentle!) with a metal rod or hard plastic tool handle on and around those washed out areas on your designs. If they whiten, then you were underpowering those areas (they could be harder spots than average) but, if you see more area that was initially white turn clear, your tapping is causing flakes to chip out and you were over powered.

Thanks for all the great info. I tried a couple things, first was the 60/100/500 with soap, that was ok, still left some obvious scanning lines and light and dark spots, although probably a viable product in real life, for some reason the cameras always show more flaws than the naked eye.

The second is with 70% black, 80/100/500 and dithering set to Half Tone, I don't seem to have any "Automatic" option there, it's either Halftone, Error Diffusion, or Black and White. Also used soap and got decent results.

Glen, as for the first passes not being enough power, I don't think that is the case as I was at 100 power 23 speed, and there is definite depth to the engraving. The two other results have very little depth and mostly just frosting of the surface.

I also wondered, glass cutters use mineral oil on their tools to cut, wondered if that would work better than soap.... running out of place to test on my now scrap dishes...

Sorry this one is upside down...

Attachment 373428

This was the last try

Attachment 373431

Brian

I do a large volume of tempered glass pan lids. I'm after a frosted look--very smooth with no voids. I run my 45 watt at 65p, 75s and 333 dpi, 3 passes. The logo is quite small so the whole thing takes less than a minute. I also use 80% black.

Except for this job I try to avoid glass.

Mike,

A question or two, is that run without soap? And, is there a way to run the same job three times without actually having to hit start three times? I.E. can I send it to the laser with it set to cycle three times thru the same path? I haven't noticed a "repeat x number of times" option in my ULS software, but I'm constantly finding new corners of it that I hadn't realized before.

Quote:

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Originally Posted by Brian Lamb

The second is with 70% black, 80/100/500 and dithering set to Half Tone, I don't seem to have any "Automatic" option there, it's either Halftone, Error Diffusion, or Black and White. Also used soap and got decent results.

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Been awhile since I've used my ULS driver so I was kind of going from memory-- found my pic of the advanced-tab 'old' driver, and also a newer driver online...

the old version here-
Attachment 373525
if you choose halftone, then click 'enable', the 'calculate' button would come into play, and pressing that would automatically set the contrast etc sliders depending on your speed/power/image density settings, and for me it was failsafe, it ALWAYS produced a nice photo engraving.

the newer driver here doesn't have the calculate button, which to me is a shame...
Attachment 373526

Oh... says the blind man... OK, I see under High Speed Enhancement is where you click Enable... you had me going there for a moment. I will give it a test run and see what happens. I have the old style driver by the way...

Brian
I don't use soap. I refuse to use wet paper, masks, soap, etc. I'd rather not do glass. This job is quite profitable so I experimented quite a lot to get a "manufactured" look to the image.

I know a lot of people have had success using such things but I'm stubborn about it.

For what it's worth, my LS900 is fantastic at engraving glass- the ULS was pretty good... the Triumph, unless it's 1" thick glass, not so much. The GCC, with all the photo settings it has, I've yet to get it to engrave glass without major chipping and fracturing.

It did take a lot of experimentation to figure out the 900, until I did, I got results like this:
Attachment 373673
--major banding, uneven, just overall bad. And this was one of the better ones.. ;)

Did someone say 'you must fracture glass' with the beam?
Here's the Triumph's test. Fracture was absolutely NO problem!
Attachment 373675
--and the wet paper towel wasn't of much use!

alas, I don't have pic samples from the GCC yet...

but this is how my LS900 engraves glass- for the most part, as some glass is finicky-
but this is a GOOD wine glass. The engraving isn't perfect, but pretty close...
Attachment 373672

a little closer up...
Attachment 373671

Here you can see how the 900 is actually burning individual random dots,
with virtually no apparent beam overlap, so the laser *appears* to
never hit the same place twice....
Attachment 373674
--which drastically reduces chipping and flaking...

The trick is, figuring out how to get my OTHER lasers to do this! -- and yours :D

Well, after experimenting with most of the suggestions, running the three times at 65/75/333 and letting the ULS software do the automatic setting turned out to be the best. Picture looks worse than real life, it actually looks very nice in person. But, I think I will quit doing the pyrex, not worth it for the narrow profit margin, although these were for presents for my Nieces and Nephews.

Attachment 373682