Mirrors cracking

[Bert Kemp]

I'm trying to engrave a USMC emblem on a mirror. I'm doing the back side and removing the backing leaving the emblem. Problem is because I'm removing so much backing the mirror gets to hot and cracks.
Things I've tried
Sprayed mirror with soapy water. this caused the backing to flake and not be totally removed.
Pausing the engraving every few Min's to let mirror cool. This works but make the job take an extremely long time.
2 passes at lower power but this still takes a long long time.

any other Idea's would be appreciated thanx

[AL Ursich]

Just a Wild AL Guess.... WAG... 4 passes at even lower power..... Your right... It's all about the heat.

What do you expect from a Retired Squid.... :)

AL E7

[Bert Kemp]

Thats what a jar head would expect from a squid :p wow 4 passes will take an hour plus.


Just a Wild AL Guess.... WAG... 4 passes at even lower power..... Your right... It's all about the heat.

What do you expect from a Retired Squid.... :)

AL E7

[Kev Williams]

I've busted mirrors and wine glasses with my Triumph but it was simply because of too much power--

What settings you using? More important may be what mirrors are you using? I did some customer supplied mirrors once, some of them took Cermark power & speeds just to barely get thru the backing with my 40w LS900, others engraved fine. Even so, I never broke one of them. Not sure if that's due to it being an RF metal laser or simply because 40 watts isn't enough...

I also have some cheap mirror tiles here that takes a lot to laser the back off. Last time I tried one in my Triumph it broke itself into tiny pieces. Your 60 watt laser has plenty of power to get thru the backing, and probably melt the glass (my Triumph will) but the glass can't tolerate that much heat...

Are the mirrors flat? I'm assuming you have a honeycomb table? If so, and the mirrors ARE flat, do you have say, a piece of 1/8" or so aluminum that you can set the mirror on? The aluminum may act as a heat-sink, absorbing enough heat to keep it from breaking...

[AL Ursich]

Thats what a jar head would expect from a squid :p wow 4 passes will take an hour plus.

That's about 4 BEERS too while waiting for the Laser to finish... :)

But what do I know... I have not fired my old Epilog Laser in over 4 years... Too many other toys to play with... :)

AL

[Mike Null]

Bert

I don't know how to equate dpi with the settings on a Chinese machine but I would try at the equivalent of 300 dpi. As the dpi is increased so is the dwell time over an area thus a hotter engraving area.

Epilog has a good example of the effects with various dpi settings. http://support.epiloglaser.com/article/8205/42829/laser-resolution-and-how-it-affects-engraving

[John Blazy]

I laminate glass for a living, therefore I heat glass up to nearly 200 C at times without breakage, so its not just heat, its UNEVEN heat that breaks glass.

You can heat glass up pretty high, as long it gets the heat somewhat uniformly. So maybe if I were you, I would program the laser to etch in certain sections across the whole pc, then again to fill in between. Another thing I would try would be to pre-heat the mirrors in an oven, then quickly place on laser bed and engrave.

remember - its point source heat that cracks cold glass, in which the temp variance is high, not overall heat.

[Bert Kemp]

Thanx Mike and John I'll try both those see what happens.
Al 4 beers and all the mirrors will be busted :D

[Lee DeRaud]

Are the mirrors flat? I'm assuming you have a honeycomb table? If so, and the mirrors ARE flat, do you have say, a piece of 1/8" or so aluminum that you can set the mirror on? The aluminum may act as a heat-sink, absorbing enough heat to keep it from breaking...I always use the flat aluminum engraving table rather than the honeycomb table for mirrors, mostly for the more accurate alignment. Don't know whether it's that or the fact that my 25W machine is limited to what Bert would probably consider "reduced power", but I've never broken one.

[Glen Monaghan]

I'm trying to engrave a USMC emblem on a mirror.

That's your problem right there! ;^)

Does it have to be glass mirror? I've done a bunch of regular and colored acrylic mirror, which engraves pretty much like acrylic, easy peasy.

[Bert Kemp]

You must be a dog face:p
Well no they don't have to be glass but I engrave these to pass out to Semper Fi Vets and I pay $1.26 for a 7" round mirror. If you can find 7'' round acrylic mirror for under 2 bucks a piece I'll gladly use them.


That's your problem right there! ;^)

Does it have to be glass mirror? I've done a bunch of regular and colored acrylic mirror, which engraves pretty much like acrylic, easy peasy.

[Bert Kemp]

Kev I run at 40% power and 325mmps spd, I think I'm at the suggested 300dpi I might have a piece of alum I can lay under the mirrors will have to see if I can find it. these are cheap thin maybe 4mm craft mirrors.


I've busted mirrors and wine glasses with my Triumph but it was simply because of too much power--

What settings you using? More important may be what mirrors are you using? I did some customer supplied mirrors once, some of them took Cermark power & speeds just to barely get thru the backing with my 40w LS900, others engraved fine. Even so, I never broke one of them. Not sure if that's due to it being an RF metal laser or simply because 40 watts isn't enough...

I also have some cheap mirror tiles here that takes a lot to laser the back off. Last time I tried one in my Triumph it broke itself into tiny pieces. Your 60 watt laser has plenty of power to get thru the backing, and probably melt the glass (my Triumph will) but the glass can't tolerate that much heat...

Are the mirrors flat? I'm assuming you have a honeycomb table? If so, and the mirrors ARE flat, do you have say, a piece of 1/8" or so aluminum that you can set the mirror on? The aluminum may act as a heat-sink, absorbing enough heat to keep it from breaking...

[Lee DeRaud]

If you can find 7'' round acrylic mirror for under 2 bucks a piece I'll gladly use them.I took a quick look...if I did the math right, 7" circles cut from 1/8" mirror acrylic sheet will be $3-$4 each, depending on how well you can limit the wastage. But you're not restricted to that size/shape since you'll be doing the outline cut yourself on the laser .

[David Somers]

Bert,

Assuming you already have the glass and really dont want to buy more stock if possible....
Al suggested 4 passes at lower power, which as you mentioned will radically increase your job time.

How about breaking the job into sections. Lets say the glass is breaking after 3 minutes of engraving. Band your job into roughly 3 minute sized sections. Run them at the power and speed you need to use. But, color each section or band differently so you can control the order of the job? Top band goes first. 3 bands down goes next spreading the heat gain to a new area, then down to the 5th section, then up to the second, etc. Dont know if it would work, but it might prevent the heat from developing so much on a long run, while allowing you to run at the same speed and power level. You would add a bit to the run time as it changes to each band. But the gain would be minimal. Especially compared with 4 lower powered passes.

Keep in mind I have not played with lasering mirrors. Just bouncing ideas around for you to ponder.

Dave

[Bert Kemp]

I tried pausing the job every 6 mins or so letting cool them doing more it took an hour to run the mirror. Just a big pita trying to stand there and pause and go


Bert,

Assuming you already have the glass and really dont want to buy more stock if possible....
Al suggested 4 passes at lower power, which as you mentioned will radically increase your job time.

How about breaking the job into sections. Lets say the glass is breaking after 3 minutes of engraving. Band your job into roughly 3 minute sized sections. Run them at the power and speed you need to use. But, color each section or band differently so you can control the order of the job? Top band goes first. 3 bands down goes next spreading the heat gain to a new area, then down to the 5th section, then up to the second, etc. Dont know if it would work, but it might prevent the heat from developing so much on a long run, while allowing you to run at the same speed and power level. You would add a bit to the run time as it changes to each band. But the gain would be minimal. Especially compared with 4 lower powered passes.

Keep in mind I have not played with lasering mirrors. Just bouncing ideas around for you to ponder.

Dave

[Bill George]

I am just wondering if a small fan inside the machine blowing directly on the glass and directed toward the exhaust port would cool the glass enough? I know they use forced air cooling in some machining applications.

[Ross Moshinsky]

Post a picture & your file. You'll get more accurate help.

[Glen Monaghan]

You must be a dog face:p
Well no they don't have to be glass but I engrave these to pass out to Semper Fi Vets and I pay $1.26 for a 7" round mirror. If you can find 7'' round acrylic mirror for under 2 bucks a piece I'll gladly use them.

Uh, no, that's my younger brother. I'm a retired boy in blue, slipper of surly bonds, and all that...

No need to find a 7" round acrylic mirror, you can cut your own.

Especially since you are giving these to Semper Fi vets, you should seriously consider switching to acrylic so's they don't accidentally cut themselves when they break the glass ;^)

[Bert Kemp]

I'm looking for some cheap acrylic sheets but what I've found so far is more then I want to spend to give away. We only have one little thrift shop in my town and they had a acrylic mirror there a while back I'll have to see if its still there.

Uh, no, that's my younger brother. I'm a retired boy in blue, slipper of surly bonds, and all that...

No need to find a 7" round acrylic mirror, you can cut your own.

Especially since you are giving these to Semper Fi vets, you should seriously consider switching to acrylic so's they don't accidentally cut themselves when they break the glass ;^)

[Mayo Pardo]

Google is your friend - just did a quick search for acrylic mirror rounds and found some 6 inch ones for 1.86 if you buy 25-99 pieces.
I've never bought from them & have no affiliation with them - just passing on info.
ShopPOPDisplays is the name.

[Bert Kemp]

Thanks Mayo best one yet

Google is your friend - just did a quick search for acrylic mirror rounds and found some 6 inch ones for 1.86 if you buy 25-99 pieces.
I've never bought from them & have no affiliation with them - just passing on info.
ShopPOPDisplays is the name.

[David Somers]

Bert,

Just curious. How many mirrors have you broken so far? 7 years each if I remember right? Might want to track that so you can stop when you reach your limit? :rolleyes:

[Bert Kemp]

4 so far and haven't tried any more till I figure out how to stop it. I think the alum p[late will work but need to find one first. No Hurry

Bert,

Just curious. How many mirrors have you broken so far? 7 years each if I remember right? Might want to track that so you can stop when you reach your limit? :rolleyes:

[James & Zelma Litzmann]

Bert,

We've been doing mirrors for about 10 years now. We had this same problem until we started placing the mirrors on silicon cooking pads, it helps cut down on the difference in temperature between the laser and the laser bed. It is a simple answer to a real problem. Good luck, hope this helps.


Zelma

[Bert Kemp]

will any old silicone mat do or are these something special? thanx


Bert,

We've been doing mirrors for about 10 years now. We had this same problem until we started placing the mirrors on silicon cooking pads, it helps cut down on the difference in temperature between the laser and the laser bed. It is a simple answer to a real problem. Good luck, hope this helps.


Zelma

[James & Zelma Litzmann]

I think any mat will do, we got ours from Wal-mart, it was one you could bake on.

[David Somers]

I think he means just the standard Silpat, or what is sometimes called silicon cooking parchment. It is used in cooking to keep things from sticking. I keep a few for baking and rolling out doughs and they are great. Try one in the kitchen as well as in the laser!

[Bert Kemp]

I think any mat will do, we got ours from Wal-mart, it was one you could bake on.


gottcha thanks I'll pick one up.

[Bert Kemp]

I think he means just the standard Silpat, or what is sometimes called silicon cooking parchment. It is used in cooking to keep things from sticking. I keep a few for baking and rolling out doughs and they are great. Try one in the kitchen as well as in the laser!


u2 LOL is to short LOL

[James & Zelma Litzmann]

This is something like I (but I am not a he) was talking about, Roshco RBS14R 11-by-16-5/8-Inch Silicone Baking Mat, Red. I has really made a difference.

337393

Hope this helps.

Zelma

[James & Zelma Litzmann]

Hey Bert, let us know if this works for you.

[Bert Kemp]

I've been super busy these past few day with the PGR haven't turned laser on in a few days but when I get a cahnce I'll let you know Thanks


Hey Bert, let us know if this works for you.

[Bert Kemp]

sorry this took so long but haven't done mirrors in a long time. I did buy a pad a WM and they do help prevent cracking. thanks to all who made suggestions

[David Somers]

Well yeah....but have you tried a silicon pad in the kitchen yet? Inquiring cooks with lasers want to know!!! <grin>

[James & Zelma Litzmann]

You are welcome any time, glad we finally knew something to help someone : )