Mirrored acrylic problems

[Deane Shepard]

I had bit of 1/8" mirrored acrylic to cut. I cut it with the coated side up, the mirror facing down and the protective paper still on the bottom. Normally it cuts very nicely but every now and then, I get a flare of flames. More often than not, when it flares, the heat causes a distortion in the mirrored coating that leaves the mirror frosted along the cut line, essentially ruining the piece. There's no rhyme nor reason to it, but over the course of cutting a couple of hundred pieces out of about 22 12x24 sheets, I probably had 25+ pieces that had been ruined. Unfortunately, they tended to be the larger pieces so it probably cost me about 20% on materials.

Does anyone have an explanation for the seemingly random flaming? Any ideas on how to prevent it?

Deane Shepard
ULS M360

[Chris DeGerolamo]

Do you have the vector grid beneath the material? Often times with our work we will lift off the material from the bed itself with some ceramic blocks, felt, etc. We have an Epilog and I just cut some 3/16" clear acrylic and was getting the same problem. I removed the vector grid and rested the acrylic on the outsides of the bed beneath and the two metal supports "inside" the bed - problem solved. Just don't use the autofocus because the rulers on the edges will hit the bottom of the crossarm.

[Lee DeRaud]

When you say "protective paper still on the bottom", do you mean (1) the original protective paper and (2) bottom as in "toward the bed" or bottom as in "coated side of the acrylic"?

My normal acrylic cutting method is, remove all "factory" protection, put transfer tape on one side only, and cut with the taped side toward the laser's bed. (For mirrored, that means the transfer tape is on the 'good' side of the acrylic and I cut from the back.) No flame, ever.

[Joe Pelonio]

I do the same as Lee, and for thick materials where I suspect there might be flaring, I will spray the transfer tape with water before cutting.

[Alexa Ristow]

Hi Deane,

Transfer paper on the mirror side, facing the bottom of the machine. Make sure that the transfer tape is smooth with no creases or bubbles. If your machine has variable extraction points, try and get air flow across the bottom of the sheet. This seems to help prevent a buildup of gas that sometimes " pops".

Joe, I will try your idea of wetting the tape next time.... sounds great.

Bye,

Alexa

[Mark Ross]

We cut 1/8 mirrored acrylic with our Epilog 36EXT 45W 8 hours a day 5 days a week. We have our air assisted cranked way up and we never get any flare ups, flames or otherwise.

Our acrylic comes with a protective plastic sheet on the mirro surface, the back surface is grey and this is what we have pointed 'up' (the laser cuts the grey surface).

[Dan Hintz]

We cut 1/8 mirrored acrylic with... our air assisted cranked way up...
Are your edges relatively clear, or are they frosted?

[Deane Shepard]

I have the coated side up with the mirror facing down. The factory paper is on the acrylic side, i.e. the bottom of the sheet as it sits in the laser. It is on a cutting grid. There is no correlation between the flares and the cutting grid, i.e. the flares are not happening because the cut happens to run along part of the grid.

The edges are clear and smooth. It cuts fine, that is the edges are good and it is cutting all the way through the acrylic and the paper. There is no charring or burning of the paper. In fact, even when there are flares, the paper does not show any visible signes of burning. I've checked the settings that they are enough to cut all the way through without overpowering the cut. It is just that on a seemingly random basis, I get these flares that ruin the piece. I can cut two or three sheets without a problem and then have three or four problems on one sheet.

I'll try the suggestion of removing the factory paper and replacing it with transfer tape. The acrylic has all come from Delvies Plastics and the protective "paper" that is on it is not at all like the brown paper that is on regular (unmirrored) acrylic. It is white and seems a lot like the tape I use which is why I left it on.

Thanks for the interest and suggestions.

Deane Shepard
ULS M360

[Martin Reynolds]

You might try cleaning off the grey surface with a damp rag. Sometimes this happens with surface contamination.

[Mark Ross]

Are your edges relatively clear, or are they frosted?

Completely clear, we have the frequency set to 5000 Hz and the speed is set at about 18, power is 100%.

[Brian Robison]

You need an acrylic cutting grid. It will solve your problem.

[donald bugansky]

You need an acrylic cutting grid. It will solve your problem.

Where to buy acrylic cutting grid?

[Dan Hintz]

Local Borg, look in the lighting section... 1/4" egg crate light cover, white plastic, a few $s for a 2'x4' chunk.

[Mike Null]

Those are not acrylic and not the best answer. I believe they're made of styrene which produces a lot of smoke.

[Bill Jermyn]

As a side note, for blobs of melt that form on the bottom of acrylic, I've had luck with rubbing it with Brasso to get most of it off, then finishing up with Silvo. A ton of work, but it will save the piece.