"Flash back" scarring acrylic

[Belinda Barfield]

Laser: 65 watt Laser Pro Explorer
Material: 1/4" Extruded Acrylic
Problem: When cutting acrylic I am getting "flash back" from the aluminum honeycomb vector grid which is scarring the acrylic. I have tried cutting with paper backing on both sides - get paper burn with recommended settings and any variation of said settings that will cut through. I have tried cutting with Sticky Mickey mask, which is better, but still having problems. Best results, with least flash back, at 1.3% speed, 100% power, 1000 PPI, but still unpredictable flash back.

Any suggestions, recommendations would be most appreciated. Thanks!!

I will be unable to respond to your posts tonight, but will get back with you tomorrow, so please don't feel I am ignoring your good advice.

[Lee DeRaud]

Transfer tape, bottom-side only, seems to work for me. The stuff I use is from Sign Warehouse, what they call "medium-tack" IIRC. At the settings necessary to go through 0.2" acrylic, it singes slightly but does not burn.

[Joe Pelonio]

I'm in the process of engraving and cutting about 50 12x24 sheets of 1/4" acrylic into shapes for a job. The only time I had a problem was on the first run when I had the peak of a "roof" shape too close to the flat bottom of the piece above it. That extra air from allowed it to flare and blacken the paper on the peak. They were less than 1/16" apart. I moved the rows a bit farther apart and that solved it.

[Scott Shepherd]

I resolved this by getting the work up in the air. I have several things that are 1/2" thick, and I place them in various places under the acrylic, so it's 1/2" from the bottom of the acrylic to the top of the honeycomb table.

[Frank Corker]

I too raise mine above the honeycomb, I use golf peg tees, they fit in the honeycomb but lift it far enough off to avoid the tick marks.

[Keith Outten]

Something I am working on...a new vector table machined from Corian. Its a 12" by 24" piece of Corian with a 1/4" by 1/4" grid machined with a 45 degree router bit. The resulting surface is prism shaped and allows the air to flow unrestricted directly under the material being cut. My experience is that Corian won't flash when the laser beam hits it. The prism points are very sharp thus there is very little contact at the points but there are lots of points for support. The depth of machining is 1/4".

The picture below was generated by VCarve Pro, I should have the first vector table cut and ready to test this weekend.

.

[art baylor]

Keith:
Brilliant! The advantage of a pin table, but much simpler. Hope you can make a few bucks off this idea.
Art

[Rodne Gold]

We almost never use our honeycombs , we either elevate using blocks of 10mm pex or cut directly on the "table"
Why i put "table" in inverted commas is that we cut a sheet of black anodised ally to fit over the table , it absorbs laser energy and doesnt reflect it back as well as showing a white line when engraving on to it , the white line is great for outlines of objects and acts as a template.
Air assit , properly directed should actually stopp flashback or flaming damage.
Apart from that , most flashback occurs with honeycomb tables where the cells are slightly deformed , you can make a tool to "restore" the cells and make sure the walls and lips are exactly perpendicular to the workpiece

[Keith Outten]

I have a vector table that I purchased with my first laser engraver. I have used it in both my Epilog Legend 24 (35 watt) and the new Xenetech XLT-1325-60 at CNU. It is extremely rare to ever see any flashing or flaming on my Epilog...ever. The Xenetech will flash and flame constantly unless the absolute perfect speed and power settings are found. I have not found any speed and power setting on the Xenetech yet that allow me to cut acrylic mirror with reasonable quality unless I mask and cut twice. The Epilog will cut acrylic mirror perfectly without masking and without any flashing issues in one pass.

I expect that Rodne's comment about air assist is the reason for the huge difference in the two machines. The Epilog directs the air down to the cutting zone and the Xenetech has an air bar that doesn't move so I expect less air gets to the cutting zone area thus it is less effective. These are just my feelings at this point, I don't have any technical data to back it up. I can say that when vector cutting acrylic the older Epilog is my first choice for thin materials based on cut quality. For raster engraving the Xenetech is fast, the extra power is a huge benefit and the quality is near perfect with one exception and that is when using a masking material. Paper masking tape will cause flaming even when raster engraving on the Xenetech at higher power settings...mostly when engraving deep text on Corian signs so I try to adjust my paint fill procedure when I can to eliminate using a paper masking on Corian.

The lesser quality vector cutting I have experienced with the Xenetech on acrylic is the reason I have been working on an alternative vector cutting table design. There isn't much I can do about the air bar other than increase the air pressure which hasn't provided much of an improvement at pressures up to 40 PSI. Possibly an improved table will help reduce flaming along with some more experimentation with speed and power settings. I should also experiment with higher air pressure I guess to see if I can get more air to the cutting zone.

.

[Belinda Barfield]

Something I am working on...a new vector table machined from Corian. Its a 12" by 24" piece of Corian with a 1/4" by 1/4" grid machined with a 45 degree router bit. The resulting surface is prism shaped and allows the air to flow unrestricted directly under the material being cut. My experience is that Corian won't flash when the laser beam hits it. The prism points are very sharp thus there is very little contact at the points but there are lots of points for support. The depth of machining is 1/4".

The picture below was generated by VCarve Pro, I should have the first vector table cut and ready to test this weekend.

.

Please keep me posted on this. I have lots of Corian in the shop and this might be the easiest long term solution.


Air assit , properly directed should actually stopp flashback or flaming damage.

Apart from that , most flashback occurs with honeycomb tables where the cells are slightly deformed , you can make a tool to "restore" the cells and make sure the walls and lips are exactly perpendicular to the workpiece

Rodne, have adjusted the air assist to the best of my ability. Some of the cells are deformed and this is probably the main cause of the flashback. I'll try to restore those that are mishappen.




Paper masking tape will cause flaming even when raster engraving on the Xenetech at higher power settings...mostly when engraving deep text on Corian signs so I try to adjust my paint fill procedure when I can to eliminate using a paper masking on Corian.

.

Keith, I have had the same issue with paper masking tape - especially the type that comes on acrylic.

Thanks to all for your replies. My first step today will be to elevate the peice as several of you suggested. I'll keep you posted on the outcome.

I couldn't get back to y'all last night because I had to be committed . . . uh, I mean I had a commitment - yeah, that's it. :D

[Brian Robison]

Belinda,
I sent you a PM

Brian

[Belinda Barfield]

Thanks Brian. I e-mailed you.

[Belinda Barfield]

Lee, I have cut acrylic in the past with mask on the bottom only, with good results. The current application requires that I either keep the original paper protection on, or protect both sides with another material. There are several steps the pieces go through after I have cut them and there can be absolutely no scratches, etc., when the end product is delivered to the client. The Sticky Mickey works well, but I would like to avoid removing the original protectant.

I'm having some issues this a.m. also in that the speed/power settings that worked yesterday afternoon don't work this a.m. So, I am back to square one. It is very frustrating that I can find no consistency in speed/power settings and must run one (sometimes more) test pieces every bloomin' time I crank the laser up.

[Lee DeRaud]

Lee, I have cut acrylic in the past with mask on the bottom only, with good results. The current application requires that I either keep the original paper protection on, or protect both sides with another material. There are several steps the pieces go through after I have cut them and there can be absolutely no scratches, etc., when the end product is delivered to the client. The Sticky Mickey works well, but I would like to avoid removing the original protectant.Fair enough, but every source I have recommends removing the factory covering and (possibly) replacing it with something more appropriate.

(Of course, with the cheap stuff I use, the "original protectant" is some kind of clingy plastic saran-wrap stuff...I don't even want to know what would happen if I ran that through the laser.:eek: )

[Belinda Barfield]

Fair enough, but every source I have recommends removing the factory covering and (possibly) replacing it with something more appropriate.

(Of course, with the cheap stuff I use, the "original protectant" is some kind of clingy plastic saran-wrap stuff...I don't even want to know what would happen if I ran that through the laser.:eek: )

I'm using Acrylite which comes with a brown paper coating, which is highly susceptible to burn! I may have to remove the top paper, cut, cover again, and cut away the protectant I don't need. This ol' dog is trying very hard to learn new tricks!

Thanks again for all your help.

[Mike Mackenzie]

I learned a trick that the big laser boys use. We are talking about 1000 watt systems but I tried it and it worked pretty good.

What they do when cutting acrylic is to wet an old cloth towel lay that down on the table and then place the acrylic on top of it without any masking be sure the the towel is wet enough not to catch fire but not dripping wet.

We tried it and it seemed to work pretty good but we really don't have to much of an issue with flashback with the honeycomb so we don't use it to much only when we cut 1".

The other really important thing to be sure of is to keep the honeycomb cells CLEAN when liquid acrylic builds up in the cells it can cause flash points.

[Richard McMahon]

Hi Belinda.
I bought some 1/2" aluminum angle and cut it to the length I want and then lay them on their backs (like a pyramid) spaced as far apart as you like and I haven't had any problems with any burn back on the 6mm Acrylic I have cut.
I remove the paper from small parts as it's hard to get off after cutting but I leave the paper on for bigger pieces.
Rich.

[Andrea Weissenseel]

So far I did not have any problems with flashbacks. I don't place my acrylic directly on the honeycomb - I have a plastic grid, something like a plastic honeycomb about 15mm high, that I got from my dealer when I bought the laser. With that I have the poblem though that the edges of the acrylic are sometimes clouded also the plastic grid didn't withstand my machine for too long :D so I have it already in a couple of pieces.

A couple weeks ago I read a thread by Dave - he wrote that he uses rivets, that works excellent and Frank's tip with the golf pegs is a very good one too. You can place them on your table wherever you want to and you also have clearance underneath, so your exhaust can blow out the fumes so theay don't settle on the acrylic.

Andrea

[Belinda Barfield]

Thanks for the replies Rich and Andrea. The golf peg system never worked for me as I couldn't achieve a consistent level over the entire bed of the laser (20 x 38). My honeycome grid tended to sag in spots. Problem solved for the most part with a Corian vector grid based on a design on an original grid design by Keith Outten. I added holes for air flow and dowel placement for alignment.