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Larry Bratton
02-07-2011, 11:29 AM
I am making some acrylic items that require the edges to be perfectly clear (or at least as much as possible). The acrylic is 1/8" (3mm), I am cutting it with 40watt Epilog, with the paper masking on it at 10s/100p/5000f. I am having a problem with the joints, when glued with Weldon #3 or #4 crazing and making those areas unsightly.

I realize (Rodney) that annealing would probably cure this, however, I do not have a proper oven for annealing and subsequently that is not a good option.

I read an article while doing research, that stated edge damage could be minimized by adjusting the power and ppi. Any suggestions from you gurus relative to this? I was thinking of running some tests at different settings to see what I get, but I would appreciate the input. Thanks in advance.

Frank Corker
02-07-2011, 2:25 PM
Larry, usually the crazing is started when the acrylic gets too hot and later when cooled comes into contact with the acrylic glue. I have a 45w epilog and the settings for the 40 and 45 for the acrylic 3mm is 15s not 10s.
Go on youtube and look up Tapplastics (http://www.youtube.com/user/tapplastics) there is a whole slew of gluing methods there and use American brands of gluing agents.

There are a couple of things you could try. Keeping at 10s but reduce the heat (power) down to 75% will probably still cut through it. Use air assist.
Keep the acrylic off any metal surface, even if it is machstick height, might stop bounceback adding the heat.
Take that plastic paper off might help reducing the heat at the point where the beam hits and use air assist.
Not all acrylics are made the same. Have you tried a different type of manufacturer. I regularly cut 2, 3, 4, 5 and 19mm and have never experienced the crazing, this includes from 4 - 20mm having also used a flame generator.

Larry Bratton
02-07-2011, 3:08 PM
Larry, usually the crazing is started when the acrylic gets too hot and later when cooled comes into contact with the acrylic glue. I have a 45w epilog and the settings for the 40 and 45 for the acrylic 3mm is 15s not 10s.
Go on youtube and look up Tapplastics (http://www.youtube.com/user/tapplastics) there is a whole slew of gluing methods there and use American brands of gluing agents.

There are a couple of things you could try. Keeping at 10s but reduce the heat (power) down to 75% will probably still cut through it. Use air assist.
Keep the acrylic off any metal surface, even if it is machstick height, might stop bounceback adding the heat.
Take that plastic paper off might help reducing the heat at the point where the beam hits and use air assist.
Not all acrylics are made the same. Have you tried a different type of manufacturer. I regularly cut 2, 3, 4, 5 and 19mm and have never experienced the crazing, this includes from 4 - 20mm having also used a flame generator.

Frank,
Thanks for the input. Yes, actually recommended is 15, I normally use 12, but the mask is paper and I kicked it up a bit thinking it was needed to get through the mask and the acrylic. Product is Plaskolite Optix, name brand. I left the paper on it to prevent bounce back and that works. I'll try dropping it to 75%. How about speeding it up and running it twice? How about dropping the frequency, to say 2500 or 1000? When you flame polish a glued article do you polish after assembly? (I have watched all of those Tap Plastics videos) I can flame polish but all I have available to me is MAPP gas as recommended by TAP.
No doubt I am overheating it.

Richard Rumancik
02-07-2011, 5:07 PM
I have some doubts as to whether 2 passes will help - the first pass will be a blind kerf and the acrylic vapor has to turn around and exit from the top instead of blowing through. This will usually cause a lot of irregular marks on the edge.

I have never really seen a definitive answer to this problem. Lasers are great for cutting acrylic but when it comes to bonding the edges there are 2 main problems - the sensitivity to solvent adhesives, and the fact that laser cut edges will be rarely 90 degrees to the surface.

One reference (see link) suggests that removing 1/32" of an inch of material after lasering will remove the heat affected zone. That requires a router or sander (or your tool of choice) and is not practicable for much besides flat exposed edges. It will work in some cases. You don't necessarily have to get it back to a polished edge. But it adds extra steps and adds complexity.

Annealing has its own problems with shrinkage, distortion and marks on the surface. It is a different can of worms.

The writer in the link suggests cast acrylic is less susceptible to crazing. Maybe try to work with a plastic sheet manufacturer and see if you can get a recommendation on a material and adhesive combination that works.

www.artifacturestudios.com/blog/archives/317#axzz1DJPUHWi2 (http://www.artifacturestudios.com/blog/archives/317#axzz1DJPUHWi2)

Rodne Gold
02-07-2011, 5:12 PM
Use lots of air assist , use cast acrylic and use as little PPI/freq as you can get away with ,use a 2 part rather than flash solvent type glue method.

Larry Bratton
02-07-2011, 5:28 PM
Gentlemen,
I thank you for your input. Yes, Richard, I had already found and bookmarked that article. I had that on my agenda to try as a solution.
Unfortunately we are working with extruded and are married to it for this project, but will suggest cast in the future. My joints are actually good but I get these fracture s on the edges and it makes it look cloudy or unsightly at best. However, customer received a partial shipment today and he liked them ok. I don't like them though and intend to try and resolve the issue.

Larry Bratton
02-08-2011, 8:47 PM
Update:
Frank, ran it at 10s/75p/1000f. It cut it just fine and the edge was just as good as 5000f. Unfortunately it didn't solve the problem. I tried both Weldon #3 and #4 (which is slower) but no appreciable change.
Acrylite (Evonik) makes an adhesive that does not contain methylene chloride, Acryfix 1S0117. It states on their advertising that it won't cause crazing. I contacted them and here is the reply I received:
Larry,
Your question was forwarded to the Technical Service Department. You have a very common problem. Lowering the power is the best first step to reduce the stress and crazing. The Acrifix 117 has been used with good luck by some fabricators with this problem, but not all fabricators. The Acrifix 117 does not contain any methylene chloride and therefore is slower acting which sometimes helps reduce the crazing. I would certainly try it.
Annealing the sheet to reduce the stress is the best way to make the crazing not occur, but most people are not willing to perform this operation. Here is some annealing suggestions:
(he is referring to an attachment he sent)
I have also dealt with some fabricators that have used a heat gun to heat the laser cut edge and perform a quick annealing with success.
Please let me know if we can be of any help.
Best Regards,
Brian Fraser
Technical Service Engineer
I am going to order some of it and have requested more info on the heat gun idea. Thanks again for your input.

Mike Null
02-09-2011, 5:33 AM
Larry

There is a UV adhesive for glass which will likely work but it needs UV exposure to set. I have not used it but have seen some pretty impresive results.

Here's a different product from Loctite that may have potential. http://instantsolutions.loctite.com/flashcure_adhesives.php

Is this possibly something that could be formed with a router?

Larry Bratton
02-09-2011, 9:26 AM
Mike,
That is a very interesting product. I am going to see if I can get some of that also. Acrylite also has a UV cure cement also, however I gave it a cursory look. I am going to order some of their products too and may give that one a shot also.
I know where your going with the router idea, the edges still have to be polished though, due to my quantity I have to hold that operation to a minimum by using the laser cut edge. If you flame polish it before it is glued up your probably back to the same place.
Thanks very much for the info on the adhesive!

Edit: Choke! I checked the price of the Loctite 4306...$50.00 an ounce!!!!!! I doubt that is an immediate option. That must be some kind of good stuff coz Loctite is sure proud of it.