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Thread: Glueing acrylic that has polished edges?

  1. #1
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    Glueing acrylic that has polished edges?

    I have read and watched a video from Tap Plastics, that says after an acrylic edge is either flame polished or buff polished it should not be glued with acrylic cement as it will craze. Are you guys that are flame polishing adhering to this practice? What about using the buffing method, same thing? I am trying to make sense of this, if you flame polish an edge and then need to glue it to another piece, what do you do?
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  2. #2
    I've heard of crazing if it comes in contact with alcohol, but not with cement. I've solvent welded flame polished acrylic plenty of times. in fact, it hold up better if it is buffed or polished first.
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  3. #3
    Larry

    My supplier advised me to scuff the edge to be glued with fine sandpaper first. I hadn't heard about the flame polished thing.
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  4. #4
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    Actually I was surprised at this. The comment is made after the demo on flame polishing and buffing. This is in Quicktime format http://www.tapplastics.com/info/vide...mat=quicktime& . The problem with crazing is that sometimes it will not occur immediately, it happens after the customer has it and you might not even know about it.
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  5. #5
    I'm not an expert at this, but when I made quite a few shallow boxes to hold puzzles, some of them fell apart after a while, and I was using Weldon. For the replacements, I rastered the areas to be glued for some tooth and they stuck together very strongly. So my experience tells me the shinier and smoother edges don't work as well with Weldon, but maybe superglue is a different story.

    2 cents worth, dee
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  6. #6
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    Quote Originally Posted by Dee Gallo View Post
    I'm not an expert at this, but when I made quite a few shallow boxes to hold puzzles, some of them fell apart after a while, and I was using Weldon. For the replacements, I rastered the areas to be glued for some tooth and they stuck together very strongly. So my experience tells me the shinier and smoother edges don't work as well with Weldon, but maybe superglue is a different story.

    2 cents worth, dee
    Dee:
    Yes, I have had some issues with Weldon #3 not holding. The surfaces have to be perfectly aligned, absolutely flat or the stuff won't work at all. It is difficult to work with also. If you happen to drop any in the wrong place, you just ruined your work unless you want to work really had to polish it out.
    I am working on an acrylic project that has exposed edges. I am trying to figure out, if I polish these before gluing them, are they going to craze as the video said. I have not had much polishing to do, as most of the time, my laser cut edge is acceptable. In this case, it may not be.
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  7. #7
    Larry, I was using Weldon #16 - supposedly for acrylic sheet or so it says on the tube... not very impressive, but that's what others recommended so I tried it.

    On a related subject, I got some of that TV stuff, "U-Glu" which strangely enough works really well. I wanted to see if I could make a bond between clear pieces that would hold but not show. It is hard to cut into an exact shape, but it does hold without showing if you get it right. It's just like a piece of double faced tape without the tape or a giant stickydot.

    Have you used superglue? I've used it on many other plastics such as bakelite, catalin, pyralin and ivorite, but they have been all opaque pieces and not pure plastic. I should do some experiments with cast acrylic...

    Thanks for the info on Weldon #3, I won't be trying it! hahaha

    cheers, dee
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  8. #8
    Actually Weldon 3 or 4 works very well. I use both and nothing else. I can imagine crazing on extruded acrylic but I've never experienced it with cast acrylic.

    Do not press the joint. Doing so starves the joint and you'll get a weak joint.

    Here's an example.
    Attached Images Attached Images
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  9. #9
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    The propensity to craze depends on the glues you use and the type of acrylic , cast is more resistant to crazing than extruded , glues with agressive solvents like acetone and the like are worse than some others. The ideal glue to use is one of the Tensol ranges , don't use a capilliary type glue if you are gluing a T type join , you need a "filler" type glue , not one that "melts" one surface to another, If you use a filler (contains "disolved" acrylic or is a 2 part glue) , you dont even need the polished edges at the join as it fills in saw marks etc. You can try make your own "filler" glue , albeit its not ideal , but disolving a piece of the same acrylic in chloroform till it "thickens" up - you will need to experiment a bit to see what works for you.
    Flame polishing is an incredible stressful process for acrylics (as is laser cutting)
    You can de stress the material in an oven at about 70-80c for one hour for every mm thickness and you wont get stress cracking at all.
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  10. #10
    Quote Originally Posted by Mike Null View Post
    Actually Weldon 3 or 4 works very well. I use both and nothing else. I can imagine crazing on extruded acrylic but I've never experienced it with cast acrylic.

    Do not press the joint. Doing so starves the joint and you'll get a weak joint.

    Here's an example.
    AHA! My failure was no doubt from pressing (actually clamping) the pieces together. Thanks, Mike!
    Last edited by Dee Gallo; 01-25-2011 at 1:23 PM.
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  11. #11
    Yeah gluing up laser cut panels into display boxes is also a problem due to the fine taper of the cutting beam. I've had good luck flooding the joints with Weldon 3, but its not optimal. Better is to run the panels through an edger for a perfect 90 degree to 90 degree contact.

    But this Tensol filler type glue that Rodne mentions is pretty interesting. Anyone have a Domestic USA brand name and supplier?

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  12. #12
    From my understanding, Tensol is pretty much weld-on here in the states. weldon 16 is a little thicker, but its kind of a mess to handle. gel superglue is great.
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  13. #13
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    Dee,
    Weldon #16 in the red tube is a thicker version of #3. IMO it is more difficult to work with than #3. It is gooey and sets up very fast making it messy. Weldon #3 is water thin. It works via capillary action, when applied to two pieces of acrylic, it flows between the parts and actually "welds" the parts together by dissolving the acrylic and as it evaporates it hardens and creates the bond. I apply it using a very small artist brush or a syringe. One has to be very careful not to let any drip on to the wrong place. It actually requires very little to get a bond, but the parts have to be dead flush to each other. Rodney says don't use for a T joint and he is right. Best way to do a T if possible, is to cut a slot, drop in the piece, then cement it with #3. That works fine.
    I have not tried super glue. It is very expensive. A pint can of Weldon #3 will last a long long time,haven't bought any lately but seems like it is about $16.
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  14. #14
    Quote Originally Posted by Larry Bratton View Post
    A pint can of Weldon #3 will last a long long time,haven't bought any lately but seems like it is about $16.
    I can't get mine to last at all. I keep leaving the lid loose, coming back to find the can bone dry from evaporation You'd think I'd learn after the 3rd can
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  15. #15
    Over the years I have read a lot of different comments about the potential for crazing of edges. You will get different views and comments because as Rodne indicates it is very material and adhesive dependent. There are many acrylic suppliers and two main types of acrylic, but then there are "alloys" etc etc. So what works and does not work is very dependent on the materials you are using. If you are not careful what supplier you are using (eg buy generic un-branded acrylic) then there is more chance that you will stumble across something that does not work (even if it worked "last time".)

    What really worried me about acrylic is the possibility of crazing occuring some time after fabrication (weeks/months). The last thing I want to do is be held liable for product that I shipped and was paid for.

    As Rodne suggested, you can stress relieve in an oven but it adds new problems. You need to set up a very well-controlled oven (perhaps an old range could be modified but the temperature control and air circulation would have to be greatly improved). Then you have to suspend/hold your parts so they do not get any marks on them. If they touch a wire rack or even a flat sheet there can be a contact mark. Then you have the problem of shrinkage. The part dimensions can change upon the anneal cycle. Finally, any bends that are done previously (and they should be done before annealing) will try to relax, so if you had a perfect 90 degree bend it may come out at 85 degrees.

    If I sound less than enthusiastic it is because there are a lot of traps with fabricating acrylic. Juts know what you are getting into and cover all the bases.

    The least risky way of treating a lasered edge is probably to sand off some amount of material and mechanically polishing it to the degree necessary to get a aesthetically pleasing joint. But this is not practicable in all cases.

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