Air Bubbles In Clear Acrylic Weld Joints

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Tricks of the trade for preventing those pesky bubbles. April 10, 2005

We have been having very little success welding clear acrylic with mitre joints. We are getting air bubbles and other imperfections in the joint. Has anyone done any good with mitre joints, or is this just not a good technique? We see the potential for a beautiful case, but the trial runs have not been up to par.

Forum Responses
(CNC Forum)
From contributor D:
What other imperfections are you getting? One thing to try would be to do the miter so that the inside has a small gap, such as if you set the machine to cut them at 44 degrees instead of 45. This leaves space for the solvent to fill and also allows any bubbles in the space to escape.

From contributor J:
This has nothing to do with how you rout, but it does have something to do with holding the joint closed. We know people who use clear foam tape to adhere acrylic to acrylic. You can't see the plastic and you can't see the adhesive. It comes in various thicknesses to fill the void.

From contributor W:
After working in the sign business for 10 years, I too found it hard to get a perfect bubble free joint. Sometimes it would be pretty good, though. I usually preassembled the box, then taped it together, then used my syringe filled with resin bond and ran it around the joints. I will say heat forming the bends has much better results.

From contributor G:
You are delving into a highly competitive market here. I've been in the plastic fabrication business for 16+ years now and have always kept the "acrylic box" business held at arm's length. You will be competing against many who will be fabricating from their garage with no overhead. I know because this is how I started. A router/jointer and a glue bottle will put you in business making display boxes. Anyway, I would suggest getting away from the mitre and butt the edges. You are probably using a solvent to bond the parts (Weldon #3). If there is any type of microscopic gap difference in your joint, you will get air bubbles. Even with a perfect joint, you will get air bubbles. It's the nature of the beast. There are 2 part resins available through Weldon that will help eliminate the air bubbles by filling the voids. These tend to be difficult to work with and are very touchy. A great solution to the challenge is to bond the pieces with a UV curing system. This will give you absolute perfection water clear joints. The system may cost thousands to install, however. The biggest challenge that I've run into is assembling these boxes with bubbles in the joints that the customer thinks look absolutely beautiful. The next day I could assemble a similar box with barely a hint of a gap or bubble that the customer thinks is junk. The scenario continues to keep me at arm's length.

From contributor P:
Just a thought - would a heat gun draw the bubbles out of the glue line before it sets?

From contributor E:
Yep, two part glues and a less than 45 degree angle are the way to go for mitred corners - usually only found on museum quality pieces.

Otherwise, routed/jointed edge with flat on flat joints (2 inside panels, others all outside panels) is the way to go. Our customers don't complain about the small air bubbles, but we are mainly one-offs to retail customers, so not the most picky of buyers. Weight on the joint helps a lot, but nearly impossible to do right on the mitre (not to mention that this solvent glue runs right out!). From a plastics fabricator.