- Published: Monday, 27 February 2012
- Written by Jon Chandler
- Hits: 7832
I've been wanted to try a couple things with laser-cut acrylics. For a long while, I've wanted to try bolted 90° joins, often seen at Thingiverse. I started with information I found in How To: Make Cheap LaserCut Custom Boxes for Your DIY Electronics. I wouldn't quite make the patterns shown in the article work with Visio, so I created my own. My patterns are slightly different, in that I made the slot width the same as the nut dimension across the flats to better hold the nut. The result is a rigid joint that's easy to assemble.
The slots and tabs hold the alignment while the bolts fasten the pieces together.
The blue protective film is still on the support piece. That's why the edges appear a bit melted.
The next part of my investigation was if a lens could be cemented into an opaque panel for an LCD or other display. Often, an open hole may be ok, or using a clear panel, but in the project I'm working on, I want an opaque panel and a clear weather-resistant lens.
My first thought was to solvent weld a piece of clear acrylic in the opening (you might notice the opening in the clear support and the opaque panel are the same size). The gap between the two pieces (the laser kerf) is too big for a solvent-weld joint to work. I could compensate for this but there's a more significant problem. When a piece of acrylic is laser cut, the residual stress in the edge of the piece is immense. A solvent like alcohol will cause instant cracking and crazing of the edge. The solvent used for solvent welding reportedly has the same effect. Scratch that idea.
To get some gap-filling performance and to reduce the amount of crazing, I tried a two-part epoxy. I removed the protective paper/film from the front of the panel and window and covered the joints with blue masking tape, pressing it in place carefully so that the epoxy couldn't spread. I left the protective paper/film on the back of both pieces and used a straight edge to fill the joint with epoxy. I allowed it to set for a few hours before removing the protective film.
I'm not sure if the edge is cracked or the sparkled effect is due to incomplete filling of the joint. The window is secure in the opening but the appearance isn't completely satisfactory. I think if I decide to do this, I'll make the window larger and cover the edge with a vinyl-cut frame to hide the seam.
The photos below show the assembled display stand with an LCD installed. The LCD is protected by a clear window epoxied in place.
In conclusion, the screwed joint is simple and effective. It's a handy method of joining panels at right angles, especially where the joints may need to be disassembled (like an enclosure).
The cemented window is workable but the joined edges don't have the best appearance. The edge could be hidden in a number of ways, resulting in an acceptable appearance.