Acrylic Bolted Joints and Cemented Windows

assembled joint 2 - 300I'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.

joint drawings

The slots and tabs hold the alignment while the bolts fasten the pieces together.

screw layout


The blue protective film is still on the support piece.  That's why the edges appear a bit melted.

assembled joint

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.

assembled display stand

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.

assembled stand with LCD

 

assembled stand with LCD- side view

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.


Posted: 5 years 7 months ago by Jon Chandler #10235
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I didn't mention the purpose of the LCD display stand. No plans at the moment - I just wanted to test the window technique. Since I needed an opaque piece and a clear piece to see the effect, I needed two pieces of material.

Since I ultimately want a window for an LCD display, it made since that it fit a display. Because I needed two pieces of material and I'd been wanting to try the bolting technique, it made sense to include a bolted joint.

Combine these pieces and it only makes sense to make something useful!
Posted: 5 years 7 months ago by RangerBob #10236
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Hey Jon,

Nice piece. Having only just started playing around with laser cut acrylic, I'm just a few steps behind. Was looking into the captive nut bolt solutions too.

Just a quick note about the LCD window, does it have to be glued at all? We have an existing product using a similar scheme; using a stepped window (steped to retain the window in) which is simply sandwiched by the LCD frame. It holds great, no rattling at all once the OLED is tightened down. Obviously the downside is the window has to be milled (not laser cut) to get the step.
Posted: 5 years 7 months ago by Jon Chandler #10238
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A window with a rabbit milled around the edge would be a nice solution! I'm surprised that nobody (as far as I know) supplies pre-made windows in standard dimensions. Windows sized for 2x16 and 4x20 LCDs would cover a lot of situations.

A window like that could just be held in by the display pushing against the back as you say or could use a double-backed tape frame to hold it (some commercial enclosures do this) or it could even be glued in using silicon glue for a waterproof solution.

From what I've read, routing and sawing don't create the high residual stresses like laser-cutting does. It's kind of surprising that what seems to be more the more brutal machining methods are better for the material. I learned about the stress issues when I had something laser-cut and there was some residue left on the piece. "That will come right off with some rubbing alcohol" as was told when my parts were handed to me. I wiped the piece with an alcohol-soaked paper towel and the entire cut edge instantly had hundreds of cracks extending a couple mm or more.
Posted: 5 years 7 months ago by Jon Chandler #10239
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I just did a little research on "4x20 LCD Bezel" and it turns out that there may be some solutions.

DH MicriSystems looks like the best bet.

If you have ever looked for a bezel for an LCD 4x20 text display you have probably discovered the same thing we did--it does not exist (until now). This bezel is injection molded ABS to which we adhere a clear 20mil polycarbonate lense to protect the LCD face. This part really dresses up your LCD projects by covering the cut edge of a face plate and hiding the metal frame of the LCD itself.

All this for only $3.50. Nice.

Proud Industries also offer some LCD bezels and at least one of their products is in stock at Digikey. Alas, none of their offerings seems to be the size I need.

Posted: 5 years 7 months ago by be80be #10240
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You can buy LCD bezels from Newark and digi-key

Newark are hard to find but here a link to digi-key http://search.digikey.com/scripts/DkSea ... LCD+bezels

And http://www.mouser.com/Search/Refine.asp ... D%2bbezels
Posted: 5 years 7 months ago by Jon Chandler #10241
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Digikey carries (some of) the PRD series from Proud Industries as I linked above. They don't seem to come tall enough for a 4x20 LCD.

The Mouser ones are from a company in Germany. The EA 017-9UKE model (which is in stock at Mouser) is designed for a 4x20 display but it appears to be only the bezel without a lens.
Posted: 5 years 7 months ago by Jon Chandler #10290
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The bezel from DH MicroSystems arrive today. It's exactly what I need.

It's a bezel frame and a non-glare lens. The opening is sized for the active area of a 4x20 LCD display. The blemish in the upper left corner is the peel-off film - it's not a defect in the lens.





The bezel overlaps the panel opening by about 0.125" on all sides which will cover a rough opening.

Nice product for the price.
Posted: 5 years 7 months ago by be80be #10295
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I ordered a new LCD for a laptop I repaired and the peel-off film looked like the LCD was cut with a knife I almost sent the dang thing back.

Those are nice Jon looks like the same place you get the LCD would keep them.

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