Interactive Multitouch Display

Step 5 Prepare acrylic

It is valuable to polish the edge of the acrylic to maximize the light that enters from the diodes. Some folks advocate drilling holes in the edge so the leds seat down in but they seem to work ok just butted up against the polished edge. Start with 200 grit sandpaper and work up to 600 or realms beyond. Sanding always takes longer than you think.

Comments

[JamCat]

  I used to work in a plastics shop, and I guarantee the best options for nice clear edges are flame-polishing or clothwheel-wax buffing (but as buffing is pretty straightforward, and similar to other media I won't go into any tips)...
Flame polishing is really the best, and potentially fastest, but you should really practice on a similar thickness scrap first because you risk burning if you move the flame too slowly. I recommend using an oscillating power sander with 200 grit, then 600 grit til the edges are silky smooth. Then use a MAPP or hotter (for best results, we even used to use oxy-propane smallllll tip) torch to *QUICKLY* run the furthest tip of the feather of the flame around the edges at a backwards angle (so the cone is pointed opposite the direction you are moving) - after all dust and masking is cleared from the edges. You'll see the hazy sanded area turn clear and reflective very quickly if you are looking at the right angle.
If you miss a spot, or if some deeper sanding scratches remain, you can retouch with quick swipes keeping the flame even further back; if you burn it (and its VERY easy to do if you don't keep it moving) just resand the edge with 600 grit, and use some soap and water with a cotton (or preferably microfiber) rag to remove any scuz from the faces of the acrylic sheet. NEVER USE PAPER TOWELS ON ACRYLIC - they have wood pulp and will scratch it, eventually turning it cloudy...
This will give you nice crystal clear (acrylic is of course clearer than glass...) edges that will transmit wayyy more of your IR light!
Good luck!

[killersquirel11]

Would a soldering iron be able to do the trick? According to wikipedia acrylic melts at ~160c, and soldering irons tend to be able to break 200.

[Hossein]

Dear JamCat
i know what i wanted to ask is out of line but believe me i wouldn't ask if this was not my last chance .
I really really need to have the PDF version of this multi-touch screen here coz i took it as my major project and i have to build it in a week time and to be honest i don't have the money to be a pro member and since i'm a student i don't have any visa card as well.
I was wondering to ask if possible can you downloaded it for me and send it to my mail i would mean a lot to me .
THANK you so much
[e-mail]

[turkey tek]

wow jamcat, many thanks for the useful advice and insights!

[mike2008]

Hello, i'm haveing trouble getting the edges of my lexan to be clear. I have filed,sanded, and buffed and its still foggy... Is brasso the way to fix this? The lexan is 1/2" thick and it just had to be UV-resistant too, but it was free.:):)ha thats cool... so if anyone can help that would be great...

[Llewner]

Lexan is polycarbonate. What you want is Plexiglas (Acrylic). You can't polish lexan the same way as acrylic, nor will it carry the IR in the same fashion. In fact, in the DIY world, lexan is often used as an IR FILTER! So, umm, maybe build your own projector with it?

[Rjessick]

HaHA HAHAHA good call man... sorry mike..

[eecharlie]

Use metal polish!

I haven't tried it specifically for LEDs transmitting into acrylic, but in college I took a machining class that involved making an acrylic screwdriver handle. We used Brasso, available at most grocery stores (in the US).
See the results for yourself:
http://www.eng.hmc.edu/E8/Tools/ScrewdriverIndex.htm

This will also eliminate any tiny scratches you might get in the surface... but don't be too liberal, the metal polish is dissolving the acrylic so you can remove more material than you intend if you go overboard.