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How to side-light & drill frosted plexi ?

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Cooper

Joined: Mar 19 2006
Posts: 1770


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Post Sun Oct 18, 2009 2:50 pm

I need help, fellow Oz'ers !

I need to take a sheet of acrylic/plexi and illuminate the whole sheet so it 'glows' evenly . I don't have room to put the LEDs behind the plexi so I was going to paint one side of the plexi with a white primer (to help reflect light toward the front), frost the front by lightly sanding it, and then install LEDs shining into the side of the plexi, which would hopefully diffuse enough from the frosting to give the panel a nice even glow .

My question is two-fold.. first.. can anyone think of a better way to do this ? Second, if I go this route, does anyone have any helpful tips/experience they can share as to how to mount the LEDs to the side of the plexiglass (shining 'into' the side) ?

First I thought about trying to drill holes into the side of the plexi and stick a line of individual 3 or 5mm LEDs into the side, and epoxy or hot glue them in place . The problem with this is that 3mm LEDs really aren't that bright.. 5mm LEDs seem like they might work if I used enough of them but their viewing angle is very narrow, and since the width of the 5mm LED is almost the same as the thickness of the acrylic, I can't seem to reliably drill holes in the edge to sink the LEDs in without the drill bit walking just a bit toward one side or the other and making its way out the side of the plexi icon_sad.gif . (I don't have a drill press, the 'glass is 1/4" thick) .

I could try polishing the side of the glass and maybe using one of the original style thin LED strips , and use some scrap metal to make a couple 'rails' to hold the LED strip up against the side of the plexi, then glue everything in place ? Or I could try the same thing with individual super-flux LEDs . This would avoid the issue of drilling holes for the LEDs, but I have a feeling it wouldn't shine the light 'into' the plexi as reliably and more of the light would be lost . Also some of the LED pieces are only going to be a few inches so using strips would be a bit of a challenge as I'll probably have to hack them up a bit .

So I know many of you have installed or experimented with illuminating etched plexi, tell me, how do you do it ? Any tips are appreciated, this is a project whose deadline is fast approaching . icon_surprised.gif
corvettecrazy

Joined: Dec 17 2003
Posts: 4357
Location: moved (twice)


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Post Sun Oct 18, 2009 2:59 pm

Painting the back of it white is useless.

I would just take LED's and aim them at the edge of the plexi. If you want even glow, the more LED's the merrier.

Any other insight on the project?
Cooper

Joined: Mar 19 2006
Posts: 1770


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Post Sun Oct 18, 2009 3:26 pm

corvettecrazy wrote:
Painting the back of it white is useless.

I would just take LED's and aim them at the edge of the plexi. If you want even glow, the more LED's the merrier.


I guess maybe the old flexi-strips then ? I'll need to put a polish on the edges first I guess, the way it comes cut is with sort of a rough hazy edge . I'll probably primer the back of the 'glass anyway just to keep the light from shining out the back and into my face but, yeah, it might not help the output at all . :|

corvettecrazy wrote:
Any other insight on the project?


Halloween . Angry robot head . biglaugh.gif

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bad venge

Joined: Jul 28 2007
Posts: 3550


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Post Sun Oct 18, 2009 5:22 pm

I used frosted contact paper .... Far easier then trying to sand also I used cathodes
corvettecrazy

Joined: Dec 17 2003
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Post Sun Oct 18, 2009 5:51 pm

They also sell frosting in a can but cutting into the plexi with sandpaper should yield better results than something on the surface
bad venge

Joined: Jul 28 2007
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Post Sun Oct 18, 2009 6:08 pm

I TRIED frosting in a can and it melted/crazed th plexi I was using and ruined it icon_wink.gif
EricCartman

Joined: Oct 24 2008
Posts: 175
Location: Oregon


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Post Sun Oct 18, 2009 7:36 pm

I don't think it is going to glow all that much, unless you have something etched into the plexi...

Have you seen this before? http://www.evilmadscientist.com/article.php?story=edgelitcards

Has some cool ideas. icon_smile.gif
Cooper

Joined: Mar 19 2006
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Post Sun Oct 18, 2009 9:39 pm

EricCartman wrote:
I don't think it is going to glow all that much, unless you have something etched into the plexi...

Have you seen this before? http://www.evilmadscientist.com/article.php?story=edgelitcards

Has some cool ideas. icon_smile.gif


Yeah, that is cool ! I saw it once before, maybe you posted it a while back ?

For the face though I need the entire red portion of the eyes to illuminate evenly, so I don't think etching will work . I could do like a network of lines drawn closely together or a web of crosshatches, but I don't think the effect would be nearly as good . icon_neutral.gif
Somehow I've gotta figure out how to diffuse it .
Blazin'88Buick

Joined: Jun 11 2006
Posts: 117


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Post Wed Oct 21, 2009 9:10 pm

What I've Heard works is only sanding the portions that you want to light up. That way only the image will show and not the rest of the sheet. Also strips of LED's or Cathodes should work really well.Hope this Helps some. Good Luck!!!
Phil
Owner, Oznium.com

Joined: Feb 11 2003
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Post Wed Oct 21, 2009 9:30 pm

How about the ribbon LED strip?
byte

Joined: Mar 25 2009
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Post Wed Oct 21, 2009 9:56 pm

Cut the robot head out of black paper and cover the plexiglass with the paper.
bad venge

Joined: Jul 28 2007
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Post Thu Oct 22, 2009 5:31 am

I think if you'd take the design to a sign shop , have it cut out in black vinyl and put several inch "wings" on both sides , then apply it and wrap the wings around cathodes on either side it should show up fine / A layer of white or silver reflective on the rear with a black cover would make it brighter ...

Or go old school and dollar store contact paper and an exacto knife on the cheap side
Cooper

Joined: Mar 19 2006
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Post Thu Oct 22, 2009 9:03 pm

byte wrote:
Cut the robot head out of black paper and cover the plexiglass with the paper.


Pretty much what I'm doing, except I'm using a a placemat that I bought at Target . biglaugh.gif It was the right thickness, and was rigid enough to support itself after having the face cut out of it, but still flexible, thin, and soft enough to (hopefully) not making cutting or mounting too difficult .

bad venge wrote:
I think if you'd take the design to a sign shop , have it cut out in black vinyl and put several inch "wings" on both sides , then apply it and wrap the wings around cathodes on either side it should show up fine


Not a bad idea but I'm already overbudget . :D

Phil wrote:
How about the ribbon LED strip?


I ruled out the ribbon strips for a couple reasons . The LEDs are more widely spaced than the old style LED strips, and there won't be very much space between where the LEDs mate up with the plexi and the first edge of the face that can be seen from the front, so there won't be adequate space for the light to diffuse.. you'll see the individual spots . Also, the old flexi-strips are virtually the same width as the thickness of the plexi so its very easy to mount; the ribbon strips would have some overlap that would be hard to deal with considering how I'm mounting the plexi layer to the cardboard box head .

Blazin'88Buick wrote:
What I've Heard works is only sanding the portions that you want to light up. That way only the image will show and not the rest of the sheet.


That looks cool for like cutting in or frosting out logos and graphics, but for the face I think it'll look weird if I have a whole sheet of visible plexi on the front of the head .

corvettecrazy wrote:
They also sell frosting in a can but cutting into the plexi with sandpaper should yield better results than something on the surface


I thought the exact same thing . I went by Home Depot today to get some white primer figuring I was going to rough sand the front of the plex, then experiment with painting the back white for more reflection . (Already tried a 'chrome' paint and black with poor results) . On a whim I picked up some frosting and experimented with it tonight and I'm thinking now that its the way I'm going to go .
You're right in that the frosting is sitting on top and not 'cutting in' to the plex so its not diverting light out the front like a deep etching does . BUT I found out what its really good at doing is scattering light back into the plexi, so if you frost the -back- of the plexi, and then shine the LEDs in, it does a pretty good job of scattering the light evenly out the front .
Side by side with rough and fine sandings the frosted test looks almost identical in total brightness and the finish looks -much- more finished and professional . The sanding might be just a smidge ahead in overall light but its very easy to make out the rough scratches of the sanding process, even after a lot of random sanding . I was thinking of getting a power sander to give it a more even appearance but I'm really pretty happy with the frosting and I think I'll end up going with that . Another bonus is that there's a smooth glass-clear front to the plexi facing out so it looks a bit cooler from that as well .

Tomorrow I'm going to experiment with going over the frosting with either black, white, or silver to push more light forward through the plex and see if its any noticeable improvement . Ah, the things we learn . :D

Thanks for all the feedback, guys ! icon_biggrin.gif
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