LED sign help request

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LED sign help request

Postby fred ruppert » Wed Oct 03, 2018 5:25 pm

I have been making LED lit signs this summer, but am having a problem. When looking at the Plexiglas with the lights on, there are areas that seem to be clouded, are not clear. Is this common? Is there something in the processing that is creating this clouded area? or is there some residual adhesive that won't come off (I have tried Windex, rubbing alcohol and PlastX - plastic cleaner for headlights - without apparent effect). I have been using flame polishing on the edges and thought perhaps there was something in my technique that was creating the cloud effect, but I am also seeing it on my recent work where I have resorted to only sanding the edges.

When I say with the lights on, after one knows the areas, one can see the cloud if you can get the Plexiglas in the right light conditions


If you have seen this on your work, how have you avoided it, and or how to you get rid of it? HELP!
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Re: LED sign help request

Postby Xxray » Wed Oct 03, 2018 7:53 pm

Would help if you posted a pic, I would say either the pexi is flawed or you are causing it somehow. Best way to restore plexi is via buffing, but takes quite an investment to get a decent floor mounted buffer up to the task.
Best advise is to always leave the protective film on the side that isn't being worked on and is face down, until it is ready to use.
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Re: LED sign help request

Postby fred ruppert » Fri Oct 05, 2018 3:07 am

I am reconsidering, I believe the pieces I have made without flame polishing do not have this feature, but it is fairly common on the pieces that are flame polished, so I would like some advice on flame polishing.

Prep for flame polishing - yes I retain the paper on the down side of the Plexiglas when cutting, and only remove the paper on the top surface just before machining. Cast Plexiglas by the way. After cutting, I will sand the edges using up to 320 grip paper, blowing off the debris as it accumulates, remove the back side paper, and wash the piece with water and dish detergent. Drying with microfiber cloth.

When I flame polish, I hold the piece with a leather surfaced glove to protect from the heat, as the other hand passes the flame past the opposite side of the piece. I usually run the torch so the yellow part of the flame is against the Plexiglas, what I see on You Tube, they typically will have the torch further away, so that the blue part of the flame is touching the Plexiglas. I usually will run the torch so that the flame is perpendicular to the plesiglas, on You Tube it appears that they have the torch at a fairly steep angle to the Plexiglas. Are there elements on how I do the flame polishing that are creating this 'cloud' effect?

I have been unsuccessful in trying to add the picture of this 'cloud' effect, I havent figured out this website and how to use the Options Upload attachment feature
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Re: LED sign help request

Postby Xxray » Fri Oct 05, 2018 5:40 am

I use a professional buffer so haven't had the need to use flame in years. It would certainly be capable of marring the surface, if you paused for instance. Results can be sketchy which is why I switched to buffing early on, but with care and practice should be getting acceptable results. Don't know if you are using MAPP or propane, MAPP I think is preferable as its much hotter and does the job quicker, but you really got to pay attention to keep the flame moving and not letting it reach flash point.

Uploading a pic here is simple, just use the upload attachment function to find it on your computer and upload it ,, That is unless you have to have a certain number of posts to do it and you are below the threshold.
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Re: LED sign help request

Postby dwilli9013 » Fri Oct 05, 2018 12:58 pm

Well you have the master of edgelits giving you some very sound advice. I have followed his lead many times and have put out some awesome pieces.
I too used to flame polish all of my edges early on. I have since stopped this practice and the reason for that was following some of Dougs advice. I purchased a high quality "0" flute end mill in 1/4, 1/8 & 1\16" I then got some of my scrap from flame polishing gone bad and started experimenting with feeds and speeds. I found that the optimum speed and feed for me was when your chips from the cut are about the size of a babies fingernail. I also pay particular attention to the sound of my cut if I start to hear any humming or hint of chatter I bump my feed up a bit. Once I got my feeds and speeds under control I am able to cut up to half inch cast acrylic with near crystal clear edges. Post cut should I need to clean up any areas I have found that a good quality set of cabinet scrapers work the best. 6 to 12 good swipes with a quality scraper brings any blems I have back to crystal clear. I will admit that this method can be time consuming but I don't run a production shop either so when I start getting aggravated with the process or bored with it I will move on to the next project and come back to it later.
I currently work at a design studio in by Chicago as a side gig and now have access to some industrial type buffers that Doug had mentioned. This method indeed produces immaculate edges but one has to remember this method can also scrap a piece with the slightest loss of control. These buffers also show absolutely no mercy for skin! This I can attest to from experience. Ouch and it takes forever to heal. I have also found that sometimes the crystal clear edges take away from the piece but that's my own thoughts. Truly the final eye of the artisan or the customer is all that matters.

On the posting of pictures remember to resize your photos the max size to upload to the forum is 2 meg.
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Re: LED sign help request

Postby GEdward » Fri Oct 05, 2018 2:35 pm

These guys are the best as is their advice. With that said, if you are not wanting to invest in a high dollar solution to achieve perfection then taking the advice to use a good quality "0" flute end mill and fine tuning your feeds and speeds to achieve results that require less effort to polish the edges out is great advice. To your question about your methodology regarding the flame method I do believe you have an issue. The yellow part of the flame is yellow because it is comprised of carbon/soot. The blue to almost invisible portion of the flame is the sweet spot. It is the hottest and cleanest portion of the flame. The reason the You Tubers show them pointing the flame more or less toward the face they are polishing is to avoid the problem of the flame "licking" the bottom edge of the face causing it to heat prematurely and to prevent the flame from washing under the bottom surface where it can carry and deposit soot on the surface.
Also when cleaning plexi never use a solvent, ammonia based or Windex like cleaner. Mild soap, like Dawn, and water should do the trick most of the time. For the tougher cleaning or to polish out minor scratches use a good quality plastic polish.
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Re: LED sign help request

Postby Mobius » Fri Oct 05, 2018 2:35 pm

Just a note on your torch method Fred: The hottest part of the torch flame is just past the point where the flame ends, which is why you see people using the blue part on YouTube. Also, when you place the acrylic in the yellow flame, you are exposing the acrylic to incomplete combustion. I wonder if this is causing some of your clouding issues, if the acrylic is reacting to the unburnt/partially burnt fuel/soot.
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Re: LED sign help request

Postby Samson » Fri Oct 05, 2018 8:24 pm

First, don't use alcohol or ammonia on plexi, it causes damage i.e., crazing, cloudiness, cracking, etc. Windex has alcohol in it.
This may or may not be the problem or a contributing factor.
Also, depending on what is used to wipe with, there could be micro scratches.

The best way to remove the damage, is to do a progressive polishing process. This will require a buff motor and the appropriate materials. There is no reason for a buff jack (industrial buffer), any motor that can spin 1750 rpm is adequate.
The first step is to do something taboo... you will sand the surface. That's where the progressive process comes into effect.
If you would like the complete process, contact me, and I'll list the process. Remember, it will require a buff motor. HF has one that will do the job without effort.

Yes, it is necessary to start at the beginning, with the sanding. Buffing alone, will not remove the crazing. It could disguise it temporarily, but it will reappear. Sanding removes the damaged surface.
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Re: LED sign help request

Postby martin54 » Sat Oct 06, 2018 5:40 pm

Not quite sure where the alcohol causes damage comes from, I use IPA all the time :lol: :lol: Posting a picture might help, others have already covered the use tools for edge polishing. I get a pretty good edge using a bit designed for cutting acrylic same as the O flute mentioned I would guess. The other thing is that I sometimes actually want a frosted look on the edge because I think it can look nicer, depends on the job really :lol: :lol:
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Re: LED sign help request

Postby GeneMpls » Sun Oct 07, 2018 5:43 pm

I cut a lot of acrylic with a laser and can verify that the extruded will turn to cracks at the edges from the heat stress. I assume that machining will be less stress?
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Re: LED sign help request

Postby martin54 » Mon Oct 08, 2018 12:05 pm

GeneMpls wrote:I cut a lot of acrylic with a laser and can verify that the extruded will turn to cracks at the edges from the heat stress. I assume that machining will be less stress?


Depends on your speeds & Feeds :lol: :lol: :lol:

To much heat can cause stress cracking & crazing with cast very unlikely to cause any problems when machining but can cause problems when edge polishing especially if using an open flame to polish but it is less prone due to the way it is manufactured. Cast is poured & extruded is rolled & stretched so extruded has more internal stress to start with :lol: :lol:
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Re: LED sign help request

Postby fred ruppert » Sun Oct 28, 2018 1:36 am

I've been on holiday but finally back. I have taken the advice of the people on this forum that have responded, and have this week made 6 pieces with flame polishing without any clouding. I attribute that to the change in technique, pulling the MAPP gas flame back so that only the tip of the blue flame is doing the polishing, and changing to run the torque at a shallow angle to the edge that is being polished. Thanks for your help.
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