acrlyic crackling

okay - yet another question here - this time its about something I've done by accident before but this time I would like to try and do it in a controlled way. What it is is that I have some letters cut out on a pc of aluminium sheet that i'm laminating on to some acrylic sheet. This acrylic sheet is illuminated with some LED's. I want to accent the letters a bit more then they are (the light doesn't reflect out of the smooth side of the acrylic very easily) and was thinking that I could try and create some surface or body imperfections that would allow the light to reflect at those points. I have in the past crackled acrylic but don't remember how. I think it was flame polishing and then putting some sort of solvent on top of that.

Any ideas or alternative suggestions? I've tried sanding, wire brushes, etc. but the surface has to be very gouged to see the light.

Thanks,

Reply to
James Varga
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My experience has been that overheating the material locally where machining occured helps to exacerbate crack propogation. To make cracking worse, use some alcohol as a coolant. However, I'm not sure you're gonna be able to do the above in any type of controlled manner.

How about engraving/machining the letters with a 45° countersink? That allow the area where you want the light to escape to better face the reader. ...that is if I understand your objective correctly.

Mask and bead blast? That would roughen up your surface, no?

Good luck.

Reply to
skuke

Acrylic "crazing" is caused by wiping an aggressive solvent like MEK, Aceton or Paint thinner onto the of your Acrylic surfaces. Smear it onto the surface with a rag and let dry. Repeat a few times. It may take a few days until a myriad of light reflecting micro cracks do show up in your acrylic letters. I am delighted to see that you have found a use for what is terrible problem in civilian and military air craft maintenance. hanson

Reply to
hanson

Won't the above solvents "melt" the surface too quickly? I've never used MEK or thinner on acrylic, but I seem to recall that acetone destroyed my part pretty quickly.

Reply to
skuke

Several different ways to do the job. Sandblasting produces a frosty surface very quickly although you do need to mask the surface for best work. Craxing with MEK or other strong solvent as mentioned in another post will produce a nice cracked surface. The surface becomes a bit more random with this process. Finally, abrading the surface with a wire wheel, stone or cutter will again produce the necessary exit angles for getting the light out. Any other process that will make the light hit the surface of the plastic at an angle smaller than the frustrating angle of internal reflection will do nicely. You can also apply a clear frosty tape and get the light out if desired.

-- Why isn't there an Ozone Hole at the NORTH Pole?

Reply to
Bob May

skuke wrote: I remember cleaning some acrylic piece in a heated ultra sonic bath at about 70'C and when I took the piece out to rince them in cold water crazing happen all over the piece.In this case all the piece were ruined,I had to make new ones. Cheers! Phil

: : > Acrylic "crazing" is caused by wiping an aggressive solvent like : > MEK, Aceton or Paint thinner onto the of your Acrylic surfaces. : > Smear it onto the surface with a rag and let dry. Repeat a few times. : > It may take a few days until a myriad of light reflecting micro : > cracks do show up in your acrylic letters. : > I am delighted to see that you have found a use for what is : > terrible problem in civilian and military air craft maintenance. : > hanson : >

: Won't the above solvents "melt" the surface too quickly? I've never used : MEK or thinner on acrylic, but I seem to recall that acetone destroyed my : part pretty quickly.

: -- : Skuke : Reverse the domain name to send email

Reply to
Philippe Gravelle

Acrylic Crackling?

Is that what you get when you roast the chemically-overloaded joints of meat from some of the supermarket chains?

Reply to
Airy R. Bean

Okay - I'm just looking through my shelves and I have white spirit, Methalated spirit (Is that MEK?) and acetone - what out of those would work the best?

Also - does heating it help? or heating the material first and then applying the solvent?

I've tried this with very poor results. The light source I have isn't the strongest and refraction isn't very high with very shallow abrasion.

I've tried this as well as frosting spray with poor results.

Reply to
James Varga

Masking tape to isolate the goodies. Abrade the surface with fine sandpaper or a little sand blasting to frost it. A narrow scratched strip just barely outside the border of the letters will be very effective. You want to kill total internal reflection at the smooth surface to let the light out.

Reply to
Uncle Al

Reply to
David Billington

Wipe it with PVC cement and sprinkle glitter over it...

Reply to
Kevin Beitz

I have in the past crackled acrylic but don't remember how. I think

I've got some to crack with regular Rubbing Alcohol. Take a rag soaked in it and lay it on top. Put a piece of sheet metal over that to keep it from evaporating quickly. The cracks usually do not show up right away though.

Another thing that can destroy acrylic is getting it near some loctite products. That cracks near immediately.

Chris L

Reply to
Chris L

Hey folks, the goal is the goal not the path. Mask surroundings with tape, abrade the acrylic with fine sandpaper or sandblasting. Remove the tape. It isn't rocket science.

If you solvent-craze acrylic the damage will propagate over time.

Reply to
Uncle Al

If you've got some lexan (polycarbonate) and you want to create a bubble texture all you have to do is pop it in a hot oven for a few minutes at 350/375 degrees F. The moisture in the plastic causes the bubbles. I'm not sure about acrylic. Maybe if you soaked it in water over night and then put it in a hot oven.

Reply to
tomcas

Polycarbonate is hydroscopic. YOu have to bake it ant about 200F for a long time before raising it to bending temperature or it will bubble. Acrylic is not so id takes a lot more heat to get bubbles.

The best way to get brightest light out of the letter shapes is to mask it off or use the metal overlay and bead blast it. If you light it from the edge the angle of incidence of the light will be so shallow that it can only get out through the etched areas and the edges.

Reply to
Glenn Ashmore

Reply to
Karl Vorwerk

With very few exceptions like teflon, all plastic is hygroscopic. YOu have to bake it ant about 200F for a long

I've used 250/275 F for 2 hours to bake out moisture, then raising it to

350/375 F for forming. Acrylic is

That's why I suggested an overnight soak in water. Have you ever tried it?

Reply to
tomcas

As I've mentioned above I have tried the sand paper AND bead blasting (I don't have any sand or aluminium oxide loaded up) and neither gave the effect I was looking for.

I like the idea of the cracking so will keep trying that.

Cheers,

J
Reply to
James Varga

When I mentioned "overheating the material locally..." (first post) I meant that the localized heat caused by machining created additional stresses in the material. Those stresses are what creates the crazing/cracking. The different solvents probably just weaken the material enough to allow those internal stresses to become visible and propogate.

Reply to
skuke

Try a very, very light sanding with 120 grid paper -- just sort of rubbing to get a few scratches on the surface. Then douse with the cheap rubbing alcohol from the market. Keep it wet for about 5 minutes. Let it dry, perhaps with light heating from below (electric blanket?).

Repeat a few times and you will have pieces with the largest dimension about

10mm.
Reply to
frank

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