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| By: cplkittle on Sat, 4 Oct 03:33:44 -0500
| | Plexiglas in custom car audio
Plexiglas or polymethyl methacrylate (PMMA) comes in many grades, and is called by many names. Acrylic, plexiglass, plexi and lexan being the most common. Acrylic is a compound used to make Plexiglas from chemical compounds that contain the acryl group derived from acrylic acid. Plexiglass (with 2 s’s) is a tradename or trademarked by a company named Rohm & Haas. Plexi is just a shortened version. Lexan is Polycarbonate, and reacts differently to tooling than Plexiglas.
Plexiglass is used mostly to protect amplifiers, distribution blocks, or other equipment from dust, and to keep friends away from the adjustments. While it is very common as just a clear sheet to protect equiptment, it is also very simple to bend, etch, polish, and manipulate to a desired effect. It only takes a little time and a lot of patience.
Cutting, edging, and drilling
Plexiglas can be cut with a jigsaw, table saw, bandsaw, or it can be scored (at least 25% through) and snapped apart like glass. When cutting with a table saw, it ‘snows’ hot plexi shavings, so a full-face shield is recommended. Jigsaw cutting can be aggravating because it melts back together in spots behind the blade unless you have an assistant to squirt water on the blade as you cut.
For edging effects, you can cut it on the table saw at various angles, or use a router with desired bit. When using a router, go slow, this will reduce chatter marks on the glass which will have to be sanded out later. Drilling plexi is also a challenge because it cracks very easily. Always drill through plexi into a piece of wood, drilling through plexi with nothing under it will almost always shatter it. You can drill it with the drill in reverse. This works the best, but leaves a little ring of melted mess where the bit comes through. If you hold the material down firmly close to where the bit is, you can go through it in foreward and into wood with out any cracking. The problem is that when the bit goes through, it threads the very end of the hole, and the plexi runs up the drill bit, so if it is held tightly, most of the time it will go through with minor chipping on the exit side. I always drill it in the fastest speed of the drill, if the bit is turning too slow, it only chips away the plexi leaving fish scale looking marks in it. After drilling, a countersink will normally finish out any small imperfections around the hole.
Bending:
Bending plexi is probably the most aggravating thing I have done. If someone out there knows of other tricks of the trade, please tell me!
There are several methods, all involve heat.
The first way is simply heating it slowly with a small torch and bending it by hand. This is a little nerve-racking… if you heat it too fast you get tiny bubbles, too much heat will discolor it, and too little heat it will break instead of bending. Patience and practice make perfect.
The second method would be to use a heat gun or hair dryer. This only works on 1/8” material.
The third method is using a ‘heat box’. First you would make a mold or template for the plexi to form to. Place the plexi on the mold and build a box around it. Then add a heat source such as a torch or heat gun. The heat should be able to enter and exit the enclosed area, passing over the plexi and the mold. A small hole can be cut in the box to allow it to vent.
The last method is to use boiling water. I have never personally tried this, but I look forward to it in the near future. Since plexi has a melting point of 130 degrees Celsius, and becomes easily malleable at 100 degrees Celsius, boiling water seems to be the ideal solution and should prevent bubbling or discoloration due to excessive heat. Once the desired bend is achieved, a quick dip in cool water will prevent any unwanted warping or bending.
Etching:
Etching plexi is easy to do, yet difficult to perfect. You can use a router, Dremel tool, or any etching device of your choice. One benefit of etching is the light capturing characteristics it creates. Even the smallest scratch will glow when light is introduces from a polished edge, lengthwise through the center of the glass. Plexi is almost identical to fiber optics in this manner. Frosting plexiglas is done by either sanding it with a fine grit paper (800+) or sandblasting with micro grit. One trick I have used a number of times is to have a vinyl sticker made at the local sign place ($5-$10), stick it to the glass, and sandblast the entire side of the glass. Remove the sticker and you have added a really nice professional look to your glass. Add some light, and watch it glow.
Finishing:
This is the most time consuming step. After a piece has been routered, cut, bent, accidentally scratched, or edged, it is time to polish it up to perfection. The first step is to sand it. Start with regular sandpaper, use the grit necessary to remove whatever imperfection you are trying to remove. Once you have all gouges, router chatter, saw marks, or other imperfections sanded out, switch to wet sandpaper. Move up in small increments until you get to 1200 or 1500 grit paper. The edge should appear perfectly polished when wet, and slightly cloudy when dry. Now you are ready to buff out the cloudiness with a cotton buffing disc or wheel. These can be found in most hardware stores. I use one that attaches on to one side of my bench grinder. Various buffing compounds are also available and necessary. You will need a finishing compound for acrylic or plastic. Once you have the wheel at full speed, apply the compound to the wheel until it has a good coat on it. GENTLY and at a consistent speed, run the area of the plexi to be polished across the wheel until the cloudiness fades into a crystal clear glass look. If the plexi turns white you are pushing too hard, and the friction from the wheel is melting the plexi. At this point, repeat the sanding procedure and start polishing again. It takes very little pressure to achieve a high gloss, but you MUST sand it first to at least 1200 grit unless you want to stand at the polishing wheel all day. Also, use the area of the wheel that is moving away from you. If your piece of plexi has a sharp corner, or if you push too hard, it will jerk it out of your hands, and it is better that it pull it away from you rather than throwing it at you. If you are buffing out a scratch on a flat surface, you will notice buff marks when you hold it to the light. These can be removed with a torch. Pass the torch quickly back and forth over the buff marks until they disappear.
I hope I have covered everything, I am getting pretty good with this, but I am not a professional. If you have any questions, I will be glad to answer them in the forum. Hope this information is of some value to you. Good luck!
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