| Author | Message | ||
     Torquehd |
Today's random DIY engineering question - When I get around to it, I plan on making my own windscreen and other clear "plastic" pieces for my 1125. I've read all about vacuum forming, seems like "cake" (after you get the trial/error out of the way). I've also read that polycarbonate is the material of choice. Will any ol' polycarbonate work, or does it need to be automotive-grade stuff? The reason I ask is that I haven't been able to find "automotive grade" poly. I'm also curious if plain-jane polycarbonate will maintain crystal-clarity after forming (not looking all warped and stretched). Any other/better materials? | ||
| Sifo |
Just be aware that the stuff you typically find at the hardware store is not polycarbonate, but usually acrylic. It's another one of those projects I've looked at and have backed off from. Polycarbonate is probably the best material for this project. One thing that put me off of the project is that the typical mass-produced windscreen had a hard protective coating that provided durability. I'm not sure if that's done before or after forming, but I don't think that's a DIY step. I just wasn't convinced I would get the durability of the finish I wanted. Perhaps the "automotive grade" has this layer applied. Might want to ask the manufacturer, or seller. | ||
| Etennuly |
I built a BAW for my Uly out of polycarbonite. I got a 4'x 10' sheet from a manufacturer for some stuff I was doing for a customer. Polycarbonite is not shatter proof, it will break into large pieces on hard impact. It will not heat form from a sheet. I tried many methods finding that it will curve to a frame but will not fit to a form. I think the polycarbonite windshields you see are mold formed. I am not sure what processes they use though. Lexan is a good product that can be formed, but it is rather limp structure wise. | ||
| Mnscrounger |
Lexan is the GE Plastics trade name for polycarbonate plastic. another common name is Makrolon. It can be thermo, and vacuum formed under heat. Glass transition temp as I recall is about 220F The problem is if it is heated too quickly or too high, moisture trapped in the plastic boils and creates bubbles that cloud the plastic. I made a taller windshield for my Suzuki using a cut down surplus NOS snowmobile windshield. If you can leave it in a form over time, it will take a modest "set" to the contour, but you need to exaggerate the form to end up where you want. If you use a heat gun you need to heat uniformly and gently or you get all kinds of ripples and bubbles. The result was OK,(my Suzuki could get away with homemade)  When I wanted a taller windscreen for my S3, I opted to pay good money for a professionally made one from Zero Gravity (acrylic I believe) A nice looking bike like an 1125 deserves a nice looking screen. If you get a group here to agree on a design and commit to buy enough, I'll bet ZG, Rifle, or Gustaffson will make them for you. | ||
| Aesquire |
Polycarbonate works nice, but scratches easy. I suggest heating it in an oven set to 200F and draping it to the shape desired, Then trim to fit. Single axis bends are easy. Multi-axis bends are harder, and need more heat to make the material more plastic. When you get into vacuum forming temperature control gets more critical, as does smoothness of surface in the mold. Plexiglass ( reg trademark )is even easier to work and has less foibles than polycarbonate, but less impact resistance after molding. Still good enough for most applications. I've seem Plexiglass overheated into a wrinkled mass, tossed back in to be re heated, and work just fine. Polycarbonate ( lexan ) will do the cloudy thing, as Mnscrounger points out, and even foam if you overheat it. I knew a guy who was experimenting with polycarbonate for body armor, and actually wanted it to foam but was unable to hold the temps at the critical point while shaping it. If you want the numbers for melt points, and flows....I have a bud who is a pro injection mold guy, but I have done more oven work over the years. #1 tip. be ready to scrap & start over. It's a learning experience. #0 tip, don't leave plastic in the oven unattended unless the better half is out of town for at least a week, and you can afford to buy a new oven before she gets home. DAMHIK. I haven't done a lot of work in Acrylic, but have in ABS, ( opaque ) and find it very easy to shape by hand with gloves out of the oven. | ||
| 1313 |
Lexan..can be thermo, and vacuum formed under heat...The problem is if it is heated too quickly or too high, moisture trapped in the plastic boils and creates bubbles that cloud the plastic. Thanks for the knowledge!!! That must've been the problem I encountered trying to vacuum form the headlight 'cover' for my S2. My attempt in Lexan/polycarbonate (PC) was definitely not optically clear with lots of little bubbles. Using the same equipment, a piece of acrylic produced what I was after without any issues. A 'note' about acrylic vs. Lexan/PC - FWIW... Early S2 windscreens were acrylic, which could leave sharp jagged edges upon failure. Buell was forced to change the S2 windscreen to Lexan/PC to limit the liability if someone got tossed over the bars - as with a Lexan windscreen they wouldn't get impaled on the windscreen. I still have an acrylic windscreen on my S2 to this day... In Orlando it was interesting to see the same manufacturer logo on the 1190RX windscreen as were on the Lexan/PC S2 windscreens, 1313 | ||
| Torquehd |
Thanks for the thoughts men. here in a few weeks when I get back to the house, I'll start playing around and let you know what I find out. There's got to be some halfway practical solution for the DIY'er. | ||
| Mr_grumpy |
I just wander round the recycling point or the junk yard with forms & ideas in mind & look for stuff I can adapt. Works for lots of things but drives my wife mad. | ||
| Torquehd |
It looks like the problem with polycarbonates is moisture content (will have to dry in oven at 200F), and that they often cool too quickly. I might try preheating the mold, and possibly covering the sheet with pre-heated insulation to help with that. I've also read that covering the mold face with felt will help prevent premature vacuum seal before conformity is complete. PET-G seems to have decent impact resistance and is one of the easier plastics to form, i might try that for headlight and taillight lenses. PETG vs Polycarbonate and ABS: http://www.youtube.com/watch?v=EqUyCbfn5Og Polycarbonate vs acrylic: http://www.youtube.com/watch?v=juGAndzfFkM (Message edited by torquehd on October 29, 2013) | ||
| Torquehd |
After more google-based research, the protective coating used by auto manufacturers is typically a UV and abrasion resistant coating. There are a plethora of companies that offer these coatings and they can be solvent based, air-cured, UV-cured, thermo cured, etc. I emailed half a dozen companies inquiring about getting a small quantity to test. I'll have to wait and see where it goes from here. | ||
| Mnscrounger |
PETG has good impact resistance, and forms really well. Being polyester it should act like polycarb when you exceed the properties. (meaning I think it would tear like polycarb, Unlike acrylic which tends to crack.)What I dont know about,(among a million other things) is how it holds up in cold weather, and how UV stable it is. DISCLAIMER: I am NOT an Engineer, My limited knowledge of plastics is worth exactly what you pay for it.} | ||
| Torquehd |
PETG is my backup plan (i mean the stuff likes like complete cake to vacuum form and is still just plain stout), and since none of the hard coat manufacturers have gotten back with me, I'll probably try clear coating it with a UV stable clear-coat with hardener. Sorry for all the talk with no action yet, i'll be back home in a couple weeks and then it'll be time to start tinkering. | ||
| Sifo |
I'll probably try clear coating it with a UV stable clear-coat with hardener. I had a wind screen that was damaged. I was modifying it for another bike. Wound up sanding the coating off because of the previous damage, sanded to 1500 grit hoping the clear coat will fill in and become invisible like it does when you paint over sanded paint. Very disappointing. I may spend some time this winter trying to polish it clear again. If I get that done to my satisfaction, I will try the clear coat again. | ||
| Aesquire |
http://www.lpaero.com/CAREINS.pdf Another word of caution. If you are working on a homebuilt with polycarbonate, or “Lexan,” windows, there is no good way to remove scratches. Polycarbonate is so soft that any attempt to remove material by abrasion will do more harm that good. There are hard coated varieties of polycarbonate that are less scratchable, but trying to repair a scratch in these will only remove the hard coating. Your only option will be to fill minor scratches with a scratch-filling polish or replace the window. There is a kind of special sand paper that is designed for polishing/smoothing plastic windscreens. Instead of a bunch of randomly oriented rocks glued to paper, it has oriented, plane like rocks glued on. It acts like multiple tiny planes, instead of random pointy cutting tools. Can't find the brand name on first pass through Google, When I find it I'll post it. The link above has some comments on polishing and scratch removal on various plastics. Since most aircraft windscreens are molded or bent plastic, there's lots of articles on scratch fixes in magazines, like Kitplanes or Flying. Haven't tried this one, but it's worth noticing the range of "mesh grit" from 1500 to 6000 in a well reviewed kit. http://www.skygeek.com/hp-100.html I've used Mothers plastic polish for headlights by hand, and while tedious, it works. I'll buy the powerball version next time, but I'm also well aware how fast power tools can ruin your day. http://www.mothers.com/02_products/07250_c.html For helmet visors I'm now a total Plexus and rag kind of guy. |
