Guest TeamNissan Posted February 16, 2008 Share Posted February 16, 2008 I like vac forming for complex shapes but I think slumping is such a cake walk its better suited for personal app. Windows, cowls etc.. vac forming is over kill imo. I mean for a mold or to make a run vac forming makes sense but for one off to me it doesn't, slump it, sand it, polish it.... Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted February 16, 2008 Author Share Posted February 16, 2008 Copied from http://www.acrylic-designs.com/plastic_FAQ's.htm I underlined part of it... Andrea writes, Hi I'm trying to bend a thin sheet of acrylic into a wavy shape at home any suggestions on how to do this? First of all let me give you little background on forming plastics in general. As acrylic plastic heats, it shrinks. approximately 1/4 of an inch per foot in cast acrylic. Extruded acrylic shrinks one way and can expand the other. You should test a piece if length is critical or be prepared trim the length after forming. Acrylic plastic becomes flexible at around 280 degrees. You should set your oven at 350 to 400 degrees. It will take 2 to 8 minutes to heat depending on actual temperature, thickness of material and what you place the plastic on to heat. If you need to have an exact shape for the part you want you will need to create a form or mold. This can be any smooth surface. I have used glasses, bowls, cups, aluminum cans, about anything I have laying around that can be close to the shape I want. We use Formica pieces, cardboard tubes or any firm flexible surface to make larger curved parts. Sometimes, with small pieces, you can just use gloves to hold it. Another important thing to remember is that when the sheet is flexible, it will get "mark off" from any surface it comes into contact with. We use cotton flannel to cover the surface of our form. Glass is often smooth enough by itself. Dust particles will leave imprints. The plastic should be put into the oven on a piece of smooth hardboard, Formica, or cardboard. Corrugated cardboard will not burn at these temperatures in 15 minutes. Keep it away from elements or flame and don't put it in until the oven is hot. Use reasonable caution. I have used aluminum foil in a pinch but it tends to stick. You can take the plastic out of the oven on the board, or carefully cradle it out with gloves. It will be hot so gloves need to be worn. You can get a cheep $3.00 to $5.00 pair of leather gloves at a hardware store. Try not to grab it with your fingers as you will leave imprints. Quote Link to comment Share on other sites More sharing options...
ihatejoefitz Posted February 16, 2008 Share Posted February 16, 2008 My dad has a couple vacu forms at his work. I always thought making a sort of "clamshell" two piece intake manifold that could be sonic welded together would be awesome. But because of the precision needed, I think plastic injection molding would be better suited. Quote Link to comment Share on other sites More sharing options...
Tony D Posted February 18, 2008 Share Posted February 18, 2008 Vacuum forming gives great detail but for your Ferrari inspiration and using thicker materials do a Google search on drape forming. Simplier shapes but you can create inexpensive wood male molds, heat your clear sheet material and drape form it over your mold to create your part. I have to agree, if you search my posts, drape forming is what I used to do windows a long time ago. I think I even described the 'oven' I made using several heat guns and an old electric oven thermostat. Get it all evenly heated, pick it up with tongs and gingerly drape it over you buck, if you get frisky, have an oversized 'die' to lay over it that will hold it tight to the form while it cools. Then trim and start over on another piece. I had the chance to pick up a vacuum forming setup from a friend, but wasn't interested at that time. It would have been good for parts, it was for making bubbletop skylights for vans (groovy, man!) and was about the right size for headlight covers. Though with some two-piece molds/bucks you might be able to drape it over a buck and press the B section over and make a passable headlight cover...cosmetically at least. I would still think vacuum forming would be the way to go there. Then again low pressure could work the same way to press the piece over a positive buck...pressure is only a relative thing when discussing vacuum.... Quote Link to comment Share on other sites More sharing options...
Challenger Posted February 18, 2008 Share Posted February 18, 2008 They make clear plastic engine parts for dirtbikes. I guess the y jus fog up really quick. Id like to see a lexan/clear plastic intake manifold. That would be cool. Me and my granpa used to make wooden airplanes and wed use the oven to form clear plastic to make the cockpit windows. Turned out good, and was quite easy. Quote Link to comment Share on other sites More sharing options...
G.I.jonas Posted February 18, 2008 Share Posted February 18, 2008 OTM if you need a vacuum pump i do have a nice one that i may be willing to part with. Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted February 18, 2008 Author Share Posted February 18, 2008 Gijonas, That is really cool. I'm in the middle of buying a couple cars (LOW vin series 1) and dumping one so I might be ready to do some plastic forming in a few weeks. Quote Link to comment Share on other sites More sharing options...
Shift Posted February 19, 2008 Share Posted February 19, 2008 You can make a vac forming rig from a couple old toasters. a bench some wood and a shopvac. For the forms. you can shape the approximate shape with foam then cover and shape with bondo. cheap and easy, and the bondo make a smooth enough surface to help keep the acrylic clear. Quote Link to comment Share on other sites More sharing options...
Tony D Posted February 19, 2008 Share Posted February 19, 2008 Yes, I second the ShopVac idea. It will work nicely to either blow low pressure onto the top, or evacuate the area under the form to make the hot drape fit fast and tightly. Especially that 16HP bugger Home Depot is selling (Emerson Electric Plant shut down, so I don't know where it's made now but it was in the town I grew up in: Menominee, Michigan...which also has Coleman Racing Products...hmmmm, maybe I should move back...) Quote Link to comment Share on other sites More sharing options...
Some-Guy Posted February 20, 2008 Share Posted February 20, 2008 heres a cheap vacuum forming unit a guy I used to know made. served him well looks pretty easy to make too! http://cnc-g-spot.com/MSEvacuform/K-Martha%20Vacuformer.htm Quote Link to comment Share on other sites More sharing options...
mull Posted February 20, 2008 Share Posted February 20, 2008 Who'll be the first to make a clear plastic dash? Quote Link to comment Share on other sites More sharing options...
bjhines Posted February 20, 2008 Share Posted February 20, 2008 I have been looking into some of this as well. Back in the day I worked with a high end car installer. I was in another part of the shop, but I spent a lot of time in the install garage to see how these guys did their work. They used a couple of guys and some propane torches to make really nice bends on straight lines. They also used the torches to smooth out and clarify the cut edges. They were not doing anything but bending the sheets like they were bending sheet metal on a brake. The bends looked great. The material was sometimes 1/2" thick. Quote Link to comment Share on other sites More sharing options...
Wedge Posted February 20, 2008 Share Posted February 20, 2008 Who'll be the first to make a clear plastic dash? Lol i was thinking the same hehe Quote Link to comment Share on other sites More sharing options...
jknc90 Posted February 21, 2008 Share Posted February 21, 2008 I'd like to see a clear valve cover. I think it would be awesome to be able to see everything inside while the car's running. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted February 21, 2008 Share Posted February 21, 2008 Years ago, I looked into this extensively being I wanted Lexan headlight covers for the BlueovalZ because the normal Z covers would not work. I found (and haven't seen it mentioned yet) is that air bubbles can form in the plastic if not warmed slowly and evenly and allowed to stay at temperature for a short period. I've not seen reference to this as yet, but I seem to remember something about electric ovens being a great deal better than a gas oven in reducing the bubbles as well. Quote Link to comment Share on other sites More sharing options...
Tony D Posted February 21, 2008 Share Posted February 21, 2008 Er, yeah... the damned bubbles. It also depends a great deal on who makes your plastic as well. "Slow and steady" is a good rule of thumb. I would set the 'oven' to 140 and get it there, stick the sheet in, put the cover on, and then raise the temperature from there to 325 in varying steps. My first attempt at just blasting six heat guns into a box with the thermostat set at 300 degrees had...er...'less than desirable effects'... ahh the impetuous rush of youth. I learned that 140, 225, 250,275,300,325 and then getting all set makes for a nice 'droopy' sheet that you can pick and fling pretty nicely. If you have a cold breeze, or a cold garage, you may want to bring the heat up another 25 degrees to 350. Some of the stuff drapes nice right at 300, other stuff likes it hotter. There is a 'feel' you will get when you do a few. if it's complex forming, and not just dropping it over a relatively flat window buck, I'd err on the side of 'hot' to make sure it drapes and you can form it (like stated with cotton gloves) while it's still hot...it will harden right there before your eyes. Get it too hot, and your gloves stick into it, you scream as hot plastic sticks to your flesh as you realize the cheap gloves your buddy gave you were nylon and not cotton... I digress, but I'd encourage anybody to try it. The cost is pretty low, and the stuff you can do is pretty amazing. I would say I will do it again when I get some time. Burnt fingers and all, the stuff you can make is pretty cool! Quote Link to comment Share on other sites More sharing options...
Shift Posted February 23, 2008 Share Posted February 23, 2008 I have been looking into some of this as well. Back in the day I worked with a high end car installer. I was in another part of the shop, but I spent a lot of time in the install garage to see how these guys did their work. They used a couple of guys and some propane torches to make really nice bends on straight lines. They also used the torches to smooth out and clarify the cut edges. They were not doing anything but bending the sheets like they were bending sheet metal on a brake. The bends looked great. The material was sometimes 1/2" thick. I wouldn't advice in using a torch around acrylic, inless you are extremely skilled. acrylic starts to bubble around 250 degrees (cheap Home depot stuff and high end acrylic PC cases, and sub boxes from experience) The guys on mythbusters used a rig similar to what I mentioned above. What you are looking for as far as a heating element is concerned is chromium (or nickle chromium, I don't remember) found in toasters or other heating appliances. older the toaster the thicker the wire is. Well actually I think you might be able to get away with using a space heater. Make a frame to hold the plastic, suspend it. Heat it from the top, then lower it onto the form on top of bench with a hole cut into it for the vac. the turn on the vac. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted February 23, 2008 Share Posted February 23, 2008 My very limited understanding of the bubble issue is from water (yes, even plastics have water in them, and in my tesla coil hobby, it becomes more apparent). The use of any fuel to heat the plastic usually envolves the creation of water (gas, propane, etc), which is why I believe the electric ovens or heating elements are used for this purpose. Quote Link to comment Share on other sites More sharing options...
Shift Posted February 25, 2008 Share Posted February 25, 2008 I wouldn't advice in using a torch around acrylic, inless you are extremely skilled. acrylic starts to bubble around 250 degrees (cheap Home depot stuff and high end acrylic PC cases, and sub boxes from experience) The guys on mythbusters used a rig similar to what I mentioned above. What you are looking for as far as a heating element is concerned is chromium (or nickle chromium, I don't remember) found in toasters or other heating appliances. older the toaster the thicker the wire is. Well actually I think you might be able to get away with using a space heater. Make a frame to hold the plastic, suspend it. Heat it from the top, then lower it onto the form on top of bench with a hole cut into it for the vac. the turn on the vac. EDIT: sorry ment to type 350 degrees and thats with a torch (it will be pretty stiff still, depending on type of plastic.), if your usng a convection type heating than 450 degrees Quote Link to comment Share on other sites More sharing options...
blueovalz Posted February 25, 2008 Share Posted February 25, 2008 What I did was bought a bunch of used oven heater elements on Ebay so that they could be inclosed in an insulated metal enclosure that would be flat and wide enough to do the job. These come in such a large variety of shapes and sizes that you can make an "oven" of just about any size. Quote Link to comment Share on other sites More sharing options...
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