From: Torsten.Lif@eos.ericsson.se (Torsten Lif) Date: Tue, 26 Jan 93 17:33:29 +0100 Subject: Bending acrylic Aha, a cue to move to another subject again... One of the few remaining features I've not yet been able to get on my 'bent but that I was used to on my upright is a map holder. On the upright I had a Cannondale handlebar bag with a map pocket on top. For the recumbent I had the following idea that I've not yet tried out in real life: Get a piece (about one foot square - 30 by 30 cm) of clear semi-hard plastic, bend it into a cylinder and attach to the frame in front of the seat (probably in front of the cyclometer too). Roll up the map and stuff inside. You only see a strip about 3 - 4" wide of the map but I think that should do - the plastic pocket on the Cannondale bag was only about 4" high and an older map holder I had worked by putting a rolled-up map of about that same size on top of a handlebar bag. (Of course, these two placed the strip of map *across* your field of vision while my cylinder would sit *along* the frame. Does that matter?) You'd have to be careful not to introduce any health hazards in case you crash and sit town on the frame, but I suspect the plastic will break away before you get seriously injured. So how do I bend acrylic ("plexiglas") into a nice cylinder)? If I first do a crude job to merely "fold" it far enough that the edges overlap, can I then re-heat it to have it "spring out" to become nicely cylindrical or will it just collapse into a heap of Jello? /Torsten From: "Nickolas E. Hein" Date: Tue, 26 Jan 93 11:33:41 PST Subject: Re: Bending acrylic You may want to avoid using acrylic. Polycarbonate (trade name Lexan) is far more flexible tougher. It also doesn't fade or haze with age. Any plastics supplier usually carries it. In our area we have a surplus store that (last time I checked) had clear tubes of the stuff which sound like they might meet your specs. Let me know if you'd like me to check further on it. Sounds like a really useful idea. Nick -- I take responsibility for everything I say, that's my problem. But I could be completely wrong, that's your problem. ============================================================================= Nickolas Hein | Voice: (206) 662-4972 Boeing Commercial Airplane Group | Boeing net: neh3568@aw101.iasl.ca.boeing.com P.O. Box 3707, M/S 19-MK | Snail Mail: 12829 SE 184th st Seattle, WA 98124-2207 | Renton WA 98058 ============================================================================= From: bleep@ux1.cso.uiuc.edu Date: Wed, 10 Mar 93 17:18:27 CST Subject: fairings and acrylic bending, again! There nothing like beating, kicking, gouging, slaming and otherwise just in general making a dead horse uncomfortable, so here it goes: Has anyone try using a vacuum pump and a wood mold in combination with a heat blanket to bend compound curves from thin or not so thin plexigas/ polycarbonates? Commercial vacuum forming equipment is usually size limited, but I recently obtained a used hefty vacuum pump for the purpose of building a veneer press (FYI, veneer press for woodworking). If it's simple, I might try to make some fairings.... TB, Materials Science Dept. U of Illinois, C-U. bleep@ux1.cso.uiuc.edu From: mason@asylum.sf.ca.us (Latte' Jed) Date: Wed, 10 Mar 93 20:29:19 -0500 (EST) Subject: Re: fairings and acrylic bending, again! I've tried forming plexiglass by vacuuming it into a mold in a large oven. I couldn't get it to deform evenly, it wound up lumpy. So there's at least some amount of technique involved. From: Mike Bonham Date: Thu, 11 Mar 93 10:15:12 MST Subject: Re: fairings and acrylic bending, again! TB, bleep@ux1.cso.uiuc.edu says: > Has anyone try using a vacuum pump and a wood mold in combination with a > heat blanket to bend compound curves from thin or not so thin plexigas/ > polycarbonates? Sorry, no! > ... I recently > obtained a used hefty vacuum pump for the purpose of building a veneer > press (FYI, veneer press for woodworking). If it's simple, I might try to > make some fairings.... Hey what a great idea... forget about moulded plastic fairings... make a cherrywood veneer thin-plywood body shell for your cycle! What a beauty that machine would be! Can you mould plywood into compound curves with a veneer press? Then, to protect the finish, I suppose one would want to overlay the veneer with a shell of moulded polycarbonate plastic :-) -- Mike Bonham Jade Simulations International bonham@jade.ab.ca From: bleep@ux1.cso.uiuc.edu Date: Thu, 11 Mar 93 19:22:10 CST Subject: Re: fairings and acrylic bending, again! >from bonham@jade.ab.ca: >Hey what a great idea... forget about moulded plastic fairings... make a >cherrywood veneer thin-plywood body shell for your cycle! What a beauty >that machine would be! Can you mould plywood into compound curves with >a veneer press? Well...(I'm assuming you're serious in your question) you can -make- (don't have to buy and mould) your own plywood using a vacuum veneer press and loose veneers. It's a simple process, just add one layer on top of another until you get the desired thickness. The piece will hold its curvature after removal. Now that you mention it, it's also possible to "inlay" a polycarb window inside such a fairing. The main problem for using the vac. ven. press to bend plastic is that the veneer press uses a plastic bag around the whole set up (to contain the vacuum), so you can't apply any heat, or the bag will melt. This problem is why I posted the question orginally. I've read that vvp's that have heat blankets are available...but I'm building my set up, not buying it. The commercial ones are EXPENSIVE! 1k+ us $, I think. Veneers ain't cheap, though. You can make your own if you have a bandsaw. Tho "Dammit Jim, I'm a woodworker, not a bicyclist!" Bui. From: bwilson@zippy.sonoma.EDU (Brian Wilson) Date: Thu, 11 Mar 93 17:30:29 PST Subject: Re: fairings and acrylic bending, again! Resent message from ianf@random.se follows. ------------------------------------------------------------------------------- > > Latte' Jed writes: > >> I've tried forming plexiglass by vacuuming it into a mold in a >> large oven. I couldn't get it to deform evenly, it wound up >> lumpy. So there's at least some amount of technique involved. > > As someone with fair amount of vacuum-forming experience on my > conscience (albeit not of fairings) I can vouch for the > difficulties involved in achieving passable results. > > Generally speaking thermoforming of acrylic and/ or polycarbo- > nate sheets (trade names Plexiglas and Macrolon/ Lexan) over 1 > mm in thickness require _very_even_ preheating, **lots** of > vacuum or evenly-applied air-pressure AND plenty of preparations > to succeed. > > I'd imagine that hand-forming of sheets of circa 0.5 m2 or > larger (i.e. suitable size for a recumbent fairing) might be > doomed to fail anyway... sheets that big require professional > machinery or else. Therefore, should anyone feel like doing it, > it might pay to preheat the sheet well and then simply bend it > along the diagonal (single-axis) mechanically and cool down in > that state by submerging in a tub of water or equivalent. > > Were I to attempt making a real (convex) thermoformed fairing > I'd start by constructing a semi-professional preheat/vaccuum > table, made out of a number of infrared heating elements, spaced > 10 cm apart and backed up by aluminum sheet, suspended in a > moving frame. Make sure that the area covered by it is larger > than the acrylic by 10-20 cm in each direction. > > _____________________________________________ <-- heat reflector (a) > o o o o o o o o o o o <-- IR-elements (b) > []-----------------------------------------[] <-- sheet of acrylic (c) > +===== - - - - - - - - - - - - - - - - =====+ <-- table w/ cutout (d) > | | > | | > | | <-- vacuum chamber (e) > | | > +-----+ +------------+ +-------------+ +----+ > | | | | | | > | +------------+ +-------------+ +----- <-- to vacuum pump (f) > +-------------------------------------- > >(a) use fibreboard covered with mineral insulator and aluminum > sheet right above the IR-elements >(b) [shown in profile] move the (a)--(b) constantly during the > warming up to ensure even spread of heat >(c) acrylic must be clamped tight in a wooden frame; make sure > there's a tight fit between frame and edges of (d) >(d) the cutout should be in the form of "elongated egg-elipse" ;-)) > placed diagonally never closer than 10 cm to any edge >(e) vacuum chamber should be made out of 1" plywood or similar; > 30-40 cm deep >(f) a 1.0--1.2 mm acrylic sheet, 80*80 cm (= enough for a small > fairing placed diagonally across it) might need as much > vacuum as that generated by 1 industrial-size vacuum cleaner > (2000W output) or 2 domestic ones. Use 1 inlet per 12-16 decim2 > > Mind you, it still might be cheaper to have it done professionally. > Try art/ design colleges specializing in stage design since they > might have vacuum equiplemnt that's big enough for fairings. > > >__Ian "never mind thermoforming, I rshould be be vacuuming now" || Brian Wilson || Computer and Information Science Dept || Sonoma State University, Rohnert Park, California || 707-664-2182 From: bleep@ux1.cso.uiuc.edu Date: Thu, 11 Mar 93 20:36:07 CST Subject: Re: fairings and acrylic bending, again! After reading Brian's note, I decide to add some more details about the veneer vacuum press in case some one has a clever use for it. the VVP (my acronym) is a recently developed (marketed?) tool for wood workers. Its working principle is simple: Put your mold and object+veneer into a big bag, and pump out the air. The atmospheric air pressure will supply 14.7 pound for each square inch of the surface. The need for holes in the mold is not necessary. Now, my artistic skill: ooooooooooooooo ooooo ooooooo ooo ooooooo ooooo ooooo o oo o vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv o o ooooooo o wwww wwwwww vacuum o wwwwwwwwww wwwwwwwwwwww out----> o wwwwwwwwwwwwwwwwwwwwwwwwwwwwwww ooooooo o wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww o oooo oooo ooooo oooo oooooooooo ooooooo ooooooooooooooo v is the veneer, w is the wood (or mold), and o is the bag. Commercial model, as I mentioned on a previous note has optional heating blanket--how much heat, I dont know. Whether 14.7 psi is sufficient to deform a softened piece of plexiglass, I don't know either (it should, intuitively). As you can see, the design is pretty elegant in its simplicity. The amount of vacuum power isn't as great as with the case of vacuforming, and the mold can be polished to a mirror finish. Commercial models are (oh God, memory's failing) about 3-4 hundred bucks for something that will handle a good size desk. The quality (thickness) of the bag is better for the more expensive model. Some woodworker magazine has plans for making these presses using thinner, but widely available plastic sheets in hardware store...Tape the seam carefully, etc Uses other than non woodworking? I suppose you can use it to mass produce fiber/epoxy shells with proper protection from the glue. ...What do you think? useful for hpv'ers? Tho "building chairs is easier than building bikes" Bui. P.S. For those of you who dabble in both, I just made a mountain bike handle bar out of ash (baseball bat wood). It weighs 162 grams. Kinda springy (shock absorbing) too. Who needs titanium :-) ? From: R.Stclair@EBay.Sun.COM (R D St.Clair) Date: Fri, 12 Mar 93 09:04:52 PST Subject: Re: fairings and acrylic bending, again! For more information on variations of the vacume bag technique, check with your local hobby shop. They have been using this technique for years to make extremely strong and light weight wings. Sometimes it is as simple as veneer over a foam core, but they also do more exotic things like carbon fiber and glass composite layups with seperator sheets and felt pads to soak up the excess epoxy. This creates an extremely high glass (carbon) to epoxy ratio which is just what you want for maximum strength and minimum wieght. Obviously these kind of parts are not clear, and are more structural in nature, but there are many uses for such a process in Bent construction. Not just fairings, but possibly the whole bike. P.S. 14 P.S.I. produces a fantastic amount of pressure over any fairly large surface. You can't begin to equal it by simply pushing on things with normal human strength. Thanks, R.D.