posted on January 26, 2012 00:00
C.A.D. - Cardboard Aided Design
(for Dum-Dums, Cheapskates and Fifth Graders)
By Dan Barnes
Several years ago, I had an epiphany when I walked into a race shop and saw the interior tin work of an under-construction Rolex GT car mocked up entirely in white illustration board, clecos and blue tape. I made a mental note: I can do that! I can even afford that! Well, I can at least afford some illustration board and a few clecos.
|Fast forward a few years, and I had installed a Volvo 760 Turbo intercooler and radiator in the front of my turbo Miata project. The only problem was that the stock radiator shrouds didn't fit the new heat exchanger stack at all, and there were massive gaps around the radiator instead of the medium-sized ones with the stock setup.
Intercoolers and radiators only cool if there's air moving through them. Even with a stock radiator, just sealing the gaps around it so all the air that comes in the front of the car has to go through it can make a huge difference on track. Having these stupendously awesome Volvo parts just hanging out in the space in front of the Miata's engine was a problem.
Coroplast is a perfect material for radiator ducting. Lightweight and durable, easy to cut with a utility knife, and unlike aluminum or carbon fiber, if it gets bumped, bent or crushed, it springs back to its original shape. You can make designs that have to be flexed substantially during the installation process, without them ending up tweaked once installed. Since it was July, rather than election night in Little Saigon, I didn't have an infinite supply of the stuff and I needed to get this right the first time. A quick trip to the memory ATM cashed out the Rolex GT car.
Illustration board of appropriate thickness and strength proved surprisingly hard to find. Michael's, Wal-Mart, Target, etc. had thick paper and foam core, but nothing in between. I eventually found the right stuff at Office Depot, but it cost entire dollars, several of them, for a pack of four sheets. And it's all the way over at Office Depot. Fortunately, I eat a lot of cereal, which meant a 100-percent post-consumer, recycled solution was in a bin in the back yard. Corn Chex, Special K, Raisin Bran. All for free-fitty-free.
|On the Miata, I realized that I could make shroud pieces that keyed to the car, so they sealed well and were retained securely with no fasteners. As long as the radiator is in position, they can't move. But they had to be the right shape, which is complex and would be really hard to measure. These cardboard templates, on the other hand, were pretty easy to make.
Cutting cereal boxes to fit in complex spaces is an iterative process. Hold it up next to where you want it to go, mark some basic dimensions and cut. Stick it back in position, mark again, cut again. Sometimes, actual measuring with a ruler is even helpful. As the design evolves, if you find you need to add some material back or shift the position of some detail, there's no need to start over. Just find the piece you cut off of that spot, tape it back on and trim it again. In a few hours, my Corn Chex and Raisin Bran radiator shrouds for left, right and below the intercooler and radiator fit just right. Any air that entered the front of the car would have no choice but to cool something on its way through.
|I transferred the shroud shapes to coroplast by tracing the cereal box templates with a fine-tipped Sharpie. The best way to cut the coroplast is with a straightedge and knife, so it's not crushed.
Thursday, January 26, 2012 8:44 AM
Too funny...I am a huge advocate of cardboard templates for EVERYTHING. Especially helpful when working with expensive materials or when making duplicates.
Thursday, January 26, 2012 10:20 AM
Thank you for informing people about what professionals already know. CAD technology is great.
I know this isn't the purpose of the article, but corrugated material is deceptively strong especially along the the corrugates. (is that the right word?) I had to design a corrugated cardboard chair in college that could support my body weight. I weigh about 235lbs and it held great. I even tested it with my girlfriend in my lap.
And coroplast is even stronger and has better strength off axis of the corrugates than stupid cardboard. Good article, I might have to try this.
Thursday, January 26, 2012 10:22 AM
Nice article! I am sure it comes as no surprise to anyone that I am a big C.A.D. user. I also like making parts using the C.L.P. (cardboard loss process). With C.L.P. one molds fiberglass over the cardboard template. Once the resin has cured one soaks the part in water to remove the cardboard, leaving behind ready to fit part!
Thursday, January 26, 2012 11:00 AM
I've been using corrugated cardboard as a template for bending "tubes" for my scale micro crawlers. They come in real handy when you're fabbing your own bumpers or roll cages in 1/24 scale. Do all the measurements on the emplate and then just bend the styrene to fit. When we used to do an aluminum body in SAE, we would use cardboard templates to mock up the panels, then cut them out on the sheet metal. Definitely helps the trial and error process.
How temperature resistant is coroplast? I've been meaning to make shrouds for my radiator and intercooler, but I'm a little worried of it melting. My water temps have been known to hit 230 and I don't want to be scraping off melted plastic while my car cools.
Thursday, January 26, 2012 11:46 AM
According to this:
Coroplast melts at 324*, plenty for the radiator. It might get a little flimsy when especially hot, but the absolute worst case is the spot where it touches the radiator deforms a little.
Thursday, January 26, 2012 12:19 PM
I just used C.A.D. to fabricate a custom intercooler duct. Works great.
Thursday, January 26, 2012 7:43 PM
something I use is chipboard. you can buy it in a variety of sizes and the price is pretty reasonable for how much you can get. I normally buy from Uline but we order boxes from them all the time. http://www.uline.com/BL_1852/Chipboard-Pads?Pricode=wj374&gclid=CIG46Z6J760CFahgTAodt31itQ
Thursday, January 26, 2012 11:45 PM
@Alex, I hadn't thought of the CLP process before. A similar strategy I remember from my model airplane days is to use polystyrene foam to shape the plug. After you glass it, melt the foam out with a solvent such as acetone or gas. Probably better for making complex/compound curved shapes than cardboard, if that matters. Hadn't thought of that in awhile. Might need to try it on something soon.
Thursday, January 26, 2012 11:58 PM
Hell man, a cardboard chair isn't even pushing it. We designed and built full-size, one-man cardboard BOATS in my senior year of high-school and then raced them around the pool! Ours was a simple canoe-type design and it held up so well that one of my team partners took it home to float around on his grandparent's pond. He even went fishing in it a couple of times.
Thursday, February 02, 2012 10:09 AM
I like that foam loss method and it works well for more 3D shapes. One had to use epoxy resin as the polyester will melt the foam and then there are tears. Glassing over cardboard is a just jiffy way to make a flat or simple curved part in a one off situation.
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