Working with Sintra®1 A different kind of PVC -- 14 July, 2002 The basics Adhesives Fasteners Finishing & Conclusions The basics -- what it is, where to get it, how to shape it A fairly old material has recently found a new life in BEAM robotics. Sintra® is the brand name for Alusuise Composites' rigid PVC (poly vinyl chloride) foam board2, a moderately expanded, closed-cell PVC sheet. Developed in Europe in the 1970's, Sintra® was introduced to North America in 1980, and has been used primarily in signs and displays to date. Thanks to a number of useful properties, though, Sintra® and its cousins are seeing increasing attention of late from robot builders. Sintra® is available in thicknesses from 1mm to 19mm (but 3mm and 6mm are the most common), and a dozen colors (white is available in all thicknesses, the other colors just in 3mm and 6mm; more about colors later). As a result of its structure, Sintra® has a number of properties useful to BEAMers: High stiffness Light weight -- half the weight of solid PVC in gauges of 1 - 6mm, slightly over one third the weight of solid PVC in 10mm and thicker gauges Resistance to moisture and many chemicals Smooth solid faces -- just the ticket for ease of finishing, as well as resistance to grime buildup Easy to work with (but more on this below) Where to get some Sintra® and its cousins can be found with varying degrees of ease locally. Since BEAMbots won't require very large pieces, you can sometimes find what you need in sign shops or at plastic distributors (ask them if they have any scrap bins; on rare occasion, you can even find a place that gives away their scraps for the taking). Of course, when it comes to scrounging, you'll be at the mercy of local conditions and dumb luck as to the availability of different thicknesses and colors of material. Most likely you'll need to break down and actually buy material -- here, there are a couple of ways to go. Sintra® and its cousins leave the factory in sheets 4' x 8' and larger, so if you need a bigger piece than you can find in local scrap bins, but don't want to buy (much less pay shipping on) a full sheet, you'll have to work through a distributor. U.S. Plastic Corp. will sell you a quarter sheet (2' x 4') or half sheet (4' x 4') of Sintra® in your choice of many thicknesses and colors. Most likely, though, you'll want a still smaller piece than that. Both Solarbotics (with Sintra® in a variety of colors and three thicknesses) and Lynxmotion (stocking two thicknesses, in any color you like -- so long as you like yellow) will sell you 8" x 12" pieces. Cutting, machining, and forming Sintra® can be shaped much like wood. Pieces up to 3mm thick can be cut with a good shop knife; 6mm sheet can be scored with a knife and snapped on the score line. For speed and a very smooth edge, you can also cut Sintra® with a circular saw, table saw, band saw, or router. After you're done cutting, you can smooth any rough edges with a file, or with medium grit sandpaper. Thanks to a few Star Wars fan sites (Sintra® seems to be a big hit with the home-built costume crowd), I ran across another interesting item -- Sintra® is a thermoplastic, and starts to soften at about 150° F. This means that you can easily heat up thin (3mm or thinner) pieces of Sintra® and mold them as needed. To bend a piece of Sintra®, you just boil it in water for 10 - 15 seconds (the length of boil determining how soft the material gets). After boiling, remove the piece with tongs (gently, so as not to leave an imprint of the tong in the piece), quickly bend it to your desired shape, and freeze it in shape with cold water. If you mess up, it's no problem -- keep your water boiling, and you can just repeat the process. For what it's worth, you can bend thicker pieces of Sintra® as well, although boiling water probably isn't hot enough to do the trick. Hello, Dali!   Sintra® brings a whole new flexibility to BEAM bot design As a note of warning, be careful not to crush Sintra® while you're manhandling it -- crushing destroys the material's internal cell structure, leaving you with a very flexible and essentially useless mess.   Sticking pieces together When the time comes to put pieces of Sintra® together in a durable way, you have two paths you can follow -- namely, the use of adhesives and / or fasteners. I'll discuss fasteners in a bit; as for adhesives, well that's the subject of the next page. Notes: 1. Other vendors produce products comparable to Sintra®; these are sold under the brand names of Kömatex® (by Kömmerling), and Celtec® (by Vycom). Thanks to Sintra®'s market dominance, though, it's the brand name you'll most often run across, and is often (if inaccurately) used as a generic term for PVC foam board. 2. Note that when you're shopping for PVC foam board, you need to make sure you are not getting Fome-Cor®, a.k.a. "foam core," which is much softer, and essentially just paper-faced styrofoam. 3. For those who may need such information, I've hosted a zipped copy of the SINTRA material safety data sheet (MSDS) here. The basics Adhesives Fasteners Finishing & Conclusions

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