Miracle Recreation Equipment Company builds a broad range of park and playground equipment; you’ll probably find some in your neighborhood. Chances are you or someone you love has zoomed down one of its slides or swung in one of its swings. This is the story of one particular slide and how it got its colors.
Originally, when Miracle designed their Chameleon modular slide, the idea was to allow each Chameleon to be assembled in an assortment of colors, as befits its name.
The Chameleon consists of five rotomolded plastic sections: an entry, a straight section, a left bend, a right bend, and an exit. The pieces would be assembled to create slides of different shapes and lengths: a right turn, a zigzag, a straight slide, and so on.
But Miracle encountered a problem. Rotomolded plastic parts shrink after manufacture and, different colors have different amounts of shrinkage. Yellow parts shrink more than green parts, for example. As a result, the different colored edges warp and pull away from each other.
This meant that the Chameleon couldn’t be built from multiple colors; different colored parts didn’t fit together well enough. Rather than give customers a potentially bumpy ride, Miracle decided to limit each Chameleon to a single color. But what’s a Chameleon that can’t change color? So Miracle set about redesigning a slide that could.
Lips and grooves. “We had to come up with a new scheme to make these different colored pieces fit together,” says Olen Swaim, Miracle design engineer. With the original Chameleon design, the edges of each section were simple flat planes, butted against each other, that could easily pull apart. Swaim designed new pieces with a groove at one end, and a lip at the other. The lip fits into the groove of the next piece, a little like a tongue-in-groove joint. Swaim also tapered the ends, so they would pull into each other, eliminating any gap. The combination of lip, groove, and taper allow the pieces to be pulled snuggly together.
“We designed the parts with interference to compensate for any shrinkage,” says Miracle engineer Kathy Geyer. “After assembling the mating parts in Pro/ENGINEER, we could calculate the amount of interference using Pairs Clearance under the Model Analysis Menu. We could see the interference using Clip under the Visibilities Menu.
“The way they mate is really complicated but, even if the seams pull back when the material cools, when you bolt the pieces together, they will pull up tight and fit smoothly.”
The Miracle team didn’t eliminate the shrinkage issue, but they redesigned the slide so that the unequal shrinkage of parts is no longer a problem.
The entry piece. “I redesigned the Chameleon from the original slide,” says Swaim. “I had to copy each piece, step by step, and improve on it. The straight, left, right, and exit pieces were basically sweeps. Those models were pretty easy. But the entry section was extremely complicated. I’ve been using Pro/ENGINEER since 1994, but I had never been trained in surfacing, and that piece has a lot of surfaces. So I had to look up how to do everything.”
With no training and little experience, it took Swaim about four or five days to deconstruct the original part, redesign it, and rebuild it, better and safer than before, using the surfacing capabilities in Pro/ENGINEER.
“Let’s say I change an angle and an affected surface can no longer be made in Pro/ENGINEER. The angle is supposed to meet up with the surface, but the surface is no longer there. The failure diagnostics window appears and lists the reason(s) for the failure. Usually, you are able to recreate the child feature very easily by redefining the feature, or picking new references, or whatever is necessary to resolve the failure.
Over the years I've worked in a lot of 3D programs and to me Pro/ENGINEER is the easiest. No matter what surface you want to create – or get rid of – you can always get to the end that you want.”
Scallops and pretties. Swaim also added a new hump to the top of the entry section – to discourage kids from climbing on top of it – and redesigned the scallop pattern on the bottom of the slide. “Each section of the old scallop pattern had a different width and height, making it look haphazard,” says Swaim.
“I sketched in several points and dimensioned them to all be the same distance from each other. Then I used these points to draw in the scallop pattern.” Now, every scallop is just like the next, and the scallops flow smoothly from section to section.
Those aesthetics are important says Geyer. “Customers who see a slide that’s all smooth surfaces are going to like that one a lot better than something with sharp edges. We’re trying to make it all look really nice, and Pro/ENGINEER surfacing capabilities helped make them look just how we wanted.”
In the end, says Swaim, the top section, and the rest of the slide, turned out great.
“At the National Recreation and Parks Association (NRPA) show in Reno last year, one of our competitors had a slide similar to the Chameleon, and they had to rasp the joints down to make them fit together really well.”
So the next time you’re pushing a little one down the slide, you’ll remember that Pro/ENGINEER may be behind the smooth ride.
Miracle Recreation Equipment Company, based out of Monett, Missouri, is one of the largest manufacturers of recreation equipment in the United States and design modular play systems, slides, swings, school sports equipment, outdoor fitness, park amenities and water and pool slides.
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