Modelmakers Incorporated

Router Allows Prototype Maker to Increase Sales by 30%

The improved accuracy and faster turnaround made possible by a computer numeric controlled (CNC) router has helped generate a 30% increase in sales at Modelmakers Inc., a manufacturer of plastic prototypes, by increasing repeat business. Previously, prototypes were made by manually cutting parts out of plastic sheet stock and gluing them together. While this method resulted in a reasonable facsimile of a part, it was slow and lacked the high level of accuracy that some customers needed. With the CNC router, designs are carved out of plastic blocks, which are then used to produce silicone molds for urethane castings. Cast prototypes, generated directly from CAD data, are more accurate than the previous, pieced together models. "We have definitely seen an increase in business coming from customers who are very pleased with the accuracy in these prototypes and how quickly we can deliver them," says Buddy Akers, owner of Modelmakers Inc. He notes that the faster turnaround made possible by the CNC router is also improving profit margins at the company.

Modelmakers Inc., based in St. Louis, Missouri, is a service bureau supplying prototypes to companies that design and sell injection-molded parts. Before these companies order the very expensive steel molds used to mass produce their plastic products, they want to evaluate prototypes of new designs to make sure they are acceptable. This saves them the cost of modifying a mold, or building a new one, by letting them uncover problems with new products before they invest in the molds. Modelmakers Inc. has built prototypes for a wide range of plastic products, from toothbrushes to palettes used by the food service industry that are big enough for a person to stand up in.

Previous process
In the past, Modelmakers used conventional tools such as a manual router and table saw to make the prototypes. After receiving a CAD model of the part from the client, Akers would break it down into component parts such as ribs, top, bottom, and side panels and then cut these parts out of acrylonitrile butadiene styrene (ABS) plastic sheet stock by hand. The thickness of the sheet stock he used was as close as possible to the wall thickness of the part that was going to be injection molded. Once all the pieces were cut, they were glued together to represent the final product. This process took about five days. The resulting prototype was a close approximation of the final product. "We were always hoping for a better accuracy, but we were limited by the fact that we were working by hand," says Akers.

He decided to investigate CNC routers that could cut plastic directly from the client's CAD data. This would remove the accuracy restrictions imposed by human limitations. Even if the pieces were just cut by the computer controller router rather than by hand, the increase in accuracy would be significant. But Akers also wanted to try a new process for producing prototypes that would eliminate the need to assemble separate pieces. With a CNC router, he could program the router to cut away the shape of the CAD geometry from a block of butter board plastic. From that cavity he could then create a silicon mold. By filling the mold with urethane, he would then have a highly accurate wax model that "looks just like it came out of an injection molding machine," Akers says. "I felt that this approach would let us give companies the best window into how their products would actually appear once they were mass produced."

Akers was aware of two options in CNC equipment. The first

was heavy and expensive machining centers primarily designed for metalworking. They would deliver the accuracy he needed, but the smallest machining centers start at $30,000 and machines in this price range have working areas that are too small for all but a fraction of Akers' work. A machining center with a table large enough to handle nearly all his work would cost in the $100,000 price range, considerably more than he wanted to spend. His decision was also complicated by the fact that he does this work from the basement of his home. It would not be possible to get a larger machining center down the stairs. Akers rules out most routers, on the other hand, because they could not provide the accuracy he needs.

Then Akers heard about the Techno Series III PC-driven CNC router from Techno Inc., which provides the best of both worlds. Even though Akers bought the largest model available, the router could easily be installed in his basement. Also, for its price of $20,000 he got a 49" x 41" table with a 7" Z-axis stroke. Another benefit of the Techno router was that even though it was one of the more affordable CNC machines Akers looked at, it had a number of high-end features that would allow it to produce parts with the level of accuracy he wanted. Each Techno router is constructed from extruded aluminum profiles. It has four ground and hardened steel shafts and eight recirculating bearings in each axis. This shaft and bearing system produces very smooth, play-free motion and an extremely rigid system that produces high-quality cuts. Another feature of the machine that Akers found appealing was its use of anti-backlash ball screws, like those used in high-end machining centers. These screws have excellent power transmission due to the rolling ball contact between the nut and screws. This type of contact ensures low friction, low wear, and long life. The ball screws also make it possible to produce parts to the router resolution of 0.0005 inch.

Desktop manufacturing
The Techno router that Akers purchased was designed for production routing and drilling on a wide variety of materials including wood, plastic, MDF, solid surfacing materials, and nonferrous metals. The price included the Mastercam CNC programming system. Although that program was originally designed for metalworking, it is ideally suited for cutting plastic because of its ability to generate the most complex contours with little programming effort. Mastercam features true 3D geometry construction plus IGES, DXF, and CADL converters so that geometry can be uploaded from nearly any CAD system. "This system, which is what I call desktop manufacturing, put us in the ballgame for a minimal expense," says Akers. "Its affordable price gives the typical designer/machinist the ability to start his own company."

Since installing the Techno system, Akers produces most prototypes as cast wax models. He imports a CAD model, which is usually sent to him by email, into Mastercam. There he creates the toolpaths for the router. He secures the block of butter board onto the Techno machine and starts the cutting. First it roughs out the z dimension of the top of the part, and then it finishes the z cutting on that side. Akers flips the part and repeats the sequence on the bottom side. After a little manual clean up the part is filled with silicon to produce a silicon mold. That is filled with urethane to make a wax part. The entire process takes two days and is suitable for small- and medium-sized parts.

For larger parts, Akers uses the Techno router as a replacement for hand cutting plastic pieces. A good example is the prototype palettes he recently produced for a large bread maker. The palettes are used to stack and transport loaves of bread from the bakery, onto trucks, and into stores. To create this prototype, Akers used the CNC router to machine the bottom portion of the tray out of one piece of ABS plastic. He machined the sides out of another piece of plastic and then glued them together, producing a bread tray that looked just like the customer's drawing. Because he cut the pieces on the CNC router from the customer's CAD data, the prototype was highly accurate.

Akers also uses the router in his "labor of love" of building custom electric guitars. He believes the router is the key to producing a consistently excellent line of guitars that he plans eventually to sell in large quantities. Akers is in the process of setting up the Techno system to produce many of the components such as the tops, necks, and inlays that were formerly made by hand. "The Techno router will make this possible by giving me the ability to make a product that's repeatable every time," Akers says. "Also it will cut way down on the production time compared to carving pieces by hand. That's another big part of being able to offer these guitars on a regular basis."

For now, though, making prototypes is the main role for the Techno router. The 30% increase in sales that Modelmakers Inc. has experienced in less than a year of owning the machine means that it has more than paid for itself in that time. "With this router, we have been able to achieve the greater accuracy we wanted yet we also deliver parts quicker," Akers says. "It has been instrumental in improving our sales."