Shop Solutions: CAM Technology Repros Prop
In his quest to build a reproduction of one of the first planes that flew around the world, Bob Dempster, a relentless aeronautical researcher, was unable to find any plans or drawings of the original prop. This was a problem because a propeller had to be developed from scratch to match the power of the Liberty V-12 engine and flight characteristics of the vintage plane, which is a reproduction of the Seattle World Cruiser, one of the four original Air Service planes that had taken off from Seattle on its historic flight.
Only two of the original Douglas World Cruisers that started out from Seattle in 1924 actually made it around the world. Two others, the Seattle and the Boston, crashed, although the crews survived. Today the Chicago, completely restored, is on exhibit at the Smithsonian; and the New Orleans is in storage, awaiting preservation at the Los Angeles County Museum.
There was no way that Dempster’s team would be allowed to remove the propellers from these priceless historic artifacts so that they could be studied and recreated. And the project was too time-consuming and expensive for a commercial propeller manufacturer to take on, especially since Dempster only needed two props.
The solution came from chance encounters with other history buffs interested in preserving our aviation heritage and with CNC Software Inc. (Tolland, CT), developers of Mastercam.
While Dempster was on his search for the props, a team of volunteers in Seattle had nearly completed the reproduction of the plane, working in the same Boeing Seattle Plant II hangar where the historic Boeing B-17 and B-29 bombers were manufactured. In assembling it, they used the same meticulous nailing and gluing procedures that were used to manufacture the originals.
The plane’s Liberty V-12 engine was also nearing completion. It would need to be thoroughly checked out on a test stand. Before this could happen, however, Dempster would need to manufacture a test club, which is a sort of chopped off version of a propeller that serves as a counter-weight, allowing the massive 420-hp (313-kW) engine to be put through its paces. This need intensified the search for an appropriate propeller design.
The answer to Dempster’s problem came unexpectedly and almost by chance. One day, while wandering through the collection of the Seattle Museum of Flight, he came across a propeller that was tentatively identified as one from a Douglas World Cruiser. The curator allowed him to examine it more closely and, from its design features and markings, Dempster was able to verify the propeller’s authenticity. Now he knew there was an original propeller close at hand, but how could he capture data from it?
That answer came from another chance encounter. Steve Kidd, president of Cimtech, a Seattle-based Mastercam dealer and provider of computer integrated manufacturing services, was volunteering his services in the same Boeing hangar, working on the B-17 and B-29 bomber restoration projects. He and Dempster got involved in a lively conversation one day about each other’s project. When Kidd heard about the difficulties Dempster was having obtaining a propeller design and club for engine testing, he volunteered to reverse-engineer one for him.
Messrs. Dempster and Kidd approached Seattle’s Museum of Flight, which graciously allowed them to remove the propeller from its collection for a day so this could be done. Using a hand-held laser scanner made by Creaform (Levis, Quebec, Canada) and high-end software by Rapidform Inc. (Sunnyvale, CA), David Arena of Cimtech was able to accurately capture all of the geometric data from the huge 10' 4.5" (3.2-m) prop in less than a day. Data were exported as an STL file, which can be read natively in Mastercam X5 Mill software from Mastercam/CNC Software Inc. (Tolland, CT). Nothing else had to be done to the data in preparation for creating CNC manufacturing toolpaths in the CAM software. Rich Greer of Cimtech then programmed the project making a file over 250 MByte ready for the mill to do its work.
Back at Steve Kidd’s shop, the club would be machined from a huge block of birch weighing 300 lb (136 kg) and measuring 96" (2.4-m) long. The real challenge was cutting the 7.5' (2.3-m) club using a VF4 milling machine from Haas Automation Inc. (Oxnard, CA) with only 50" (1.27 m) of travel.
"We used a technique called picture-frame machining that is used widely in aerospace applications for making large, monolithic machine projects, where both sides of the material need to be accurately machined. In this instance, the technique involves machining a blank with straight parallel and a bore to pick up center. These characteristics allowed us to accurately pick up the location of the blank for each stage of the machining process," Kidd explains.
"First we roughed and machined one side of the prop in three sections along the X travel. We supported the part with outriggers when it overlapped either side of the table. Then we flipped the part and did three more picture-frame machining sequences on the other side."
The end result of this process was a perfect part held within a frame of birch material by several small tabs that were cut using a Sawzall and finished by hand. The flat parallel frame and bore allowed the part to be accurately located after each move, so that machining could be held to within 0.001" (0.03 mm).
The finished propeller was reduced to 59 lb (27 kg) with some hand sanding, and then the project was delivered to the Seattle Cruiser. Ideally, this process would have been completed after six setups. However, circumstances intervened that made it necessary to interrupt the machining process over and over again.
In addition to contributing services to the flight museums and historic aviation causes, Cimtech also provides manufacturing services for a medical device to several specialized burn-center hospitals around the country. Kidd and his staff have developed a facial burn mask with the burn team at Harbor View Hospital in Seattle.
When Bob Dempster’s engine club was being manufactured, Cimtech had to break down the setup approximately eight times so that burn masks could be rushed through. Instead of being a six-setup process, picture-frame machining of the test club required about 14 setups. Even so, the fidelity of this sculptured part to the CAD model was exceptionally high.
As this article went to press, the rebuilt engine was being tested using the test club. Cimtech sent the Mastercam file to the Sensenich Wood Propeller Co. (Plant City, FL) where it will be used to manufacture the 10' 4.5" (3.2-m) propeller. Dempster says the Seattle World Cruiser prop is much larger than any in use today. So it may be necessary for Sensenich to be creative in manufacturing the huge historic prop on its conventional-size equipment.
During the summer of 2011, Dempster expects all the pieces of his plane to come together, and he will put the Seattle World Cruiser through more than 40 hr of in-flight tests in order for it to meet FAA certification requirements. Then, look out world—here they come! They being Dempster and his co-pilots including his wife Diane (a licensed pilot herself and a faculty member of Embry-Riddle Aeronautical University), and a host of aerospace VIP co-pilots who will join Dempster on various legs of the journey.
Dempster says he is no risk-taker. Although the Seattle Cruiser is the same shape, size, and weight as the original, it will rely on numerous material innovations and electronic technologies to make the plane more durable and navigation much more dependable.
The flight in the open-cockpit plane will come off pretty much the way it was done for two of the planes that completed the journey in 1924. Half of the landings will be done on pontoons and half on wheels. The Seattle World Cruiser will travel 23,942 nautical miles in four to eight-hr hops over a period of about 175 days. Dempster is confident that, unlike the original, his World Cruiser will ultimately return to Seattle, where it will move to Seattle’s Museum of Flight to be admired for generations by lovers of aviation history.
"The Mastercam program and all of the services provided to us by Steve Kidd of Cimtech have been invaluable to us, not only for obtaining our propeller but for many other projects associated with the Seattle World Cruiser," says Dempster. "Mastercam allowed us to quickly create CNC toolpaths from an STL file generated from scanned-in data. Then, it gave us the ability to make an oversized test club on a standard mill using the picture-frame machining technique. Finally, we were able to e-mail the Mastercam file to the propeller manufacturer to make our 10' 4.5" [3.2-m] prop using similar techniques. All of this help made it possible to recreate a propeller design that had nearly disappeared from the planet." ME
For more information from Mastercam/CNC Software Inc., go to www.mastercam.com, or phone: 860-875-5006; from Rapidform Inc. go to www.rapidform.com, or phone 408-856-6200; from Creaform, go to www.creaform3d.com, or phone 418-833-4446.
Game Changer for Finishing
Surfaces of Ammo Dies
The use of manual processes for surface-finishing operations can be far more costly than properly automating the processes with the right tools. Repetitive-motion tasks and other ergonomic deficiencies not only result in discomfort and injuries, but also in operator fatigue that shrinks productivity and compromises product quality.
In the case of RCBS (Oroville, CA), a member of ATK’s Security and Sporting Group (Anoka, MN) and a leading producer of high-quality ammunition-reloading equipment, concerns about the negative aspects of its manual surface-finishing operation led to a company goal to eliminate the risk of injuries and operator-fatigue problems.
ATK Security and Sporting is a leading technology developer and supplier of ammunition for law enforcement, military, and sporting applications; a manufacturer of optics, reloading gear, and sport-shooting accessories; and a leading producer of tactical accessories. The company serves sport-shooting enthusiasts, law-enforcement professionals, military, and tactical markets worldwide. In addition to RCBS, the group’s products include some of the most widely known and respected brands in the industry, including Federal Premium, CCI, Speer, Alliant Powder, Champion, Weaver, Eagle Industries, and Blackhawk! Industries.
Among its product offerings, RCBS offers a variety of steel reloading dies for rifles and pistols. These dies are typically sold in sets for each caliber to be reloaded.
"We produce hundreds of thousands of these dies every year," says Tim Taylor, an RCBS engineer. "So the achievement of consistent, high-quality surface finish, as well as avoidance of worker discomfort, became a high priority that got a lot of attention."
One of RCBS’s production processes involved hand-finishing steel ammunition-reloading die bores. Workers would wrap emery cloth on rods and polish the internal surface of the dies, which required extensive manual labor on every die.
"The problems with this laborious process included some inconsistencies in the surface finishes," explains Taylor. "This resulted from ergonomic factors, which were a big consideration. Because this was a repetitive-motion job, some workers experienced discomfort or problems with wrists, shoulders, and backs."
According to Taylor, these issues led RCBS to explore process improvements, including CNC equipment and tools. At a trade show, Taylor discovered what looked like a possible solution to his surface finishing and ergonomic requirements, a flexible ball-style honing brush made by Brush Research Manufacturing Co. (BRM; Los Angeles) that could be tailored to meet the die bore finishing requirement, and could also be attached to RCBS’s recently acquired CNC equipment.
The BRM tool, known as the Flex-Hone, is used widely throughout industry for deburring, plateau honing, and deglazing, edge blending, and polishing. Available in many sizes and finishing materials, the Flex-Hone is composed of a shaft from which extended nylon filaments mounted with hundreds of abrasive grit globules.
The company’s Flex-Hone for Firearms line already enjoyed a positive reputation within the industry for extending the life of firearms. Beyond producing a beautiful finish, the hone removes the microscopic "peaks" and "valleys" that can affect the performance and life of the firearm.
In use, the Flex-Hone’s flexible construction makes the tool both self-centering and self-adjusting to compensate for any wear. In accordance with the abrasive type and grit size, precise surface finishes ranging from mirror finishes to cross-hatching are automatically accomplished.
"After we decided to test the Flex-Hone, BRM gave us some recommendations and basic guidelines," says Taylor. "I had a spare CNC mill, so I made up a fixture and started trying the process at different speeds and feeds. It took several process changes before we were able to consistently meet our surface finish requirements."
BRM developed a series of fine grit models for die applications where RCBS used progressively finer grits to achieve their results. "Depending on the die, we use multiple hone sizes as well as varying grit materials and number of strokes," Taylor says.
Taylor says that the surface finish of the RCBS steel dies is submicron (roughness value) when they come off the machine. After the Flex-Hone finishing operation, the surface finish is improved by a factor of eight.
With the steel-die finishing solution a success, RCBS decided to try the flexible hone solution on its dies that feature a much harder carbide material.
"On those we use a Flex-Hone brush with diamond crystal grit, and basically achieve the same type of results in terms of automation and finish," Taylor says. "The finish looks like a mirror when we’re done."
Initially, Taylor wrote a basic honing program for the CNC mill. Once he decided to go online with the process, he wrote a parametric program to automate the process. Essentially, the CNC operator inputs four or five different parameters, e.g. bore length and ID. The CNC performs the necessary calculations, and then selects the corresponding Flex-Hone brush. Based on the input, the CNC also calculates the number of tool strokes, rpm, and so on.
"The new automated process is a real game changer," Taylor says. "It is probably 60–70% more efficient than doing it by hand. Also, there was a substantial increase in quality. It’s better and faster. But the ergonomic improvement—removal of the potential for operator discomfort and injury—alone would have been enough to justify the new process. For instance, there are no more repetitive motion injuries, because there is no more repetitive motion in the polishing. So, that is a 100% improvement."ME
For more information about Brush Research Mfg. Co. Inc. go to
www.brushresearch.com, or phone 323-261-2193.
Software Reinvents the Exercise Wheel
Leading composite specialist, Lamiflex, has used the VISI suite of design and manufacturing tools from Vero Software UK Ltd. (Gloucestershire, England) to put a modern spin on the traditional exercise bike, creating an innovative piece of luxury fitness equipment.
The Lamiflex Group (Bergamo, Italy) has been involved with composite materials for over 30 years, supporting various industries such as the aerospace, medical, telecommunications, and the sports sector.
The company started production in 1976, and invented and developed ribbon products made from composite materials for the textile-machinery sector. However, continuing research and investment have allowed Lamiflex to expand into other market sectors, such as aerospace, where they use a special autoclave polymerization of composite materials process, certified by AgustaWestland (Farnborough, England), which produces both stiff and flexible lightweight ducts for environmental control systems installed in aircraft or high-performance vehicles and machinery used by the military.
Composite materials are, by definition, structures made up of several component materials, typically thermoset resins strengthened with carbon, Kevlar, or glass fibers that provide certain characteristics (usually mechanical), and a matrix that holds the fibers in position, protects them, and offers other specific characteristics for particular applications. The main purpose behind the development of composite materials is, without a doubt, their high mechanical strength, letting one get performance levels similar to those of metal (or higher), but at lighter weight (50% less).
In 2009, Lamiflex Group helped develop a piece of fitness equipment designed by Italian product designer Luca Schieppati. The Ciclotte is an exercise bike with an ultramodern carbon-fiber frame, touch-screen display, and reduced pedal distance to ensure correct biomechanics throughout the leg's rotational movement.
The large central wheel forms the cornerstone of the design and is reminiscent of the classic unicycles dating back to the end of the 1800s. The Ciclotte has been designed to accurately reproduce the dynamics and performance of on-road pedalling, and is ideal for high-intensity aerobic training such as "spinning," which is all possible because of the epicycloid crank system. A dual satellite system uses four gears with varying cogs in a 58-mm functional space. Multiplying the number of flywheel rotations, about four flywheel rotations to every pedal rotation, helps generate a high-intensity magnetic field (from the main wheel), which maximizes the resistance level and produces plenty of thigh-burning resistance.
The Ciclotte is a follow on from the Ciclò project, a prototype of a single-wheel city bike, which is now part of the permanent collection exhibited at the Triennale Design Museum in Milan.
At the beginning of 2009, a first aesthetic prototype was produced to test the market feedback before moving onto a fully functional prototype. To guarantee the exact requirements and size of all functional mechanical components, including the carbon-fiber handlebar and saddle, all components were designed in 3-D and simulated as a virtual assembly to highlight any potential issues prior to the assembling procedure, where over 60 separate components are finally brought together.
To coincide with the Ciclotte project, Lamiflex also took time to evaluate the software market and invest in a new integrated CAD/CAM system. "Previously at Lamiflex, we used a parametric CAD system that we found difficult to use and quite restrictive when working with complex surface forms. After extensive benchmark testing, we decided to implement VISI from Vero Software, as we believed it offered the best balance between performance and price. We are currently running multiple licenses of VISI Modelling and VISI Analysis for Design, and VISI Machining with Compass Technology for 2-D through to five-axis milling," explains CAD designer, Marco Perani.
"We have used VISI for the design and manufacture of all composite mold parts used to build the Ciclotte. With regards to the molds for the carbon-fiber wheel and the handlebar, all of this was achieved in less than 100 hr of CAD work," says Federico Carrara, R&D director and Ciclotte project leader.
Once the molds were complete (and polished), the fabric and epoxy resin were applied. Molds, fabric, and resin were then inserted into a vacuum bag, and placed inside the autoclave for the curing process. Once hardened, the parts are then passed through to the CAM department for finish machining.
"At Lamiflex, we run several milling machines including two simultaneous five-axis CNCs running VISI Machining. For the finish machining of the composite products, the ‘trimming’ method is often used, where the side of the tool is driven along the surface edge. For additional control, synchronization curves can be used to control the tool movement in local areas where the potential direction changes are at their most extreme. For the machining of planar holes, the tool is tilted perpendicular to the surface, but when product holes are difficult to reach, an extra tilting of the tool is required in order to avoid collision with the toolholder. When the toolpath is complete, the machine operator is able to virtually walk through the complete program using the kinematic simulator, and prove the toolpath is collision-free," Carrara explains.
He concludes, "Introducing the software has streamlined our manufacturing processes, reduced the potential for error, and ultimately increased our productivity."ME
For more information from Vero USA Inc., go to
www.veroint.com, or phone 248-869-4040.
This article was first published in the April 2011 edition of Manufacturing Engineering magazine. Click here for PDF.