Software NAILS it

DN Staff

February 5, 2001

11 Min Read
Software NAILS it

One day in 1998, managers at ITW Paslode (Vernon Hills, IL) took a hard look at their flagship cordless power trim nailer, the IM250II. Without benefit of electricity or air pressure, that pressurized-gas-fueled tool uses an internal combustion piston to sink finishing nails.

Then they called their design team into a meeting and said, in effect-nice job, now improve it. To get you started, here are eleven design challenges for the handle alone:

Must mate with co-molded grip

Maintain part and assembly consistency

Blend ergonomically with a variety of users' hands

Avoid sharp edges and abrupt contours

Create a tough yet supple feel to grip

Avoid loose rattling fits

Withstand shock up to 800 g's

Protect against dirt, dust, and wood

Survive tool abuse at job site

Must be easily replaced

Must be easily molded and assembled

And if that's not tough enough, here are two more challenges from marketing: For aesthetic reasons, it can have no flat surfaces; and to compete in the marketplace, it has to be inexpensive.

With a workshop full of cutting edge software and engineering tools, the Paslode team was able to tackle this laundry list of improvements, using methods like rapid prototyping, laser networking, robotic fatigue testing, and collaborative CAD.

Armed with all that technology, Paslode released the IM250A cordless angled finish nailer in August 2000. Designed for carpenters who need to work in spaces too small to swing a hammer, its applications include door jambs, crown and baseboard molding, paneling, window casings, and cabinetry.

Here's how they did it.

Engineers used Unigraphics to model the new nail gun.

Computer systems.

The two Paslode buildings on its Vernon Hills campus are several blocks apart-close enough for engineers to walk between them at lunch time, but far enough that it would be cost-prohibitive to string computer cables between the buildings to ensure a connected network. So they stay connected with a line-of-sight laser network that blasts 100MB/sec. between the buildings, ensuring that every time someone makes a design change, it's instantly accessible by the rest of the team.

With a full team of engineers working on the project simultaneously, it's crucial to use a CAD system that can stand up to the collaboration. After testing seven other systems, the team chose Unigraphics.

"We use the Unigraphics Assembly module to do simultaneous design," says Patrick Driscoll, a senior project engineer.

Unigraphics' geometry linker allows designers to connect parts according to part files, not just default parametrics, so designers can choose to change only certain components, says Senior Design Engineer Walt Taylor. This allows the engineers to do non-parametric, freeform design-crucial in creating a nailer without flat surfaces.

The group runs Unigraphics 15 on Windows NT, with 22 users doing simultaneous modeling on different modules including assembly, machining, modeling, freeform, and rapid prototyping (RP) translator.

Paslode now does all but the most complex FEA in-house, using SRAC's COSMOS/DesignSTAR. And they use National Instruments' LabVIEW(TM)for data acquisition and control, data analysis, and data presentation.

Unigraphics' geometry linker lets engineers connect parts according to part files, no just default parameters.

Human-friendly design improvements.

Busy carpenters love lighter tools. So the IM250A is just 4.9 lbs., compared to its 5.5-lb. predecessor. The designers shaved weight by shrinking the tool's dimensions from 121/2x113/4 inches down to 111/2x103/4 inches, a task that demanded intensive solid modeling changes so they could still fit all the parts inside the smaller shell. They also specified a smaller gas cartridge-the new model has a fuel cell life of 1,200 nails, down from 2,400 nails.

Another way to make the gun easier to use was the soft, non-slip grip on the handle and the trigger. And engineers modified the safety guard so it has nailing guides that act as cross-hairs for accurate nailing.

Power Source. Like its predecessor, the IM250A is powered by a linear internal combustion motor, with its unique placement of a fan inside the combustion chamber. That fan and its 22 mm Maxon motor take so much punishment from the piston explosions that Paslode engineers had to design a rubber mounting to damp the g-forces.

With so much trouble to keep it alive, why is it important to include the fan? Once the fuel is manually injected, the fan helps to vaporize it, and to create a turbulent, hot-burning mix. After a spark lights the mixture, the combustion instantly reaches 2,000F, then the fan vents the fumes, cooling the cylinder in the process.

The sleeve bore is 1.5 inches, with a piston stroke of 3 inches, and a pre-ignition combustion chamber volume of 8 cubic inches. The shock of the piston is absorbed by a urethane bumper at the cylinder bottom.

After several hundred nail shots, the aluminum sleeve can reach 250-300F, and can start to misfire unless the carpenter gives the machine a short break. Cooling happens through exterior fins that act as heat sinks outside the cylinder, and by air flow created by the fan.

Tool maintenance has always included cleaning of combustion deposits caked onto the cylinder walls. So Paslode engineers changed the piston gasket so it created more friction, scraping the combustion deposits off the cylinder walls with each stroke, and tripling the interval between cleanings.

Materials. Having completed CAD models of the tool's insides and outsides, Paslode needed to start making physical parts.

They began with RP, creating overnight sample parts throughout the design cycle. A favorite machine was Stratasys' FDM(R)2000, which makes complex parts with the fused deposition modeling (FDM) method.

"We often make RP orders seven days a week," Driscoll says. "In fact, we use every type of rapid prototyping and rapid tooling we can get our hands on."

When it comes time to make production parts, Paslode, which is a division of industrial giant ITW (Illinois Tool Works Inc., Glenview, IL), contracts with local vendors to run injection molding machines for the nailer's plastic handle parts, and to run blow-molding machines for the nylon 6,6 tool cases.

That's especially important since each nail gun has about 180 parts, including 140 on the inside. So one of the main challenges is figuring out how to fit all those parts inside a sleek tool casing. With local plastic part production, engineers can quickly try different iterations.

"Open up the case, and it's like a car in there," Senior Design Engineer Scott Buetow says. "If one part changes, you've got to change how the assembly fits into the outside shell."

Quality assurance. Finally holding a working tool, the designers started many rounds of tough testing to trouble-shoot any problems.

Paslode standards call for nearly a quarter-million shots for fatigue testing. So Paslode uses round-the-clock robotic fatigue testing.

Another benefit of robotic testing is vibration analysis. With an internal combustion engine driving thousands of high-impact collisions, the interior parts tend to get rattled over time. One discovery was that a supplier had changed the grade of steel in a part, resulting in the gun popping open during firing. Another discovery was that the piston impact could jar the battery loose from its contacts. Both problems were easy to fix once Paslode had discovered them-they returned to higher-quality steel, and shrunk the battery compartment.

"It's the neatest product I've ever had the opportunity to work on," says Taylor. "It's just really cool."

Partners in Design

Go to www.designnews.com/info or enter

the number on the Reader Service Card:

1. Stratasys, Eden Prarie, MN. Product: FDM(R) 2000 machine, used for rapid prototyping. Enter 547

2. Unigraphics Solutions, St. Louis, MO. Product: Unigraphics 15 CAD software, used for solid modeling and design collaboration. Enter 548

3. Structural Research and Analysis Corp. (SRAC), Los Angeles, CA. Product: COSMOS/DesignSTAR, used for finite element analysis. Enter 549

4. National Instruments, Austin, TX. Product: LabVIEW(TM) software, used for data acquisition and analysis.

Enter 550

Timeline for design

1997 Paslode chooses Unigraphics for solid modeling software

Chooses COSMOS/DesignSTAR for FEA

Chooses LabVIEW for data acquisition

1998 The company releases the IM250II cordless power trim nailer, and asks engineers to start working on improvements for the next generation tool

1999 Paslode engineers make a first pass at the CAD model for the IM250A, and begin running stress analyses

Engineers start ordering rapid prototypes of parts iterations

With working prototypes of the new tool, engineers begin fatigue testing for quality assurance

2000 In August, Paslode releases the IM250A cordless angled

finish nailer

Professional carpenter gives nailgun a thumbs up

For a field test, Design News lent a nailer to professional carpenter Glen McLean, proprietor of the Brook and Bridle Inn, Wolfeboro, NH, and founder of Traditional Planning and Building, a contracting company in the same town.

"It's a beautifully crafted little product," McLean said. "A wonderfully weighted tool, its 4.9 pounds are easy on the arm, and it allows good visibility to the work surface, so you can see where you're putting that nail."

He does all the maintenance work for the central inn and its 11 surrounding cabins, including periodic repair, seasonal rehab on the cabins every year, and everything from framing doors to installing paneling and wainscoting.

"Besides the obvious benefit of not being tethered to an air compressor, it's well thought-out," he says. "It gives some portability to a maintenance department besides their cordless electric drill. Sometimes you just really want to put a nail in something, not a screw."

But he did have two complaints.

"It has a basic problem with the fuel delivery system," he says. "The literature doesn't give you a comfort level when you insert the cartridge that you've done it correctly."

The instructions take just a few words to describe installation of the fuel cell. The process begins when you snap the metering valve off the fuel cell and insert its stem into the nailer's orifice, then close the actuator cover, he says. But that little stem tab is not meant to be inside the orifice all the time-only for the instant that the nailer's guard has been depressed against a work surface, forcing the cell to release some fuel. So when he first inserted the fuel cell and found that the tab was not inside the orifice, he assumed something was wrong.

"It's funny that we'd be talking about such a well-engineered tool with a shortfall as basic as literature," he says.

McLean's second complaint was that the nailer "is biased toward the right-handed operator." The belt clip only works well if you're right-handed, and a left-handed user would have to switch hands in order to view the reload indicator.

"But I don't think you're talking about a big restraint," he says. "The battery charger worked great, and once the fuel cell was in there it worked great. The amount of thought that went into this is just tremendous."

Specs for Paslode Impulse IM250A

Weight:

Height:

Length:

Width:

Nail capacity:

Cycle rate, continuous:

Cycle rate, intermittent:

Fuel cell life:

Battery life:

Fastener lengths:

Shank diameter:

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