Routers ride the rail to success

ControlDesign.com

Keywords: CNC, computer numeric control, router, linear ball screw, router machine, woodworking and C.R. Onsrud

This article takes a look at how the linear ball screw choices made by a North Carolina-based CNC router OEM resulted in a simpler, more productive router machine for applications in the woodworking industry.

By Tom Onsrud, President, C.R. Onsrud Inc.

AS IN ALL high-quality machining applications, customers’ expectations of new-generation machines converge around the familiar “bigger, faster, better” mantra. This certainly is true in the woodworking industry, where manufacturers look for larger work areas to do bigger jobs with more speed and accuracy.

View Video Clips of Onsrud routers in action

C.R. Onsrud’s employees pride themselves on a pretty clear objective: to design and build the world’s best CNC routers. For four generations, this family-owned business in Troutman, N.C., has aimed to set the standard in the woodworking industry for advanced routers with faster machining, higher productivity, and greater flexibility. Wood panels such as doors, frames, and complex multi-level routings, and 3-D objects such as volutes and gun stocks, are some of the products cut by Onsrud’s routers. Aluminum, steel, plastics, and thermoplastics also are part of the production mix.

For C.R. Onsrud’s machine designers, a good router recipe comes from using exceptional ingredients. “We try to make the best-designed, best-built, best-supported machines on the market,” says John Onsrud, executive vice president, and one of three brothers running the company. “We make a premium piece of equipment with top-shelf components. We reveal the names of our component suppliers in our marketing literature because we’re proud of what we put in our machines.”

Under the Hood
A closer look at Onsrud’s CNC routers reveals that speed, rigidity, dependability, and quality are the primary objectives of the entire router design. Built to be some of the heaviest, fastest, highest-performing machines on the market, Onsrud’s HD Series Super Heavy Duty and Extreme Duty five-axis machines are the flagships of the company’s CNC router line (See Figure 1 below). These five-axis machines use cast iron for all major components that support the cutting spindle. Cast iron provides up to 10 times the damping capacity of steel, and the castings are internally reinforced with heavy ribs to resist flex and damp vibrations.

	FIGURE 1: FLAT MEANS FAST
	The ball rail selection for these new routers provides a clear benefit in machine assembly time. Previous solutions required shimming the table to achieve the required perfectly flat work table plane—a process that could take eight hours per machine.

The Extreme Duty fixed-bridge twin table, for example, can machine at speeds to 4,750 in/min using a ball screw on the Y-axis. This router is characterized by two tables, which come in sizes from 5x6 ft up to 5x16 ft, to produce wood panels up to 24 ft in length, depending on machine model.

The linear guides responsible for the X-axis motion of these work tables feature a runner-block design that helps Onsrud shorten assembly time, cut machine cycle times, increase production, and reduce lubrication and maintenance costs. For example, the runner block enables travel speeds up to 5 m/sec. with excellent dynamic load capacity, which is attributed to minimal friction during ball recirculation and optimized force distribution within the runner block. The lubrication system uses a foam insert to release lubrication to the balls over time and provides 10 million meters of maintenance-free travel and substantial reductions in lubrication-related maintenance costs.

This World is Flat
Among the various reasons that drove C.R. Onsrud engineers to choose Rexroth’s Ball Rails and ball screws over others they researched, there were two that stood out. “First, the availability and quick delivery of the Ball Rails and ball screws in 6 m lengths is almost unheard of, since most suppliers stock only 4 m lengths, and require long lead times for anything longer,” says Onsrud. “As woodworking customers require larger work areas, the machines they use also get larger. Getting rails in longer lengths allows us to avoid having to use two rails joined by a butt joint. It’s hard to talk to a customer about a butt-joint rail, so the single piece is important.”

Second, these ball rails also give Onsrud’s company a clear benefit in machine assembly. Though the work table must be perfectly flat, he says, a small bit of unevenness will exist no matter how carefully the table is made. Previously, when Onsrud tried other linear solutions, the standard procedure was to shim the table to achieve the required flatness—a process that could take up to eight hours per machine.

“Shimming was required not only to ensure a flat surface, but also to allow the rails to run smoothly,” says Onsrud. “If the rail flexes to the table, stress is added, so the table doesn’t run smoothly.” When a heavier load resulting from increased friction between rail and runner block puts added stresses the servo motors, the result usually is greater wear and tear on components and reduced reliability.