Whenplans for North America's largest five-axis gantry machine were set in motion,the challenge of establishing a massive machine with an X-axis three-quartersof a football field in length was daunting, to say the least. This massivemachine was developed by IngersollMachine Toolsfor use W Industries, a metalproducts manufacturer based in Detroit.

Since the spring of 2009, W Industries has been using theCybermill to machine huge, high-precision parts for aerospace and defenseapplications, with quotes now out on many alternative energy jobs. Using the giantCybermill, W Industries is currently working on a program for the AirBus A350for Spirit Airlines. This high-definition, high-tolerance project consists oftwo long tools for the fuselage, both 16 x 70 ft, which utilizes about 1/3 ofthe travel of the Cybermill.

Big,But Precise

Whendesigning a gantry machine that is 20 ft wide by 204 ft long (with 8 ft underits gantry), accurate, reliable linear scales at those long lengths are noteasily found. Heidenhain Corp. was approachedby Ingersoll to deliver these scales. The company delivered two, 72m linearscales, which Heidenhain claims are the world's largest, to run down the lengthof Cybermill's guideway, helping to enable around-the-clock operation.

To put the Cybermill's size into perspective, staff at WIndustries estimate that one could stack 78 Hummer H2 sport utility vehicles(without tires) two-high, three-wide, end-to-end within its table. Within thatamount of space, many kinds of large structures can be machined, includinglarge molds, jigs, fixtures and composite tooling. All three of theaxes on the mill include linear measurements provided by Heidenhain's LB 382Csealed linear scales (X axis is 200 ft, Y axis is 26 ft and Z axis is 8 ft).

LinearMeasurement

Long-length machining jobs are fast becoming a forté of WIndustries, enabled by the company's precision manufacturing capabilities. "Thepositional accuracy on these long Heidenhain linear scales is ±5 microns andthe repeatability is exceptional," says Martin Honer, a controls project engineer at Honer. "One of the reasons we chosethese scales were because of the LB scales' ability to carry distance-codedreference marks."

The distance-coded reference marks (semi-absolute) onthe LB scales allow it to ascertain its position at startup very quickly. Atevery startup, subsequent electronics find the absolute reference ("home"position) after traversing a very small distance. Conventional machinereferencing involves physically travelling the machine axes to a fixed homeposition that could potentially be many meters away. Distance-coded referencemarks speed and simplify such reference runs.

"On W Industries' Cybermill the X-axis homing cycle withdistance-coded reference marks can save more than three minutes compared to atypical system (with a home limit switch at one end of the travel and thegantry at the other end)," explains Honer.

Sincea combined total of more than 450 ft (150m) of these two LB distance-codedlinear scales had to be installed at W Industries, technicians from Heidenhainassisted in their installation. W Industries staff mounted the housings andeach 72m scale tape, bearing surface and protective sealing lips over afive-day period. The housings are dial-indicated and had to be within 0.004(four thousandths) flatness and parallel. In addition, the scanning head andbracket had to be mounted correctly providing for a 0.06 (60 thousandths) airgap over the entire 72m.

SpindleAccuracy

"Itis important to note that the tools on the spindle of the gantry are moving onsome pretty big arcs and they too need to be very accurate," says Honer.

TheCybermill's spindle head operates at 16,000 rpm with 50 kW of power. "Thisamounts to cutting very accurately at approximately 1,000 inches per minute,"explains Dave Hislop, W Industries' NC programming specialist.

Tohandle the measurement of the angles within the spindle, two absoluteHeidenhain RCN angle encoders are used: one on the C axis (the joint betweenthe RAM and the red spindle head) and on the B axis (the joint at the tool thatallows the tool to angle). The B axis must move ±100 degrees.

"Theangular positional accuracy on the spindle head is 20 arc seconds withrepeatability of 10 arc seconds," says Honer.

KathleenStoneski is the PR manager and technical writer for Heidenhain.