Unlike a scale, a laser has no short-term errors that can stack up on long axes. The laser scale brings linear accuracy far below the repeatability of the ma-chine, about 1 part per million in 250 feet, despite mechanical shortcomings in the axis drives. This translates to about 0.0006 inch for a 600-inch axis. The longest axis under laser control at Alson is 1,000 inches. The only thing that changes is the reference point, where we feel the thermal compensation needs to emanate from, either from a hard stop or from the center of the part.
Some setups use a hard stop and the part grows from that point.
Other setups are designed to allow the part to grow equally from the center. The issue of growth is open for debate. You can chase 0.001 inch all over the place on a big part, but our methodology has worked. The system s processor manipulates data from temperature, pressure and humidity sensors to adjust the laser scale s signal for changes in the part. It also compensates for environmental changes that affect the refractive index of air, as well as the laser readouts.