Stock Duplicating Using 3D Laser Scans
For more than a century, makers of rifle stocks have used large, complicated mechanical duplicators to reproduce stock designs. These contraptions rely on mechanical linkages to follow the lines of a stock and reproduce the shape on a new blank. Now new 3D scanning technology and CNC milling systems may render the mechanical stock duplicator obsolete. Laser Design Inc. (LDI) has developed a system of scanning lasers that creates an ultra-precise 3D model of a gunstock. Digital CAD data from the scans is then used to program a CNC milling machine that produces exact duplicates of the original stock.
Keystone Sporting Arms, LLC, of Milton, PA, has already started producing rifle stocks modeled on designs derived from laser scans. Keystone, one of the nation’s biggest producers of gunstocks, turned to the laser-scanning technology after Keystone purchased another stock-maker. Keystone wanted to continue to produce the acquired company’s legacy models. However, there were no CAD models for those older stock designs. Keystone had already invested heavily in the machining equipment and needed to be able to quickly generate CAD data from scanning a master model of the stock.
Keystone owner Steve McNeal knew that 3D laser scanning was able to produce excellent results when reverse-engineering rifle stocks. When an object is hard to measure manually or with a touch probe due to its irregular surface contours, non-contact 3D laser scanning can produce accurate CAD data very quickly. The Keystone stock scans were done with a 7-axis Faro Platinum articulating arm fitted with an SLP-330 laser probe. LSI’s technical experts helped Keystone create crisp well-defined edges and corners in the data files — this is key to the reverse-engineering process. The scanning process is fast, and exporting directly to MasterCAM for milling is extremely efficient.
Amazingly, the scans from a single stock contained over 18 million data coordinates. This enormous amount of data was then exported to MasterCAM to create the CNC toolpaths. From start to finish, the project took only three hours for the scanning, data editing, and export to MasterCAM.
How Laser Scanning Works
Scanning free-form shapes and irregular surfaces, such as curved gun stocks, is an ideal application for a non-contact laser scanner. Because the scanning system projects a line of laser light onto surfaces while cameras continuously triangulate the changing distance and profile of the laser line as it sweeps along, the problem of missing data on an irregularly-shaped surface is minimal. The operator moves the laser line back and forth over the area until the complete surface is captured. The capture progress is continuously monitored by the operator on the computer screen. The system measures details and complex geometry so that the object can be exactly replicated digitally. Laser scanners measure articles quickly, picking up to 75,000 coordinate points per second.
Scanning a gun stock offers certain special challenges. Most of the gun stock had a smoothly finished surface which produces excellent scan data with very precise tolerances. However, the front end of the stock, which had a rough wood grain, needed sanding to yield more usable 3D data. A feature that was somewhat challenging to scan was a 1.5″ hole in the stock. To capture the sides and bottom of the hole the scan technician positioned the laser directly over the top of the hole so the laser could “see” the bottom, then at a 45-degree angle for the sidewalls.