Wood carving with a CNC router.
The first successful attempt in automating this operation was developed by Thermwood Corporation in 1989. It consisted of a gantry which was placed over and connected to a multi-spindle carving machine. As the skilled operator carved a part, the computer control recorded every motion. When the part was completed, the motions were replayed. Future production of that part was then automatic.
This system requires fewer skilled operators, however, the production rate for each machine is unchanged since the machine uses a recording of an operator's movements. Speed is limited by the low horsepower, slow RPM carving spindles and also by the amount of force the human operator could generate during programming. It is still necessary to have a skilled carving operator, at least to generate the initial programs.
It is apparent that if a CNC router could be made to carve, higher production rates would result since the higher horsepower heads and powerful machine drives could remove material faster.
The first automated carvers required Thermwood to develop an advanced CNC control which evolved into the 91000 SuperControl. However, carving with a CNC router had to wait for even more powerful computers.
At the 1995 Anaheim Woodworking Show, Thermwood announced that these more powerful controls were now standard on all Thermwood routers and that new Thermwood routers were capable of three-dimensional wood carving. The company also announced a series of options which configure a Thermwood router for volume production carving.
The most unique part of this announcement, however, is a new programming system which can be operated by almost anyone.
Parts carved on a CNC router generally go through three steps. The first is shaping and smoothing. A ball nosed router bit traces the part creating a smooth, but rounded shape. A square bottom tool is used to cut the square inside corners and a pointed detail bit cuts the lines in fine detail. The result is a high-quality, carved part produced much faster than even an automated multi-spindle carving machine.
Programming the shaping and smoothing pass has been automated. Using a simple procedure, the machine automatically scans back and forth over the leg, indexing each pass until the smoothing program is complete. The process can take anywhere from an hour to 12 hours or more. However, scanning can be set up and run at night, without an attendant, leaving the machine available for production during the day.
What's a drag?
Squaring and detailing are programmed using a "drag" programming mode. The operator guides a probe around the model creating the program. The machine is powered during this process so it requires little physical force or skill to execute. The programming speed has no effect on execution speed of the program. Paths can be generated slowly and carefully. Programming is used strictly to define the path. Execution speed is determined by the machine and will be many times faster than program speed.
The largest potential impact of this new technology is that it opens up three-dimensional wood carving to companies who do not employ skilled woodcarvers today. Any three-dimensional part can now be easily programmed and carved by almost anyone.
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|Title Annotation:||computer numerical control|
|Publication:||Wood & Wood Products|
|Date:||Dec 1, 1995|
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