Machine Design For Complex Carving

      It's hard to do, and might not pay off. April 10, 2005

I am in the process of building a CNC router to machine solid hard wood and would like to know the following:

1. The machine will be mainly doing 3D carving. What speed of traverse on the axis will be required X, Y, Z - this will influence the design of the machine i.e. rotating ball screw or rotating shafts (speed limits to prevent whip - I intend to use TC tooling wherever possible).

2. What advantage, if any, will a 5 axis machine have over the 3 axis (imagine fancy nurbs and curves in the solid wood end product) as I was thinking a 3 axis machine can have a long 30 inch Z travel. Any comments would be appreciated.

Forum Responses
(CNC Forum)
From contributor A:
Most people do not carve wood with a machine because of the time involved. It is usually much cheaper to have someone carve the items by hand. Companies like Disney will scan a model into point clouds and then use a program, such as Paraform, create NURB surfaces from the point clouds generated from the scanner. They will then scale the item, if necessary, and then glue up 4" thick blocks of foam and cut the foam on the machine.

You may want to cut something soft like this and then create a casting if you have multiple items. Sorry, I do not know the speeds you asked for, but I am sure someone else will. You may also want to consider having the machine start the carving and then have a carver finish it up.

From contributor B:
Many long years ago, I supervised machine carving departments for a couple of high end furniture manufacturers. The multiple spindle (12 to 40 spindles) carving machines used a pattern that the operator would trace with a stylus. All of the spindles were mounted on floating beam in line with the stylus, and carried tools that matched the stylus size and shape. The stylus and spindles had three axes of motion. The pattern and stock could be mounted flat, or between rotating centers depending on job requirements. Results varied wildly with operator skill, but the best carvers could do an excellent job with these three axis machines. Motion was quite slow (usually less than 100 IPM) because of the weak (human) drive system.

The next generation of carving technology used the same basic machine, but with a robotic arm taking the place of the carver. A skilled carver would cut a single copy while the arm recorded all movement. When the program was run, the feed rate was typically speeded up beyond human capabilities. Still, these machines were not very rigid, and the cutting speeds were still typically under 200 IPM or so.

After the robot arm retrofit machines came the purpose built four and five axis multiple spindle carvers from Kitako, and CMS. These machines came with a programming station that the operator would use to record programming motion just as with the robot arm. Cutting speeds of 600 IPM were possible, with positioning speeds in the 1500 IPM range. Since carving is slow and carved parts tend to be small, this was more than adequate.

Five axis single spindle CNC routers came on line about the same time as the CNC carving machines. I had the pleasure to work with the first Zuckermann Zuma imported into this country. These did not carve so much as they profiled in five axes. Programming was sometimes from a geometry file and sometimes by teach-in method. You could actually carve on these machines, but the programming was difficult, the output was low, and the quality was not typically very good. You may have seen these machines carving at trade shows, but there was very little being done on a commercial basis.

I recommend you find someone with a CNC carving machine and take a look. There are not too many out there, but I'm sure it would be worth a trip.

From contributor C:
TC as in Tugsten Carbide. With no helical angle on the TC tools you will be sanding many of your parts. I suggest using Solid Carbide tooling, as finishes will be much better with little or no sanding. Our ball end ruffers are being used by a number of firms that have single or multiple heads. This allows for hogging most of the material and provides a smooth finish. On a 5 axis you will also require much longer tools for the depth of cut. Our standard tools for this start at 5" and up to 12". Your RPMs will be 9-10000 on larger diameter tools and 15K on smaller tools. 1-200 IPM feed speeds, again depending on part and the detail of the project.

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