I can/do. (to some extent)
Here's the deal on this as there are a couple ways to skin this cat.
One is with a probe. The other is with a solid model.
We'll cover the probe first as it is pretty much the only one being used in the industry today.
A Reneshaw probe is nothing more than a lollypop that sticks out of a tool holder that records a position when it bumps into something. A program is written so that it works within a confined box. The machine moves the probe until it contacts something (in this case our master blank stock) and that point is recorded in space. When your all done you have a cloud of 3 dimensional positions recorded in space. This "point cloud" then has line geometry assigned to it and toolpaths are then generated from the lines.
Advantages: Relatively simple/fast to replicate/duplicate a pre-existing design.
Disadvantages: I'll cover these individually.
1. It's almost impossible to manipulate a point cloud. This means what you copy is what you get. Since it's lines and dots there's no real way to tie it all together and be able to stretch or twist while having the rest of it still flow together. This creates its own set of challenges when it comes to machining it. The short line segments aren't tied together very elegantly and this can cause erratic/spastic feeding which reduces surface finish quality and is hard on the machine. There are some filtering options but they are a band aid fix to a bigger issue.
2. Tool selection is limited to the diameter of the probe that generated the point cloud. You can't (well you can, but it'll look like crap) probe with a 1/4 stylus and then machine with a 3/8 ball. The offset will be wrong and there's no real way to 'fix' that using this method.
3. Machining options are limited. A probe does its best to work at a right angle to a stock and along the Z axis of the machine. A tool will also machine this way. With a ball endmill on wood you end up with a point line of crush at the tip of the tool. This is because no matter how fast you spin that tool, the center is basically motionless. This chews through the wood and compresses the fibers as a consequence. When you add finish the grain raises and you have an extra step now to sand out the raised grain. Not a show stopper but a pain in the arse.
Alternatives:
Free form surfacing and solid models.
The software for doing this exists and its now available. It's primary use is in aerospace and mold making. Drawing a stock though isn't as easy as it initially appears and there in lies the challenge. Three of us have been fiddling with this since 2004 and we just NOW (a week ago) stumbled onto a procedure that shows some promise.
The advantages are numerous. The outside geometry can be manipulated to fit an individual. The tooling options are much greater. The machining options in terms of using canted multi axis processes are almost endless, and the cycle times are greatly reduced since more effective tools can be used to get the job done.
Disadvantages:
Expensive/time consuming to develop and bring to fruition.
Hope this helped answer your question.
C
