What are the possible solutions for rotary engraving over curved or irregular surfaces?
I can think of a few ways to accomplish this. First would be to have the bit and collet in a splined holder that mates to a splined reciever chucked into the spindle. The splines would allow for bit rotation but also vertical travel up or down over gentle curves in the workpiece. The weight of the holder and/or springing in the reciever would mean that constant pressure was exerted regardless of the telescoping of the reciever.
The second and probably coolest would be for a microcontroller attached to a scanning touch or laser probe that rode next to and paralleled the engraving bit. This way if the probe could map the surface and send additional g-code interrupts to move Z up or down in real-time during the engraving if it encountered an elevation change.
Third would be for a very light handheld spindle to be attached to a suspension system with an adjustable spring or gas preload to effectively counteract almost all of the weight of the spindle, allowing the spindle to effectively "float" in Z. The workpiece itself would then act to drive the spindle up and down.
How is this problem actually solved in real life? I'm sure someone has thought of it, but I can't find ANYTHING really. Perhaps people just only bother to engrave on flat stuff?
Ideas please!