I treat the Sharpie's similar to a drag knife . Disable the spindle, set Z to top of material, define depth of cut for the pen at .05", and set profile or pocket toolpaths to .05". There's a 2.5D function in VCarve called fluting that will perform a ramped cut over the length of a profile, and it has options for:
- start depth and final depth of cut
- tool type
- to make the flute have a linear ramp, to ramp at start, to ramp at start and end (think bowl/concave shaped), to ramp for a fixed length
- to define the ramp as a linear motion or as a smooth motion (similar to cutting a pocket with a radius end mill VS flat end mill)
Because I was focused on just the flat drawing at the time, I hadn't thought about applying this to the Z axis (or even an A or B axis for rotary jobs), but it makes sense - merging the two scenarios that I originally wrote about as it boils down to modifying the feed rate (or spindle rate) based on possible parameters:
- distance to/from Z coordinate
- distance to/from X-Y coordinates
- distance to/from A-B coordinate (tricky if you allow your rotary to spin more than 360 degrees)
- spindle speed target = ST; spindle speed actual = SA; adjust feed rate by F%, adjust spindle rate by R%
As for implementing the gradient function or better yet, the radial modifier, I think that a simple linear percentage as you move between zones would give the best performance. I imagine that having more than one modifying layer could be tricky, do you default to the lowest value, the highest value, or a value between the two?
I know you can't or shouldn't make promises - this is only a suggestion based on an idea I had from a recent project. I can probably achieve a similar effect from having multiple overlapping toolpaths at different feed rates... I'll end up making a tool holder/mount that holds a modified fountain brush with an air line that keeps the reservoir pressurized. The trick will be to either hand edit the G-code to pulse a solenoid for semi-constant air pressure, or to find a way to have a post processor insert an M-code based on the distance traveled when the tool/brush is in use. Or just sit and watch it and make sure the ink doesn't run out or spit all over the project. It would probably be easier to just to paint the damn thing by hand... if I could paint.