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V-Carve Inlay on Curved Model

Posted: Wed Dec 19, 2018 7:29 am
by unicacher
I've been using v-carve inlays with much success and decided to try to up my game by projecting a v-carve inlay onto a curved surface. My first attempt was a partial success. Using an ellipse, I created a shape with about a 20 degree angled profile, and projected text onto it. No big deal so far.

For the plug, I copied the shape to the back side and switched it to subtract mode. The reverse text with a bounding box was projected onto that surface with a v-carve toolpath with 0.1 start depth and 0.2 flat depth. (That's the simple version. There were a few other pieces added to simplify machining.)

End result, a piece that fit beautifully... in the middle. The outer border I created didn't mate at all.

Why, I wondered? My theory is that the farther the path strayed from the top surface, the more distortion would result, but analysis of the toolpath makes it a bit more complicated. I'm hoping somebody with a sharper mind than mind can find my flaws.

The magic checkbox to make this happen:
Project Onto.JPG
Preview of the V-carve:
Negative Top.jpg
Showing the curved projection!
Negative Iso.jpg
Copy the shape and select subtract from model:
Back Side Subtract Model.JPG
Settings for the plug, including project to model. For this to work, the model on the front side has to be deselected.
Back Side V-Carve.JPG
Here's where it gets wonky. When using start depth on flat surfaces, vertical walls are created as the tool plunges the extra 0.1", which isn't a big deal for the inlays because the wall is above the inlay part. However, in this application the extra vertical travel doesn't translate with the curvature. The two highlighted areas show where the rectangle doesn't have straight edges, because the sides are influenced by the nearby vectors. Also, the ring border isn't consistent.
Negative Iso Annotated.jpg
Can anybody think of a solution to this? Offset vectors instead of start depth? Move the model plane 0.1" instead of using a start depth? If our collective minds could solve this, it will elevate the CNC game!

Re: V-Carve Inlay on Curved Model

Posted: Wed Dec 19, 2018 7:31 am
by unicacher
Here's the test file if you want to play with it.