V-carving on a CNC: how it works and the settings that matter
A V-carve varies the tool's depth continuously so the sloping sides of a V-bit touch both walls of a shape. Narrow parts cut shallow, wide parts cut deep, and corners come out genuinely sharp because the tip of the V can reach into them. No round cutter can do that.
Why it exists
Take the letter A and try to cut it with a 1/8 inch end mill. Every inside corner comes out with a 1/16 inch radius, the point of the A is rounded off, and the thin parts of the strokes are wider than you drew them. It reads as a routed shape, not as lettering.
Now use a V-bit. Because the tool is a cone, the software can dip it deeper where the shape is wide and lift it where the shape is narrow, so the two sloping sides always touch the two walls. At a sharp corner, the tool rises until its point is at the corner itself. The result is crisp, and it is why V-carved signage looks the way it does.
Every point along the carve gets its own depth from the local width of the shape. You do not set the depth. The geometry sets it.
The settings
| Setting | What it does | When to change it |
|---|---|---|
| V-bit angle | Controls how deep any given width cuts | Narrower for fine detail, wider to stay shallow. See V-bits. |
| Start depth | Where the carve begins below zero | When carving into a pocket that has already been cleared |
| Flat depth | A maximum depth. Below it the bottom goes flat instead of continuing to a point. | When wide shapes would otherwise cut through the board |
| Clearance tool | A flat bit that removes the bulk of wide areas first | Any design with large open areas. Saves a lot of time and tool wear. |
| Ramp plunge | Enters each cut at an angle instead of driving the point straight down | Hard material, or a tip that is chipping on entry |
The names above are Vectric's, because that is what most hobby CNC users run. Other CAM calls the same things depth limit, maximum depth or cut depth. The behaviour is the same.
Flat depth, explained properly
Without a flat depth, a V-carve on a wide shape keeps going deeper until the two sides meet. On a wide letter stroke, a decorative border, or a filled background, that can be deeper than your material.
Flat depth says: go no deeper than this. Anything that would have gone deeper gets a flat bottom at that depth, with the V shape preserved at the edges where the shape is narrow enough. The visual result is a carved edge around a flat floor, which is usually what you wanted anyway.
Preparing the vectors
V-carving is far more sensitive to vector quality than any other toolpath, because it derives depth from the shape's local width. Bad vectors produce bad carves, and no setting fixes them:
- Vectors must be closed. An open shape has no inside, so there is no width to read.
- No overlapping or duplicate vectors. Two copies of the same letter on top of each other produce nonsense.
- No self-intersections. Script fonts where strokes cross themselves are a classic source of odd deep spots.
- Convert text to outlines before doing anything else, so the shapes are geometry rather than a font reference.
- Simplify traced artwork. A logo traced from a low resolution image has thousands of nodes and tiny wobbles, and the carve follows every one of them.
See vector troubleshooting for how to find and fix these.
Material choice matters more here
V-carving asks the material to hold a sharp edge at the top of the cut. Materials that do that well:
Settings for the carve itself
Starting point A V-carve is mostly a light cut, because the tool is only removing the small wedge the geometry calls for. Run a decent RPM, a moderate feed, and pay more attention to how sharp the bit is than to the numbers. The exceptions are large flat-depth areas, where the V-bit is working hard and a clearance tool should be doing that job instead.
What goes wrong
Almost every V-carving problem has a specific, identifiable cause. They are collected in V-carve troubleshooting: letters too deep, letters too shallow, rounded corners, missing detail, choppy text, uneven depth and visible flat bottoms.