V-bits and engraving bits for CNC
A V-bit cuts a V-shaped groove that gets deeper as the shape gets wider. A wide angle like 90 degrees stays shallow and suits small text and thin material. A narrow angle like 30 degrees gets deep fast but reaches into fine detail. 60 degrees is the usual general purpose choice.
How a V-bit is different
Every other bit cuts a constant width regardless of depth. A V-bit does not: it is a cone, so the deeper it goes, the wider the cut. That single property is what makes V-carving work, because software can vary the depth so the two sloping sides touch both walls of a shape exactly.
Angle is the full included angle, which is how V-bits are sold. A 90 degree bit cuts to half the width. A 60 degree bit cuts to about 0.87 times the width. A 30 degree bit cuts to about 1.87 times the width.
Choosing an angle
| Angle | Depth at 1/4 inch wide | Best for | Watch out for |
|---|---|---|---|
| 20 to 30 degrees | About 0.47 to 0.71 in | Very fine detail, small text, intricate line art | Cuts extremely deep on anything wide. Fragile tip. |
| 45 degrees | About 0.30 in | Detailed lettering, medium signs | Still deep on wide strokes |
| 60 degrees | About 0.22 in | General purpose signage. The most useful single V-bit. | Loses some very fine detail compared to 30 |
| 90 degrees | 0.125 in | Thin material, large text, shallow decorative carving | Fine detail disappears; wide strokes look shallow |
| 120 degrees and wider | About 0.07 in | Very shallow decorative lines, chamfering | Almost no depth variation to read as carving |
Formula Those depths come straight from the formula above, not from a chart. Change the width and they all scale with it.
The tradeoff, stated plainly
Narrow angles reach into detail that wide angles cannot, because the tip is a finer point. Wide angles keep the carve shallow so it fits in your material. You cannot have both, and this is the source of most V-carving frustration:
- Fine details vanishing? The angle is too wide for that detail. Go narrower.
- Letters cutting right through the board? The angle is too narrow for those stroke widths. Go wider, or set a flat depth limit.
Flat tip V-bits
Some V-bits have a small flat at the point instead of a perfect sharp tip, described as something like a 60 degree bit with a 0.032 inch flat. Two consequences:
- They are more durable. A true point is fragile and dulls quickly, and once the tip is dull the fine detail it existed for is gone.
- They have a minimum cut width. The flat cannot cut anything narrower than itself, so very fine detail comes out as a flat bottomed groove rather than a sharp V.
Your CAM needs to know about the flat, because it changes the depth calculation. Most packages have a flat diameter field for exactly this. If your V-carves come out consistently deeper or shallower than expected, check that field first.
Engraving bits
Small diameter, often very narrow angle, usually with a small flat tip. Sold for fine line engraving and for PCB style work. They are effectively small V-bits and the same geometry applies. They are fragile, they want high RPM and light cuts, and they dull quickly in abrasive material.
Settings for V-bits
Starting point The tip of a V-bit moves very slowly relative to the machine, since it is at the centre of rotation, so conventional chipload maths applies badly at the point and well at the wider part of the cone. In practice:
- Higher RPM than you would use for an end mill of similar diameter, because effective cutting speed at the tip is low.
- Moderate feed rates. Too fast and the point takes a beating in the fine detail.
- Depth is set by the geometry, not by you, on a true V-carve toolpath. What you control is whether there is a flat depth limit.
- A sharp bit matters more here than almost anywhere else. A dull V-bit produces fuzzy, ragged lettering that no setting change will fix.