How-to
How to Make V-Carve Inlays on a CNC Router, Step by Step
V-carve inlays look like they took a master woodworker days to make: a walnut monogram set perfectly into maple, with crisp points and no visible gaps. On a CNC router, they're very achievable once you understand how the two halves fit together.
This guide explains how the technique works, how to set up the toolpaths in general terms, and the mistakes that cause gaps or a part that won't seat. Settings names vary by CAM program, so check your software's documentation for the exact fields.
How V-carve inlays work
A V-bit makes a groove with sloped walls. If you carve a design into one board (the female) and carve its mirror image as a raised shape into another board (the male), the sloped walls match. Push the male into the female and the walls wedge together, which is why V-inlays close up so tightly.
The trick is that the male mustn't bottom out before the walls meet. So the male is carved as if it started a little below the surface (the start depth), and the female is carved slightly deeper than the male will seat. When you press them together, the sloped walls contact first and a small gap remains at the bottom, which fills with glue. The wedge effect closes the visible edge.
Why the V-bit matters
Both halves must be cut with the same V-bit angle. If the female uses a 60-degree bit and the male a 90-degree bit, the walls won't match and you'll see gaps.
Choosing woods and supplies
Wood combinations
Contrast is what makes inlays pop. Popular pairings include walnut into maple, maple into walnut, cherry into maple and padauk or other colorful species into a light base. Choose woods that are:
- Stable and dry, so the joint doesn't open up after it's finished.
- Close-grained enough to hold sharp points. Very open-grained woods can chip at fine tips.
- Similar in hardness, where possible, so planing and sanding don't dish the softer one.
Thickness and flatness
Both boards must be flat. The male board needs to be thick enough for the carved plug plus a little backing to hold it together during glue-up. A cupped board won't seat evenly and gives you gaps in the middle or at one end.
Supplies checklist
- A sharp V-bit (a 60-degree bit is a common choice for inlays, but use what your CAM and design suit)
- A small flat end mill for clearing large flat areas, if your design has them
- Contrasting hardwood stock, flattened
- Wood glue with enough open time to assemble
- Clamps or a press, plus cauls to spread pressure
- A band saw, table saw or planer to remove the excess male board
- Sandpaper or a card scraper for final flush-up
Designing for inlay
- Bold works better than delicate. Very thin lines and tiny serifs are hard to inlay cleanly. Start with bold fonts, simple monograms and clean shapes.
- Closed vectors. Every shape must be a closed vector. Open curves won't carve correctly.
- Mirror the male. The male plug is the mirror image of the female, since it will be flipped face-down. Many CAM programs handle this in their inlay workflow, but double-check before cutting.
- Large flat areas. Wide shapes get deep fast with a V-bit. Use a flat-depth setting with a clearing bit to limit the depth on both halves.
Key settings: start depth, flat depth and gap
Names differ between programs, but the same settings show up:
| Setting | Applies to | What it does |
|---|---|---|
| Flat depth (pocket depth) | Both | Limits how deep the V-bit cuts; a flat bit clears wider areas |
| Start depth | Male | Carves the plug as though the surface were lower, so it seats deeper into the female |
| Glue gap | Result | The space left under the plug when seated, for glue and to stop it bottoming out |
| Extra depth / clearance | Male | Additional clearance cut around the plug so the backing board doesn't hit the base |
In general terms, the start depth controls how far the plug can sink into the pocket, and together with the two flat depths it sets how much gap is left underneath. Your CAM's inlay tutorial will give a starting combination and explain how its fields relate. We're not going to give universal numbers because the right values depend on your bit, design size and machine accuracy.
Test on a small design first
Make a small test inlay, maybe a single letter, in scrap of the same woods. Check the fit by pressing the halves together dry (with no glue). If the plug won't go in far enough, adjust; if it's loose, adjust the other way. Write down the combination that works for your bit and machine.
Step-by-step process
- Flatten both boards and mark their faces. Any warp shows up as gaps.
- Carve the female in the base board with your V-bit (and clearing bit if using flat depth). Keep the base board clamped flat across its full width.
- Re-zero carefully between bits. If the clearing bit and V-bit are zeroed differently, the depths won't match. Use a touch plate and zero both bits from the same surface.
- Carve the male in the inlay board with the same bits, using your start depth and mirrored design. Include the clearance pocket around the outside of the plug if your CAM provides one.
- Test fit dry. Press the male into the female by hand. It should go partway and stop on the walls. Don't force it all the way, or you may not get it out again.
- Glue up. Apply glue to the walls of the female (and lightly to the male). Align, then press it in.
- Clamp. Use cauls and even pressure across the design until the plug seats. Too much glue in one spot can hydraulically block the plug from seating, so spread it evenly.
- Let it cure fully, following the glue manufacturer's time.
- Remove the excess. Cut most of the male board off with a band saw, then plane, sand or surface it flush on the CNC. Many makers surface it with a flattening bit on the CNC for a controlled finish.
- Sand and finish. Sand evenly through grits and apply your finish.
Troubleshooting common problems
| Problem | Likely causes | Fix |
|---|---|---|
| Visible gaps around the edges | Plug bottomed out before walls met; boards not flat; different V-bit angles | Increase the glue gap; flatten stock; use one bit for both halves |
| Plug won't seat | Glue gap too small; chips or dust in the pocket; too much glue | Adjust start depth; clean the pocket; thinner glue layer |
| Broken sharp points | Dull bit; brittle or open-grain wood; design too fine | Sharp bit; better wood; bolder design |
| Inlay disappears after flushing | Sanded or planed past the depth of the inlay | Check how much material is left; remove excess gradually |
| Gap only on one side | Misalignment; Z zero differs between bits | Careful alignment; consistent zeroing |
Finishing tips
Sanding dust from dark wood can fill the pores of a light wood, muddying the contrast. Vacuum between grits, and some makers seal the surface lightly before final sanding to help. When you apply finish, a light first coat lets you check the inlay before building up.
Safety
Inlay work involves V-carving, surfacing and often band saw or planer work. Wear eye and hearing protection, collect dust at the source (some exotic woods are known irritants), and stay with the CNC while it runs.
FAQ
Do I need special CAM software for V-carve inlays?
Many popular CAM programs that do V-carving have a built-in inlay workflow or tutorial. Check whether your software supports start depth or a dedicated inlay option.
What V-bit angle is best for inlays?
Many makers use a 60-degree V-bit for inlays, but other angles work as long as the same bit cuts both halves. Follow the guidance for your CAM software.
Can I inlay into plywood?
You can, but the plies show in the walls of the carving and can chip. Solid hardwood gives much cleaner results.
How do I avoid sanding dust staining the light wood?
Vacuum between grits, avoid aggressive sanding, and consider a light sealer coat before the final grits.
How long should I wait before flushing the inlay?
Follow the cure time on your glue's label. Cutting or planing too early can break the joint or pull the plug out.
Bottom line
Our take
V-carve inlays come down to three things: matching V-bits, flat stock and the right start depth and glue gap for your machine. Do a small test first, write down what works, then scale up to signs, boxes and cutting boards. Bold designs in contrasting, stable hardwoods give the best results.
If you're getting started, pair a sharp 60-degree V-bit with a few contrasting walnut and maple boards and practice on a single letter.