Making a perfect inlay with a CNC Router

Garrett holds up a finished Feather inlay made with a CNC router

Making a perfect inlay with a CNC Router

Few projects display a woodworker’s skill (and make excellent gifts) like a stunning inlay. And if you’ve ever held an inlay that snapped together with that deeply satisfying click—no gaps, no proud edges, no heart-sinking blow-outs—you know the appeal.

The difference between “good enough” and “perfect” is rarely magic. It’s repeatable geometry, deliberate toolpaths, and a glue-up that favors physics over hope.

Why V-Carve Inlays Work

The V-bit is more than a cutter; it’s self-centering geometry. When you carve a recess with tapered walls and then carve its mirror image on the plug, the two parts try to seat along the whole slope of those walls. That slope is where your precision lives. The fit is not reliant on a perfect perimeter offset; instead, the depth values control exactly where the two parts meet. This is why inlay recipes are written in terms of start depth and flat depth rather than “leave 0.2 mm on the line.”

In other words, you engineer the friction into the Z-axis, rather than gambling it away in XY. That’s the core lesson here.

Bit angle governs two things: detail resolution and mechanical wedging. Sharp matters more than fancy. A fresh V-bit cuts clean edges and preserves pointy details. A 60-degree V-bit reaches deeper for a given line width, which can help tiny serifs and sharp corners hold together.

A 90-degree V-bit is less aggressive and often friendlier for larger graphics, where fine needle points aren’t at risk. You can achieve impeccable inlays with either; the key is to keep the angle consistent across the female and male operations and choose feeds and speeds that avoid chattering those delicate apexes.

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Harder, tighter-grained species are our allies here. Maple on walnut is the classic demonstration pair because the contrast is high and the fibers don’t crumble at the edges. Open-pored or very soft woods will still work, but they reduce the margin for tiny chips during machining and cleanup. If you’re new to inlays, don’t complicate things: choose cooperative wood, a sharp V-bit, and a design without hair-thin spokes for your first run.

Depth Strategy

Successful inlays lean on a two-part depth recipe. The female pocket uses a start depth that’s usually zero and a modest flat depth that establishes the maximum width at the pocket rim.

The male inlay uses a start depth greater than zero, which virtually lifts the carving plane and makes the male a touch smaller up top but deeper down its taper, so it keys into the female and stops on the slopes before bottoming out. The flat depth of the male creates the land that will remain proud before flush-trimming.

There isn’t a single sacred pair of numbers because different bit angles, materials, and design scales change the geometry. That’s why makers present their settings as examples, not commandments.

For instance, some craftspeople achieve excellent results with a 90-degree V-bit, using a shallow female flat depth of around a tenth of an inch and a male that begins just below that start depth, finishing with a very small flat depth to create a thin, trimmable shoulder. The underlying idea is to make the male “reach past” the female’s wall intersection in Z, then trap it there with glue and clamping pressure.

First, sketch the V-bit as a triangle and mark your female flat depth; that sets the recess width at the top surface. Next, choose a male start depth that drives the male walls slightly deeper than the point where your female walls meet. This guarantees interference along the slope, which is what you want.

Finally, give the male a small flat depth so you have a micro-ledge to plane or sand away after glue-up. If you can visualize those two triangles interlocking with a thin horizon of “extra” stock above the pocket, you’ve got the puzzle solved (in principle, at least).

Toolpaths to Protect the Edges

A desktop view of the files for a feather inlay in vector software for CNC machine

Chipping at the mouth of a V-carved pocket is the usual way a perfect inlay becomes a “clever save.” A reliable way to reduce that risk is to run the V-carve portion before the clearance pocket.

Let the V-bit define the crisp walls, and then use a small end mill to evacuate the floor to the desired female flat depth. This sequence keeps the fragile rim from being undercut by a flat bit that might pluck out end grain. Many experienced inlay makers adopt that order regardless of software, precisely because it preserves the geometry on which the inlay depends. You’ll see the same spirit of edge-protecting passes in other respected tutorials on the subject.

On the male, avoid removing every last island of support around hair-thin details. If a tiny internal point is essentially a wooden needle, it will be strongest while it’s still attached to extra stock. When possible, cut the male from a blank that you can keep thicker during machining and only profile free right before glue-up, or even after, if your workholding allows it. That way, the fragile features spend less time as naked geometry and more time supported by the parent stock.

Workholding, registration, clamps, and the fit

A perfect inlay doesn’t survive a sloppy clamp. For repeatability, work inside a simple spoilboard fixture with two straight fences meeting at a square corner. Pin both female and male blanks into that corner with the same X/Y zero, and let your Z be the only variable that you change between toolpaths.

You’re trying to eliminate “surprises of translation.” If your CAM relies on a datum at the lower-left corner, your fixture should make that corner stupidly easy to repeat. A calm setup pays bigger dividends than any micro-tweak to depths.

For those using vacuum, check that the gasket or tape doesn’t compress unevenly on the plug; even a degree of tilt across a long inlay can telegraph as a hairline gap. For manual clamps, use cauls and a sacrificial layer to clamp closer to the design without denting the surfaces that matter.

A slow-set PVA, or a wood-friendly epoxy if you need gap-filling or a longer open time, are both excellent choices. Whichever you choose, spread it to cover the pocket walls as well as the floor. Those angled walls are your contact surfaces; starve them and you starve the fit. Press the male in by hand first and watch how it slides; if it bottoms immediately, your male start depth likely needs to be deeper next time. If you feel a long, even resistance that tightens as the top approaches the work surface, that’s the geometry doing its job.

Clamp with conviction but not with panic. You want firm, even pressure that seats the entire perimeter at once, not a sequence of point loads that flex the plug. Many makers prefer to see a faint, uniform glue squeeze at the mouth, then leave the piece alone rather than re-torquing clamps five minutes later. Patience wins here. The “perfect” feeling comes from alignment and curing, not from violence.

Flush-Trimming

A CNC router shaves a feather inlay flush

After the cure, remove most of the proud material with a trim plane, a sharp card scraper, or a wide sanding block. A router-mounted surfacing pass is tempting, but it’s far too easy to telegraph a divot if the base straddles unsupported areas. The safest approach is hand-driven and boring. This is the least glamorous part of inlays and the one that ruins the most good work.

Take your time. When the last whisper of the male’s flat is level with the surrounding field, then—and only then—switch to orbital sanding and sneak up on your sheen.

You’ll know the geometry was proper if you can’t slide a fingernail into the perimeter. You’ll know your workholding was right if the grain runs where you intended, the points are intact, and nothing walked as it cured.

Software

Vectric, Carbide Create, and other CAM suites have differences in how they operate, but the woodworking principles remain constant: set the female with a small flat depth, set the male with a deeper start depth than the female’s flat, and provide the male with a thin flat for trimming. That’s the backbone of perfect inlays, whether you’re following IDC Woodcraft’s method or others that show the same geometry with slightly different numbers.

Troubleshooting

Microscopic gaps at a few corners almost always trace back to one of three culprits: a dull bit that broke fibers at the rim, a male start depth that didn’t reach far enough to create true interference along the wall, or tiny deflection when clearing the pocket after the V-pass.

The fastest remedy is a tiny bump to the male start depth on your next run, combined with a brand-new V-bit and the “V-first, clear-second” toolpath order. Don’t overlook humidity, either. If your plug wood has a higher moisture content than your pocket wood and then dries after glue-up, you can produce a hairline on one side even when the geometry is right. Let your stock equalize in the shop for a couple of days before you cut.

When fragile tips are missing, slow the feed for the last finishing pass with the V-bit and consider choosing a species with tighter grain for the plug. If a large, flat region of the male sits proud after full clamping, that’s a sign the male bottomed on the floor rather than seating on the walls; next time, deepen the male start depth or reduce the female flat depth so the stop lives on the taper, not the basement.

Design choices and your first project

Inlays love confident shapes. If you’re pulling your first test, pick a motif with crisp transitions, clean on-curves, and no feather-thin terminals. Circular arcs and beveled serifs show off what V-carving does best: unbroken lines that meet at clear intersections. If you must include wispy details, give them a bit more stroke weight than your 2D designer’s eye prefers. The wood will thank you. As your results become consistent, you can dial those strokes back down, and the geometry will carry you.

Contrast matters as much as precision. Walnut filled with hard maple looks great because your eye reads the seam as a design element, not a defect. Mahogany on cherry, by comparison, can be so subtle that it hides your craftsmanship from anyone standing farther than arm’s length. If this is a gift, err on the side of visible.

If you’ve never tried a V-carve inlay, the most productive way to learn is to do a scale rehearsal. Mill two coasters from offcuts and cut the same simple emblem at coaster scale. That miniature dress rehearsal teaches you everything that matters—the way your bit behaves, how your clamping feels, whether your start and flat depths are generous or stingy—without committing a $60 board. After a single rehearsal, the mystery evaporates, and you’ll approach the full-size panel with the calm of someone who knows how the triangles will meet.

There’s no hidden trick in creating the perfect inlay. It’s simply a tiny handful of deliberate decisions anyone can repeat. Keep the geometry consistent, protect the edges, let the walls seat the fit, and don’t rush the trim. If you internalize those moves, the perfect inlay is no longer a miracle: It’s your shop’s new default.

Be sure to check out IDC Woodcraft’s free beginner’s CNC kickstarter guide. For those who want to try their hand at the feather inlay project in the IDC Woodcraft video above, click here for the instructions and g-code files.

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