Bosch 15/64 In. x 3/4 In. Carbide-Tipped Plywood Mortising Router Bit

Why I reached for this bit

I keep a few “plywood-sized” cutters on hand for cabinet work, and the Bosch mortising bit with the 15/64-inch diameter has become the one I reach for when I’m cutting narrow dados and mortises in sheet goods with a trim router. It’s a straightforward, carbide‑tipped, 1/4‑inch shank bit built for the reality of plywood: thin face veneers, abrasive glue lines, and thicknesses that never seem to match their nominal labels.

Setup and first impressions

Out of the tube, the bit looked cleanly ground with even carbide faces and no tool marks on the body. The cutting length is 3/4 inch—plenty for the sort of shallow to mid-depth grooves I cut for dividers, back panels, and shelf supports. The 1/4‑inch shank seats confidently in both my palm router and a full-size router with an adapter collet. Balance matters a lot on small-diameter bits, and this one runs smooth; there’s no perceptible wobble or hum when spun up.

I always check actual cutting diameter with a micrometer before dialing in jigs. This one measured essentially on spec for 15/64 (roughly 0.234 in). That seemingly trivial detail ends up mattering a lot for plywood fit.

Performance in plywood

The bit’s edge geometry feels tuned for plywood rather than solid stock. In practical terms, that means it cuts crisply across face veneers with less tendency to tear the top layer. I ran test passes in maple-veneered cabinet ply and Baltic birch. With a shallow first pass (about 1/16 in) to score the fibers, followed by a couple of deeper passes, the shoulders came out crisp and the floors flat. Any fuzz along the top veneer was minimal and cleaned up with a light pass of sandpaper on a block.

Feed rate is forgiving. At around 18,000–22,000 RPM, a steady push gives clean chips without burning. Push too slowly and, like most straight cutters, it can start to rub in resinous areas of the glue lines; too fast and you’ll hear the pitch change and see slight washboarding. Once I settled into a moderate feed, the cut quality was consistent and chatter-free.

Fit with modern sheet goods

The value of a “plywood-sized” bit is in how it fits real material. Here’s how the 15/64-inch kerf landed for me:

• Domestic 1/4-inch plywood (often 0.20–0.22 in actual): The groove is a hair roomy. For drawer bottoms or back panels that will be captured and glued, I’m fine with that. If you want a friction fit, you’ll likely shim your fence to take a whisper off or consider an undersize bit.

• 6 mm Baltic birch (about 0.236 in actual): Nearly perfect. It’s snug without crushing the plys, which is exactly what I want for divider slots and non-glued friction assemblies.

• Laminated sheet goods with thick face veneers: Still accurate, though I’ll often do a very light climb cut to score the top edge before the main pass to keep the veneer pristine.

In short, this bit shines for metric 6 mm ply and is acceptable for many 1/4‑inch nominal panels depending on your fit preference.

Cut quality, vibration, and control

The bit’s balance translates to easy control, particularly in a trim router where any runout gets amplified. Even in narrow dados, the body tracks without side chatter. I did most cuts with an edge guide and some with a slotting jig; both produced clean, square walls. The bit evacuates chips adequately for a straight cutter—nothing like an upcut spiral, but I didn’t experience chip packing unless I tried to hog full depth in one go. Keeping passes to 1/8–3/16 inch depth made chip flow effortless.

On exit, tear-out is always the test. With painter’s tape over the cut line or a backer board clamped beneath, I had clean edges on both faces. Without either, I saw small splinters on brittle face veneers—more a reality of plywood than a knock on the bit.

Edge life and durability

Plywood is brutal on edges. After routing a handful of 18–24-inch dados and several short mortises—call it 20–25 linear feet total, including Baltic birch—the edge still cut cleanly. No chips or dings, and burn marks were absent unless I paused in one spot. Micrograin carbide seems to be doing its job; it holds up to glue lines better than budget bits I’ve used. I expect to touch this up after another project of similar size, which is about right for a carbide-tipped straight bit in sheet goods.

Where it excels—and where it doesn’t

Strengths:
- Accurate 15/64-inch kerf that suits 6 mm ply very well
- Clean shoulders and flat-bottomed cuts with minimal fuzz
- Smooth running with little vibration, especially in trim routers
- Easy to control in jigs and with edge guides

Tradeoffs:
- 1/4-inch shank flexes more than 1/2-inch shanks in heavy plunges; take lighter passes
- Chip evacuation is good for a straight bit but not on par with an upcut spiral
- The 3/4-inch cutting length caps mortise depth; fine for cabinets, limiting for deep joinery
- For thin domestic 1/4-inch plywood, the groove can be looser than some prefer

If you’re cutting deep mortises in hardwood or want glass-smooth walls in tear-prone veneers, a solid-carbide upcut spiral is still the cleaner (and pricier) option—though you’ll give up the exact plywood sizing.

Practical tips for best results

• Take a scoring pass: 1/32–1/16 inch to sever the top veneer before your main passes.
• Keep passes shallow: 1/8–3/16 inch depth increments control heat and keep walls crisp.
• Dial in RPM: 18,000–22,000 RPM works well for this diameter; adjust to your router’s sweet spot.
• Control the exit: Use painter’s tape or a backer board to prevent chip-out on the far edge.
• Sneak up on fit: For domestic 1/4-inch ply, a fence shim or offset bushing lets you shave the groove to a tighter fit.
• Maintain the edge: Brush off resin, and if you notice polishing on the carbide, a quick cleaning keeps it cutting cool.

Compatibility and use cases

I used it in a compact trim router for most work and in a full-size router for longer dados. The 1/4-inch shank makes it a natural match for small routers—great for on-site built-ins or shop cabinets where portability matters. It’s ideal for:

• Divider slots in 6 mm Baltic birch
• Drawer bottoms and back panels that drop into captured grooves
• Narrow shelf dados in carcass construction
• Mortises for slim hardware or alignment keys in plywood assemblies

It’s less suitable for deep, structural mortises in hardwood or template work where a spiral cutter’s shearing action is an advantage.

Value and alternatives

There are other “plywood-sized” bits that target the same use—some with 7/32- or 1/4-inch diameters depending on the manufacturer’s take on modern ply thickness. In use, this Bosch mortising bit holds its own for edge life and smooth running. If you need even cleaner top edges in fragile veneers, a spiral upcut will win on surface quality but won’t match the dialed-in width for 6 mm and will cost more. For users who primarily work with domestic 1/4-inch ply and insist on a friction fit, pairing this with an undersize companion bit (or a micro-adjust fence) covers all bases.

Bottom line

The Bosch mortising bit does exactly what a plywood-specific cutter should: it runs smoothly, holds an edge through glue lines, and leaves crisp, flat-bottomed grooves sized sensibly for modern sheet goods. It’s a small, purpose-built bit that fits neatly into trim-router workflows and cabinetmaking tasks, and it rewards sensible technique with clean results.

Recommendation: I recommend this bit for anyone doing cabinet or casework in plywood—especially if 6 mm Baltic birch is a staple. Its 15/64-inch cut is a near-ideal match for those panels, and even with domestic 1/4-inch ply, it’s easy to tune a snug fit with technique. If you need a 1/2-inch shank, deep mortises, or the absolute cleanest possible edge in brittle veneers, look to a solid-carbide spiral and accept the tradeoffs. For everyday plywood mortising and dados with a trim router, this bit is a dependable, well‑balanced choice.