Choosing the Right Router Bit

Most router bit problems are selection problems, not technique problems. A bit that burns, chatters, or tears grain is usually the wrong bit for the material, the machine, or the cut. Here's what actually matters on the spec sheet.

Start with the Shank

The shank is the shaft that goes in the collet, and it is the least forgiving spec on the page.

• 1/2" shank — four times the cross-sectional stiffness of a 1/4". Use it whenever your router accepts it, especially for large-diameter profile bits and anything taking a deep pass.
• 1/4" shank — fine for small trim and edge work, and often the only option on compact and trim routers.

Match the bit to the collet you actually have. Improvised adapters and sleeves are a good way to lose a bit at speed.

Carbide Grade and Construction

Nearly everything worth buying is carbide-tipped or solid carbide.

• Carbide-tipped — a steel body with brazed carbide cutters. The standard for profile and edge-forming bits. Look at the thickness of the carbide: more material means more resharpenings before the bit is done.
• Solid carbide — the whole cutter is carbide. Standard for small-diameter spirals and anything where a brazed tip would be too bulky. Stiffer and more brittle; it does not like being dropped.

Micrograin carbide holds a finer edge and is worth the premium in hardwood and abrasive sheet goods like MDF and melamine.

Geometry: Where the Chips Go

For straight cuts, the flute direction decides which face stays clean.

• Up-cut spiral — pulls chips up and out of the cut. Best chip evacuation, best for deep slots and plunge work. Tends to tear the top face.
• Down-cut spiral — pushes chips down. Leaves a clean top edge, which is what you want on veneered plywood and laminate. Packs chips into a deep slot, so take lighter passes.
• Compression — up-cut at the tip, down-cut above it. Leaves both faces clean. The right answer for double-sided plywood and melamine, and priced accordingly.

Diameter and Pass Depth

A larger-diameter bit removes more material per pass but runs faster at the rim, so it needs a lower RPM. As bit diameter climbs, drop your router speed — a large panel-raising bit belongs at the bottom of your speed range, not the top.

Rule of thumb for pass depth: no deeper than the bit diameter in softwood, and lighter than that in hardwood. Burning is more often a sign of too slow a feed rate than too fast.

Bearings

Bearing-guided bits are only as accurate as the bearing. If a flush-trim bit is leaving a step, check the bearing for play before you blame the cutter — bearings are a replaceable wear item and cost a fraction of the bit.

Before You Order

Check three things against your machine: the collet size, the maximum bit diameter your router or table will clear, and the RPM range. If a bit's rated maximum speed is below your router's fixed speed, it is the wrong bit for that machine.

Not sure which one fits your setup? Send us the machine, the material, and the cut, and we'll point you at the right bit.