Router Bits for Wood: Anatomy, Shanks, Types and Bearings

The shank and the collet must match. Bosch's 1617 accepts collets for 1/4 in, 3/8 in, 1/2 in and 8 mm and advises a 1/2 in shank whenever possible. Compact routers take less: Bosch's Colt, DEWALT's DCW600 and Milwaukee's 2723 are all 1/4 in. 8 mm is not 5/16 in: 1/4 in, 8 mm and 1/2 in are not interchangeable, and nor is 3/8 in with any of them. Bosch's Colt manual warns that a bit with a smaller shank than the collet could come loose and become a projectile; Milwaukee warns the collet may break. None of these manuals offers a sleeve or reducer, and none should be improvised: fit the collet made for the shank.

The makers agree on the idea — plenty of shank gripped, the shank not bottomed in the collet, the collet not clamping the curve where the shank meets the cutters — and give different figures for it:

• Bosch (1617 and Colt): insert the shank as far as it goes, back it out until the cutters are about 1/8–1/4 in from the collet nut, with at least 5/8 in of shank inserted.
• Bosch's RA1181 table manual, for a router mounted in it: at least 3/4 in of shank engagement — more than Bosch's own router manual asks.
• Milwaukee (2723): back the shank out slightly to avoid bottoming, leave at least 1/16 in between the collet assembly and the start of the cutting portion, and never clamp a fluted section of the shank.
• Freud, for its bits: at least 80% of the shank in the collet, with its end at least 1/8 in from the bottom.

They are different rules from different makers, so follow both your router's and your bit's; if they cannot both be met, ask the makers before routing. Tighten the nut as your router's manual says. Bosch, DEWALT and Milwaukee all say never to tighten a collet without a bit in it, and Bosch to keep the shank and collet clean. Unplug the router or remove its battery first.

No type is better in general; each suits a cut. Freud describes the three spiral types by the face they leave clean: its up-spiral gives 'the best cut quality on the bottom surface' and clears chips from deep cuts and mortises; its down-spiral suits grooves and dadoes in single-sided veneer and laminate, where the top face matters, and Freud asks for care to keep router and work under control in hand-held and table use; its compression bit combines both shears for clean top and bottom faces in double-sided veneer and laminate.

• Straight bits cut grooves, dadoes, rabbets and mortises along a guide.
• Flush-trim bits have a bearing the same diameter as the cutter: at the tip to follow the layer below, or above the cutter (pattern bits) to follow a template on top.
• Rabbeting bits have a bearing smaller than the cutter; Freud's 32-524 set swaps bearings for rabbets from flush to 1/2 in deep.
• Roundover, chamfer and ogee bits shape an edge, guided by a bearing.
• Dovetail bits have angled sides — Freud's 22-102 is 8° — and work in a jig or on a table.
• Slot cutters cut grooves into an edge on an arbor with a bearing.

Every type is drawn with a Freud example and its figures in the bit profile chart. Dovetail bits in a jig are covered with the joint in dovetails, and the jigs and template guides that steer bits in jigs and templates.

A larger diameter means a lower speed limit. Amana publishes maximum speeds that fall from 28,000 rpm under 2 in to 13,000 above 3-5/8 in for its symmetrical bits, and tells users to check the rating etched on the shank; Freud rates its 1-3/8 in rabbeting set at 16,000 rpm. Freud also says bits over 1-1/2 in diameter must only be used with the router mounted in a table. Taken as written, that rules out hand-held use of its wider bits whatever the job, so check the bit maker's own rule before buying a wide slab-flattening bit for a hand-held router. The makers' figures are compared in the speed chart; a flattening sled that stays within these limits is in router projects.

A set is a collection of profiles, not a quality grade: check that every shank in it matches your collet and that each bit's speed rating is printed. Whether a set or single bits suits the work, and how to read a bit's listing, is covered in choosing router bits. Most of the Freud bits in the chart are carbide-tipped — their pages give a carbide height — while its spirals are solid carbide. Bosch says never to use a dull or damaged bit; Milwaukee warns that a damaged bit can throw carbide. CNC tooling has its own feeds and speeds — Freud says there is no hard-and-fast rule for them — and is not covered here.

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