Choosing a Birdsmouth Router Bit for Joinery
By Premium CNC & Router Bits for Precision Cutting | Published: 2026-10-18
Category: Buying Guides
Learn how to choose the right birdsmouth router bit for your joinery project. Compare 6, 8, and 16 side options for poles and multi-sided assemblies.
Quick answer
Choose a birdsmouth router bit based on the number of sides your project needs: 6 or 12 sides with the Whiteside 3506, 8 sides with the Whiteside 3508, or 16 sides with the Whiteside 3516. All work with a router table and fence on stock up to 7/8" thick.
How birdsmouth bits create strong joints
A birdsmouth router bit cuts a V-shaped notch along the edge of a board. When you run matching edges through the bit, the notches interlock to form a tight, glue-ready joint. This method is especially useful for building multi-sided columns, poles, and tapered legs without complex jigs.
The key difference between models is the number of sides they produce. The bit's geometry determines the angle of each notch, which directly controls how many boards you can join into a closed polygon. More sides mean a shallower angle and a smoother overall shape.
Stock thickness matters
All three Whiteside birdsmouth bits accept a maximum stock thickness of 7/8". If your material is thicker, you will need to plane it down or choose a different joinery method. The large 1-3/4" to 1-7/8" diameter of these bits also requires a router with enough power and a stable router table setup.
Shank size and compatibility
Each bit uses a 1/2" shank, which provides good stability in a router collet. Make sure your router accepts 1/2" shanks; some compact models only take 1/4". The larger shank reduces vibration and helps maintain a clean cut across multiple passes.
Decision rules for choosing a birdsmouth router bit
- Count the sides: Decide how many facets your finished piece should have. 6 sides work for hexagons, 8 for octagons, 12 or 16 for nearly round shapes. The bit you choose must match that number exactly (or a divisor, like 6 for 12).
- Check your stock thickness: Measure your material. All three bits max out at 7/8" thickness. If your boards are thicker, you must resaw or plane them down before routing.
- Verify router compatibility: Confirm your router has a 1/2" collet and enough power (at least 2 HP recommended) to spin a large-diameter bit safely. A router table with a fence is required for consistent results. Always do a test cut on scrap material to confirm the joint fit before working on your final pieces.
Birdsmouth router bit options
- 6 or 12 Side Birdsmouth Router Bit – Whiteside 3506: The Whiteside 3506 cuts notches for 6 or 12 sided projects. It has a 1-7/8" diameter and accepts stock up to 7/8". Choose this bit if you need a hexagonal column or a 12-sided shape with shallower angles for a more rounded profile.
6 or 12 Side Birdsmouth Router Bit – Whiteside 3506 - 8 Side Birdsmouth Router Bit – Whiteside 3508: The Whiteside 3508 cuts notches for 8 sided projects. It has a 1-3/4" diameter and accepts stock up to 7/8". This bit is ideal for octagonal poles or tapered legs where an 8-sided shape gives a good balance of strength and appearance.
8 Side Birdsmouth Router Bit – Whiteside 3508 - 16 Side Birdsmouth Router Bit – Whiteside 3516: The Whiteside 3516 cuts notches for 16 sided projects. It has a 1-3/4" diameter and accepts stock up to 7/8". Use this bit when you want a nearly round pole with many facets, reducing the amount of sanding needed to achieve a smooth cylinder.
Which birdsmouth bit is right for you?
Best for
- Building hexagonal or dodecagonal columns with the Whiteside 3506
- Creating octagonal poles or legs with the Whiteside 3508
- Making nearly round, multi-faceted poles with the Whiteside 3516
Not for
- Projects using stock thicker than 7/8" without planing
- Joinery that requires hidden fasteners or metal brackets
- Routers with only a 1/4" collet
