How to Cut Slip Tongues with a Flooring Router Bit Kit

By Infinity Cutting Tools | Premium Woodworking Tools ... | Published: 2026-10-31

Category: How-to Guides

Learn how to cut slip tongues for hardwood flooring using a slip tongue router bit kit. Follow the steps for setup, routing, and fitting to get tight, pivot-friendly joints.

Quick answer

To cut slip tongues for hardwood flooring, use a dedicated flooring router bit kit that matches your groove profile, set the bit height precisely, and rout the tongue stock in multiple passes. The goal is a tongue that fits snugly but still lets boards pivot into place without cracking the groove shoulders.

Why the tongue profile matters more than the bit brand

A slip tongue joint works because the tongue is slightly rounded or chamfered, allowing boards to be angled and then pivoted into place. A square-edged spline can bind during that pivot and crack the delicate shoulders of the groove. That is why flooring-specific router bits shape the tongue with relief angles rather than a simple rectangle.

When selecting a flooring router bit kit, check that the bit produces a profile compatible with your groove width and depth. The kit should include bits for both the tongue and the groove if you are starting from raw stock, or at least a matched tongue bit if your flooring already has grooves.

When a slip tongue is the right repair solution

Slip tongues are ideal for repairing or replacing individual boards in an existing tongue and groove floor where the original tongue has broken off or the board must be slid into place. They also work well when making your own flooring from hardwood blanks, especially when you want to avoid the fragile protruding tongue on thin stock.

However, slip tongues are not a substitute for a proper subfloor or acclimation. If the floor is moving due to moisture or structural issues, fixing the joint alone will not solve the problem. Also, if your groove is damaged or inconsistent, a new tongue may not seat correctly.

Step-by-step: cutting slip tongues

Match the bit to your groove: Measure the width and depth of the groove on your flooring boards. Select the tongue bit from your flooring router bit kit that corresponds to that groove size. If the kit includes multiple sizes, test-fit a scrap tongue into a groove before routing your good stock. A tongue that is too thick will split the groove; too thin and the joint will be loose.
Set bit height precisely: Install the bit in your router table and set the height so the tongue is centered on the thickness of your stock. Use a test piece of the same thickness as your flooring and rout a short section. Check that the tongue sits centered and does not protrude above or below the board surface. Off-center tongues cause lippage and weak joints.
Rout the tongue in multiple passes: For hardwood, take light passes rather than cutting the full profile in one go. Start with a shallow cut and increase the bit height or fence position gradually until you reach the final profile. This reduces burn marks and tearout, especially on figured grain. Climb-cutting should be avoided unless you have a power feeder; use a steady feed rate.
Test-fit the tongue in a groove: Slide the routed tongue into a groove on a scrap board. It should fit snugly but slide without forcing. The tongue should allow the board to pivot when angled, which is the key advantage of a slip tongue over a square spline. If the fit is tight, reduce the bit height slightly or use a fine file to ease the edges.
Cut tongues to length and install: Cut the tongue stock slightly shorter than the groove length to allow for expansion. Apply glue to the tongue and groove, then angle the board and pivot it into place. Use a mallet with a scrap block to seat the joint without damaging the flooring. Always leave a small gap at the ends of the tongue to accommodate seasonal movement.

Product facts

Infinity Tools 5-Pc Slip Tongue Flooring Router Bit Kit: This 5-piece kit is designed specifically for making slip tongue joints in hardwood flooring. It gives you the matched profiles needed to cut tongues that pivot into place without cracking groove shoulders.
Infinity Tools 5-Pc Slip Tongue Flooring Router Bit Kit