Setting Up Adjustable Tongue and Groove Bit Sets

This setup procedure is simple and easily repeatable. Click image to enlarge

Perfection and repeatability

Text & Photos by Tom Hintz

   Setting up tongue and groove bit sets is easy, especially after going through the process a time or two. The primary concerns are the alignment of the joint itself, including the faces of the boards being joined and the final dimensions of the three primary features, the tongue and the shoulders above and below the groove. While having all three features equal in thickness is ideal, that depends greatly on the thickness of the material. For most home woodworkers, ¾"-thick wood is most common and works well with these cutters. It is also the maximum useable thickness for most tongue and groove sets. All examples throughout this story use ¾"-thick wood.

   The bit set used for this article is the Infinity #61-502 Tongue and Groove Bit Set, with ½"-shank. The basic design of the Infinity set is very similar to many other tongue and groove sets on the market and this setup procedure will work with most of them as well. If the instructions that came with your bit set differ, use those instructions.

   Hint: Marking the top face of all test pieces and making the cuts with that side up will make it easier to identify which way cutter height must be changed to effect a correction.

   Note: A common method for setting up tongue and groove bits is to set the grooving bit close to center and then make two cuts, flipping the board over between them to actually center the groove.

Setting the fence flush with the bearings insures correct dimension of the tongue and groove. Click image to enlarge

While this works, the thickness of the tongue can vary substantially, which makes repeating the setup very difficult. The process described here takes a little longer the first time but allows repeating the setup later much faster.

Setting the Fence

   Both of the Infinity bits feature depth-limiting bearings, installed at the factory. Using a straight edge, set the face of the fence flush with the bearing on both bits. This automatically controls the depth of the groove and the corresponding length of the tongue so they fit properly when assembled.

Setup the Grooving Bit First

   Use a piece of scrap the same thickness as the work material and large enough to cut a groove in safely. Set a small combination square to slightly under ¼" and draw lines on the edge of the scrap from both sides near an end. This “bracket” gives you an easy to use “sight picture” that helps get the bit centered on the wood the first time.

Using two lines rather than one for centering the bit is far more accurate. Click image to enlarge

   Lay the wood on the router table and adjust bit height so a cutter is centered between or on the two lines.

   When satisfied with the adjustment, set the fence and make a cut down one edge of the scrap. Shut the router off, flip the board over and set it against the cutter again. If the cutting edge slips into the groove with the board inverted, the bit height is correct and the groove is centered.

   If the groove will not slip over the bit, look to see where it is hitting the sample. If the top edge of the cutter is catching on the shoulder (the board still upside down), the bit was too high. Lower the bit an amount equal to one-half of the amount of error you see.

   For example, if the top edge of the cutter is 1/8" above the groove, lowering the bit 1/16" should correct it. Using an un-cut edge of the scrap, make another cut at the new setting, shut the router off, place the wood against the cutter (upside down) again and check it to confirm the setting.

Infinity adds a stack of washers to the tongue bit for adjustment. Click image to enlarge

   When satisfied with the setup, cut a piece of the final test piece to use as a setup gauge when this bit set is used in the future. To use the gauge, lay it on the router table and adjust the groove bit height so the cutting edges slip into the groove. A quick test cut in scrap to confirm the setup should be all that is needed.

Setup the Tongue Cutter

   The Infinity tongue-cutting bit comes with a stack of 0.0295"-thick washers, used to adjust the space between the twin cutting blades to control the thickness of the tongue. Note that when taking the top cutter off the shaft, there is a bronze-colored washer between it and the bearing. This washer must be against the bearing at all times. Any spacing washers installed below the upper cutter go on top of the bronze-colored one.

The cutter edges should align flush with the edges of the groove. If they do not, shim the upper cutter until they do. Click image to enlarge

   First, install the tongue cutter bit in the router table with both cutters installed and the nut snugged down. Lay the groove gauge block (made earlier) on the router table next to the bit and adjust the bit height so the top edge of the lower tongue cutter is flush with the bottom edge of the groove. If the top cutter is not even with the upper edge of the groove, note the amount of error and install enough spacer washers below the cutter to raise it that amount.

   With the nut secured on top of the tongue cutter, align it to the groove gauge block again to check the alignment. When satisfied with the alignment visually, cut a tongue in a piece of scrap the same thickness as the project wood.

   Test the fit of that tongue into the groove gauge block and make adjustments to the spacing washer configuration as needed

Taking the time to cut setup blocks will save far more time when this bit set is used again. Click image to enlarge

for the tongue to fit the groove. The tongue should slip into the groove without much force to allow room for glue and expansion/contraction cycles.

   If the tongue fits the groove properly but the faces are out of alignment, adjust bit height to compensate.

   When satisfied with the fit and alignment of the faces, make a cut in a fresh piece of scrap and save it as a gauge block to be used in the future for setting up the tongue cutter bit.

   That’s all there is to it! After using the tongue and groove bit set a few times the setup goes very quickly. Another benefit of this procedure is when making additional tongue and groove stock of the same thickness, this setup will produce new pieces that fit existing stock correctly.

   Take your time, use scrap wood that is the same thickness as the wood to be used in your projects and all will go fine!

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