same bit can be used to cut both pieces of joint
put boards together for tongue and groove joint
Use a Straight Flute Bit to Cut the Joint (Optional)
Specialty tongue-and-groove bits make easy work of creating the joints, but they can be a bit expensive. If you don’t have the budget for those bits, a simple straight flute bit can be used to cut a tongue-and-groove joint. The same bit can be used to cut both pieces of the joint. Cut the groove first. Set the fence on the router table so that the bit will cut approximately through the center of the board. Turn the board around and make another pass. The board now has a cut through the center. For the tongue, move the fence forward so that you’re cutting away the edges of the board. Your goal is to leave the same amount of material on the tongue board as you cut away on the groove board. This will take at least two passes. Once the cuts are made, put the boards together to get a tongue-and-groove joint.