Determine the width of each flooring piece you will need to cut. Either measure the width of any existing flooring boards with a tape measure so you can match the new flooring to it, or measure the width of the room you will be laying floor in, measure the width of your hardwood and divide the floor width by the hardwood width. Add 1/4 inch to this width to find the width to cut your wood to.
Set the fence on the table saw to the width you want to cut. Hold the wood against the saw fence and run the wood lengthwise through the table saw to cut it to the correct width. If the wood is not straight on both sides, set the fence width a little wider than needed and cut both sides of the wood, setting the width correctly for the second side, to straighten the flooring piece.
Measure the depth of the groove on the existing wood, if there is any, or measure the thickness of the flooring and divide it by 3 to determine a new groove depth. Set the fence to the groove depth. Set the height of the saw to the width of the flooring. Run the wood through the sawmill on its side to cut one side of the groove.
Turn the wood around and run it through the sawmill again to cut the other side. Cut out the middle of the groove with a chisel to form the groove. Turn the wood over so the grooved edge is facing down. Cut two lines through the wood again.
Set the fence to the groove depth. Lower the saw height to the groove depth. Run the wood through on both sides to cut away the excess wood to leave a notch for the groove. This notch will fit into the groove on the flooring beside it, allowing the flooring to interconnect.