Q: I'm using some 2-inch-thick lumber to make kitchen work tops. This wood has some defects, like knots. I cannot figure out how to use my hand router to cut out these defects in a curved cut and then end up with two tight fitting pieces. Any pointers to find which way to do this would be much appreciated.

A: Indeed, if you cut out defects in lumber and then glue it back together and if the cutting pattern is curved (sometimes called a serpentine cut), the joint will be nearly invisible. In fact, the US Forest Service laboratory in Princeton, W. Va., carried out a lot of experimental work on this technique 15 years ago. It is really amazing how this technique effectively hides the end joints.

What you are trying to do is very tough to do in one pass of a hand router. Here is why.  If you carefully sketch out the path of the router when traveling on a curve, you will see that the outside radius is different than the inside. As a result, after the router has made a curved pass and removed the defects, the two ends created will not fit together tightly; there will be a gap in the middle of the curve. If you had a numerically controlled router, you would program in the dimensions and it would cut the same radius on both ends using two passes.

If you are willing to put in the time, here is a list of steps to do the job with a hand router. After cutting out the defect with the router using a curved path, take the end of one piece and draw the approximate shape of this end on an appropriate sized piece of stiff transparent plastic, making a pattern. Cut out this pattern and double-check to make sure it fits snugly into the first piece of wood. Attach this plastic pattern piece to the end of the second piece of wood and use it as a guide for the router. Rout the end of the second piece. If this second piece fits tightly into the first piece (which it should), glue it in place. 

As this involves a lot of work, I think you should consider either purchasing a numerical controlled router (tremendously useful machine) or else "farming out" this job to someone who has one.