When readying parts to be edge glued, most of us probably trust the surface left after a pass over the jointer knives as being smooth and ready for gluing. After all, it feels smooth, and when the boards are placed edge to edge the fit looks pretty darn good. We don’t see how the fit could be much better and we forge ahead, slop on some glue and clamp the pieces together until we think we’ve pressured them far enough into submission such that they will yield a seamless joint. I know I’ve been down this road – and sometimes the joints are fine, but sometimes they are less than perfect.
I was working with some pieces of Walnut today and nearby there was some white chalk on the bench that I was using for marking out parts on the dark wood. The pieces I was working with were about 2 inches thick and 8 inches long and I needed to edge glue them. As is the norm, I held two of the pieces together edge to edge and inspected the joint it offered after a pass over the jointer knives – it looked OK, but not perfect.
I spotted the chalk again and thought maybe I should see just how good that jointed surface was. In the pictures you can see the surface of one of the boards after rubbing the edge lightly with the white chalk (the second one is a close-up of the same board). You can clearly see the uneven surface left by the jointer. As you can see, the rotating knives of this tool leave little scallops on the wood surface – in fact the width of these scallops changes depending on how fast the piece is moved over the knives. The slower you go, the closer together the scallops are and the better the resulting surface – better yes, but not perfect.
After seeing this, I felt I could make the surface better. I don’t have a jointer plane, so, I pulled out my #4 smoothing plane to see what I could do. I made a few passes along the edge of the board watching as the plane removed the white chalk leaving a stripe of chocolate colored wood in its wake. The first picture is the resulting surface (the second picture is a close-up of the hand planed edge). I put some Naptha on a paper towel and wiped away the residual chalk that was still in the pores of the wood. The smoothing plane only removed one or two thousandths of an inch of material, however, as seen in the pictures, the surface quality was now infinitely better.
I often use my smoothing plane on the faces of panels and other parts that have been face jointed in order to remove these milling marks. However, I don’t always edge joint with a hand plane after using the jointer. My edge-glued joints are usually pretty good but, I sometimes think that they can be better. After this little experiement, I’m sure of it. Of course, a smoothing plane is not the best tool for this job…so, it looks like I’ve got a good reason for a jointer plane to be the next entry in my hand tool arsenal!