Chapter 7

Some Jointing

    Now that I've got these pieces close to their final shape, I can start cutting the mortise and tenon joint that will hold them together.  This is not quite your typical M & T joint, with respect to the fact that it will need to be a bit looser than one would normally try to cut, and it will receive no glue.  In keeping with the traditional methods Celtic Harpmakers used, the main components of the harp will fit nicely together, but it will be only the string tension that will hold it all together.  Also, this pillar is going to have to lean to the players right slightly, where the bottom of the pillar will be centered on the harp base, the top of the pillar will be to the right of center.  To accomplish this, the tenon must have a little bit of side to side play within the mortise.  This will become clearer later.  Here I have positioned the pieces over my full size drawing, to establish their relationship to each other, and am marking the position of the mortise on the inside face of the right half of the neck.  I have also marked the shoulder of the tenon on the underside of the pillar. 

    Here I have taken the pillar over to the workbench and laid out the cut lines for the cheeks and shoulders of the tenon.  The tenon measures 3/4" wide, 1" long, and will penetrate the neck to a depth of 1 & 1/8" when complete.  The shoulders will be square at this stage, but later, just before final assembly, they will have to be hand carved to mate with the curved surface of the neck at the slight angle that is going to be generated.

    Here all 4 cheek cuts have been cut by hand with a tenon saw.  Next I'll lay the piece down and cut the four shoulders, removing the waste.

    The shoulders of the tenon are still a bit rough here, but I'm not going to spend any time on them right now.  As I said, these will have to be fitted to the neck later anyway.  You can see the curved line below the right shoulder that represents the curvature of the neck  At this point in construction, this is good enough.

    I returned to the plan, re-positioned the pieces, and marked the size and location of the tenon on one half of the neck.  After clamping the neck securely to the bench, carefully chisel out the mortise half as deep as the tenon is wide, and 1/8" longer than the tenon. Remember that later when you fit the pillar to the curvature of the neck, the tenon is going to penetrate the neck a little bit deeper than it does in it's current configuration.

    Once I've got the first half of the mortise chiseled out nicely, I position the two halves of the neck together, and transfer the location of the mortise to the second half of the neck.  Then back to the workbench for more chiseling.

    A moment of truth here, and success!  The pillar fits very nicely, with the exception of the square shoulders up against a convex surface.  The pillar has very little movement in the mortise in the front to back direction, and just enough side play to allow for the angle that will be needed.

    Now I can finally glue up the two halves of the neck.  This piece has to be able to withstand an incredible load with the tension of all of the strings, so I was extra careful to be sure to get a really strong glue joint here.  I spread glue over the entire inside faces of the two halves, and used plenty of clamps to ensure a good bond.  I was relieved to observe just the right amount of glue squeeze-out along the entire length of the seam.

That's enough for today, I want to let this assembly set for at least 24 hours before I release the clamp pressure anyway. 

Until next time.

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