Hi Jim and Ed - Well, the topic (thanks to me, I guess) is going off course, but what else is new?
Both of your approaches sound as if they have positive aspects. Ed, your method of final fitting of the shims, in particular, sounds like something I would like to try. Thanks for your input. Chuck
Greetings,
Thanks for the note, Chuck. I have begun another thread, (or fuse, as the case so often becomes…)
A couple of other things I didn't mention. If the board is to be refinished, I do the shimming before I remove the finish from an old soundboard, using the finish to protect the wood from glue staining. I usually put a strip of masking tape on either side of the crack, as close to the edge of the routed "V" as possible. This allows me, as Ed M. does, to use a sharpened chip to scrape the glue off the sides of the exposed shim without it ever touching the board. This saves my chisel edges some wear and tear. Then the tape comes up and there is no glue, anywhere.
I have, though, often shimmed boards and kept the old finish if it was pretty. Bill Garlick taught us this technique in case we had some historical considerations. I also have run shims right through the decal, and it is really tricky cutting them flush without damaging the edges of the decal. It can be done. Older Steinway boards have shellac, which is easily cleaned and repaired.
Craftsman once sold 1/16" veining bits. I bought a bunch of them and cut spruce to match the angle. If I need a wider shim, I grind off the ends of the bits so that it can cut a wider gap without cutting the ribs as I pass over them. If using a router against a straight-edge, the same effect can be had by dropping a thin ruler or hack-saw blade between the router base and straight-edge on the second pass to widen the crack with the same bit.
These bits will leave a routed, tapered end to the crack, which is easily duplicated on the shim. It is important to leave enough clearance on these ends so that as the shim sinks into the crack, it doesn't bind end to end, preventing firm seating in the crack. Done exactly right, the only clue there is a shim installed is the small line between grain lines that the joint crosses at each end where the edge of the shim crosses the board's grain.
Ideally, the shim will contact the full thickness of the board, though in some cases, there will be slight gaps at the bottom. I usually cut clearance notches in the bottom of the shim so that I know it isn't bottoming out on the ribs, preventing full compression of the joint. This will allow the shim to protrude from the bottom, which though not esthetically pleasing, guarantees that I have full depth contact on the shim. Once again, done exactly right the shim will slide down into the crack, lubricated by the glue,until it is just flush with the bottom of the board. This requires flattening the bottom of the shim until it is as wide as the bottom of the routed "V".
Inre the sandpaper; after routing the crack, cutting the shim and rough fitting so that the shim is almost reaching the bottom, I use a piece of thin 220 aluminum oxide paper that almost as wide as the distance between ribs to mate the shim. I do this by threading the paper into the crack until I have an inch or so below the board to grip it with, lightly pressing the shim in on top of it, and slowly pulling the paper downwards so that it cuts the shim to mate with the board, effectively using the crack as a caul. I do this on both sides, all along the length. This doesn't cut the shim directly over the ribs, but those spots are easy to touch off with a small sanding block, or a horizontal pull of the paper with the shim in place. If this is done with the abrasive against the shim, it will leave a very slightly wider shim at the very top, since the thickness of the paper prevents the shim from seating all the way down and the paper doesn't cut into the very top, which will ultimately mate with the cracks edges. This very faint extra dimension, right at the top, makes for an invisible joint when the shim is pressed in with glue. The same effect can be had by using a 3-4 inch length of shim with the sandpaper pulled over it,abrasive out, and lightly sanding the crack to even out any router-chatter or aberrations. It helps if this shim/caul has a slightly sharper angle that the shim, itself. The slight discrepancy of angle between the resulting crack and shim, with glue, makes for an instantly tight joint when the shim is pressed in, hence my 'no clamp' method, (which started this whole digression).
That is the rough outline of my procedure, and let me say that "done exactly right" is not ALWAYS the result I get, just what I aim and hope for. If I can figure out how to do it, I will take pictures of a job I did 25 years ago that put 30' of shim in a Steinway A,(plus a panel under the bass bridge). The joints are still tight, and there are places I installed four or five short shims to repair a splintered section along the crack/separation).
I do little of this now, having, fortunately, developed a clientele that will pay for board replacements rather than just quieting the rattles of old, tired, compromised boards. I can still smell the spruce, though..
Regards,
