Bear Meadow
'Laparoscopic' Crack Repair Techniques

Repairing stringed musical instruments when there is no manual (sometimes not even visual) access to the interior has always been a challenge. The techniques described and illustrated here will enable an accomplished luthier or repair person to reliably repair top cracks and install cross-cleat reinforcement without access to the interior except through the soundhole, with complete confidence in the integrity of the work.

The first step in the process is clamping and closing the crack itself. Pairs of super magnets have been used for some time now for these situations, enabling the edges of the crack to be accurately aligned with each other. What has been missing is a way to guarantee that the inner magnet will not be captured by stray glue inside the instrument, beyond reach and retrieval. The Bear Meadow contribution of this is a Teflon cap, machined to very thin walls (.020" thick), which is a slip fit on standard 9/16"x3/16" magnets. The use of this cap as a shield between the inner magnet guarantees that the magnet (nor the cap!) gets glued in place, regardless of any glue used.

To get the crack edges aligned and clamped, pairs of these magnets are applied along the crack. First the outer surface of the crack is lined with waxed paper, to make sure the surface is not marred by the magnet or any dust picked up by the Teflon cap. The inner magnet is slipped through the soundhole, and captured by a mating capped magnet, and guided to its place along the crack. Depending on the nature and extent of the crack, magnets may be placed about 4 inches away from each other as needed to fully align the to edges of the crack. Light quick-acting clamps can now be applied laterally to the crack as necessary to complete closure.

Once the magnets are stationed and all decisions have been made about staging lateral clamps and magnet clamps, the lateral clamps can be removed and stationed nearby, and magnets moved to one side of the crack and the wax paper lifted and pinned or clamped to allow free movement of the crack while inserting the repair glue. For casual work, cyano-acrylate glue (CA, 'crazy glue,' etc.). For curatorial purposes or work on legacy heritage instruments, liquid fish glue ('LFG') is recommended. The drawback of LFG is also its virtue: it has an 'open time' of about half an hour, but requires clamping for 12 hours for the glue to completely set.

When the joint glue has set, slide the magnets toward the soundhole for withdrawal of the interior magnet. Clean up and refinish the surface as needed. The next step is to install interior reinforcing cleats!