Author: jasperbay
Date: 2010-04-22 17:47
Just finished bringing a nice Leblanc Alto 'back from the dead' by repairing several cracks in the throat area, the most common 'crack zone', and thought I'd jot down a few tips for DIY'ers.
Crack repair of wood clarinets nowadays is done almost exclusively with thin CA (cyano-acrylic superglue) strengthened with grenadilla 'sanding dust'. This glue (I get it from model-airplane hobbiist suppliers on E-bay, usually in the 2oz. size for @$10) adhers to the very oily/waxy grenadilla wood much better than epoxy, and can be sanded down with a popsicle stick with glued on sandpaper to a near-invisable repair. Often, a 'hairline' crack need not be "pinned", just CA glued with sanding dust added for strength and color match.
Using thin CA glue (I see little use for medium or thick 'gap-filling CA glue) can be a real pain-in -the-rear, since it has the consistency of water, but thats how it 'wicks' deep into the crack and does such a great job! CA glue suppliers often include tiny disposable application nozzles, sometimes these work, sometimes not. I use a technique that takes all the 'fear factor' out of applying superglue: First, drill a couple 1/4" holes in a block of lead (or plastic, steel, aluminum, your choice) with a 1/4" drill. This is your CA glue 'inkwell'. Put in a couple drops of glue, it won't harden for 10-15minutes. Your CA glue 'pen' is a large toothpick, or similar, sharpened to a 'chisel' tip. This you dip into the CA 'inkwell', it will hold something like a tenth of a 'drop', and allow you to place the glue safely and with precision exactly where you want it! As the glue 'wicks' into the crack, you will have to keep adding 'dabs' of glue, usually untill the crack won't take any more, and the glue starts to set. Sprinkle grenadilla sanding dust into the crack as you add more glue. (black walnut dust will work in a pinch, or ebony).
If the crack is seriously large, or may be subject to movement, you may want to "pin" the crack, with short pieces of threaded steel, available from Ferree's Tools. This will help stabilize the crack, and with CA glue should make a strong repair. I'm keeping my fingers crossed, have'nt had one open up again yet.
I like to 'degrease' the crack with MEK or laquer thinner, applied with a small brush, and blown out with compressed air. I believe this makes the repair a little stronger, but will remove any black stain sometimes present, and require more work later during final sanding/buffing/oiling. Also, its best to never sand with your fingertips, always use a flat sanding device like a popsicle stick with different grits of sandpaper (wet-or-dry automotive type works well) to avoid subtle dips, humps, etc. that result from fingertip sanding.
CA glue also works well for tightening loose posts, building up chipped tenons, filling in the holes drilled for "pinning", repairing mouthpieces, etc., etc. Go forth and repair!!
Clark G. Sherwood
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