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Best way to repair a new, pressurised saddle crack?


bean_fidhleir

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My fiddle has a new saddle crack that's a bit bowed up from the surface, as though the saddle is being pulled toward the neck and is compressing the table such that it has to bow to get relief.

What's the best way to repair it?

My first thought is to make up some water-thin glue, drizzle it into the crack with a hypo, then slack the strings to relieve the bowing, let the glue set up (possibly with a bit of a weight or clamp to keep the edges of the crack well-mated, and finally trim a sukoshi off either the saddle or the table where it meets the saddle so that, when I reapply tension to the strings, the same compression doesn't recur.

Thoughts?

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First, take off the strings, bridge and tailpiece. When gluing a top crack from the outside, I always separate the top/rib seam to allow the crack to close as much as possible and to allow flexing of the crack to work in the glue. For a saddle crack I separate the seam from the crack at least to the nearest lower corner. I use a strap-type crack clamp to pull the crack together. Although this type of clamp is not always terribly effective for cracks at the ends of the plates, you can't use any other type of clamp without removing the plate.

Down pressure on the crack can often be exerted by inserting a wood wedge under the bar of the clamp, but make sure to put a piece of waxed paper under the wedge so it doesn't get glued to the top. Again, the wedge often not terribly effective for cracks at the ends of the plates, in which case I find myself improvising any type of clamp that will span the body, bearing on the top and the back. (Don't forget the waxed paper.) I also like to put a top-gluing clamp on each side of the crack clamp where the top is unglued from the rib to prevent the top from curling away from the rib under the force of the crack clamp.

After the clamping system is ready, I warm the crack area under my work lamp while the glue is heating. When the glue is warm, I brush it along the crack. With one hand I brush the glue while I flex the crack with the other hand for about 15 seconds or until I'm sure that the glue has fully penetrated the crack. I wipe off the excess glue, put on the top-gluing clamps, the crack clamp, the waxed paper and the downward pressing wedge or clamp.

After a few hours, or overnight, I remove the clamps, wash off any glue residue and reglue the open top/rib seam. When that glue is dry, the instrument can be set up again.

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My fiddle has a new saddle crack that's a bit bowed up from the surface, as though the saddle is being pulled toward the neck and is compressing the table such that it has to bow to get relief.

What's the best way to repair it?

My first thought is to make up some water-thin glue, drizzle it into the crack with a hypo, then slack the strings to relieve the bowing, let the glue set up (possibly with a bit of a weight or clamp to keep the edges of the crack well-mated, and finally trim a sukoshi off either the saddle or the table where it meets the saddle so that, when I reapply tension to the strings, the same compression doesn't recur.

Thoughts?

Think you may have two things going on here...

A correctly shaped saddle should transfer very little pressure to the top... This is something you'll probably need to address.

Now, the saddle crack itself... I may not be understanding the situation entirely (no photo)... but:

If it was caused by the top shrinking down against the saddle, it's currently under tension (the crack is being held open). If the crack isn't too far out of register, and you carefully separate the block area from the top leaving the saddle in, you may be able to do the following:

Work glue into the crack. Remove the saddle (which, will allow the crack to snap closed. Brad's wax paper for isolation is a good idea at this stage. Register the crack. Pull the wax paper. Glue the block area back down (which can also help keep the crack in register). Let every dry. Burnish the crack (lightly) if needed. Fill & touch up if needed. Reshape the saddle (so it doesn't push against the top any longer). Relieve the saddle (so that it's no longer tight against the sides). Glue the saddle in place.

Good luck!

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Thanks, both. It's a scary situation, but I'll do my best.

A few more questions:

What thickness should the glue be? Can I melt it in a jar sitting in boiling(?) water, and thin it with...tap? distilled? something else?

What's the best way to separate the block/table and rib/table joins? Palette knife and...anything? hot water? alcohol? something else?

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"What thickness should the glue be?"

For this purpose, I make it on the thin side so I will penetrate the crack easier.

"Can I melt it in a jar sitting in boiling(?) water, and thin it with...tap? distilled? something else?"

The dry glue is mixed with water and left to absorb the water for about an hour before heating. I use tap water. I use a jar in a water bath, but the water shouldn't go above about 150 degrees F. A cover on the jar is helpful to slow down water evaporation from the glue. After the heat liquifies the glue, more water can be added to adjust the thickness of the glue.

"What's the best way to separate the block/table and rib/table joins? Palette knife and...anything? hot water? alcohol? something else?"

I use a thin blade similar to a pallette knife -- no water or alcohol. Sometimes seams open easily and sometimes not. It can be tricky if it is glued too solidly. It must be done carefully to avoid damaging the underside of the top edge or even creating new cracks.

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