Grain width for inlaid repair patches

[Wood Butcher]

It was my understanding, that when selecting new wood for an inlaid patch, that the grain should match as closely as possible to the original wood, and be jointed if necessary where it crosses the centre joint.

Sometimes I see sound post patches where the grain has been angled quite significantly, and the grain width bears no relation to the original wood. I understand that grains lined up perfectly could theoretically crack in the same place, but I'm not sure this actually happens. Other times I've seen chest patches, button grafts, back patches with very different spacing to the original wood.

My question is this: Can using very different grain width repair wood, or angling the grain, cause more problems down the line, rather than making things better as intended?
My feeling is that it will try to shrink differently, and may come apart or distort things in the years to come.

[Don Noon]

If a patch is visible, such as a button graft of new wood, then aesthetics is the main concern, and matching the wood is necessary.

For internal/unseen patches where only function matters, grain width matching should make no difference.  A slight angle to the grain could help prevent the development of new cracks, and if the angle is shallow einough (like in a bass bar), the differential expansion should be minimal.  For very large angles, there would be differential expansion as humidity changes (and differential shrinkage as glue joint dries and the wood ages)... but I couldn't say how much that would increase the likelihood of failure of the glue joint.  Sizing the parts before gluing I think would be a necessity, so as to minimize water-related expansion and subsequent shrinkage.

[jacobsaunders]

There was a school of thought where (for instance) a sound post patch should be turned a couple of annual rings clockwise, compared with the original belly wood. I strongly reject this theory. I remember repairing a cello that Austrian Airways had squashed on its way to Moscow which had been repaired like this. The result was a dreadfully complicated new sound post crack, jumping across annual rings, a bit like glueing shredded wheat together. If it had had a patch exactly aligned with the belly wood, it would have been a normal straight forward crack. One should resist the urge to “strengthen” violins/celli when repairing because it only means that it gets more comprehensively buggered next time it has an accident

[violguy]

Jacob,thanks for your thought provoking response to this problem.

[David Burgess]

On 9/5/2020 at 11:17 AM, jacobsaunders said:

There was a school of thought where (for instance) a sound post patch should be turned a couple of annual rings clockwise, compared with the original belly wood. I strongly reject this theory. I remember repairing a cello that Austrian Airways had squashed on its way to Moscow which had been repaired like this. The result was a dreadfully complicated new sound post crack, jumping across annual rings, a bit like glueing shredded wheat together. If it had had a patch exactly aligned with the belly wood, it would have been a normal straight forward crack.

I agree.

[HoGo]

On 9/5/2020 at 5:17 PM, jacobsaunders said:

There was a school of thought where (for instance) a sound post patch should be turned a couple of annual rings clockwise, compared with the original belly wood. I strongly reject this theory. I remember repairing a cello that Austrian Airways had squashed on its way to Moscow which had been repaired like this. The result was a dreadfully complicated new sound post crack, jumping across annual rings, a bit like glueing shredded wheat together. If it had had a patch exactly aligned with the belly wood, it would have been a normal straight forward crack. One should resist the urge to “strengthen” violins/celli when repairing because it only means that it gets more comprehensively buggered next time it has an accident

Agree totally, that was my first thought after reading OP. It may be sounding as marginally stronger repair but in the case that Jacob describes it becomes a nightmare. In world of mandolins we often see similar problems with mandolins that have f hole areas reinforced with fabric (often soaked with Titebond as recommended by many builders to strengthen this vulnerable area...). Repairing and cleating simple f hole crack becomes PITA (mandolins are not generally opened unless the damage is really bad and all work is done through f-holes).

[Jeffrey Holmes]

On 9/5/2020 at 11:17 AM, jacobsaunders said:

There was a school of thought where (for instance) a sound post patch should be turned a couple of annual rings clockwise, compared with the original belly wood. I strongly reject this theory. I remember repairing a cello that Austrian Airways had squashed on its way to Moscow which had been repaired like this. The result was a dreadfully complicated new sound post crack, jumping across annual rings, a bit like glueing shredded wheat together. If it had had a patch exactly aligned with the belly wood, it would have been a normal straight forward crack. One should resist the urge to “strengthen” violins/celli when repairing because it only means that it gets more comprehensively buggered next time it has an accident

I also agree.

 

[Wood Butcher]

Thank you all for the replies so far. 
It would seem that the grain width matching, is far less of an issue than the grain following the original direction precisely.