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Shrinkage and Struts

   The results of shrinkage will ofetn be seen in the strutting and linings. In the following cases the struts will need shortening.
 

     Here we can see evidence that shows lateral shrinkage IS more than longitudinal. On this de Meglio, the tulipwood edging has been pushed off where the struts meet the tulipwood edge.     On the opposite side it was the same. The struts have shrunk lengthways (longitudinal grain) much less than the top has shrunk laterally (across the grain).      In extreme cases, this shrinkage difference will force the purfling, glued to the side, away from the rest of the top. The integrity of the top is now compromised and buckling often follows, as here.

    This is a view of the underside of the top. In this drastic example, the struts remained in place, while the purfling, and the top shrank inwards away from the edges leaving a very visible gap.

 Another example of the same thing. This can often happen on both sides of the instrument, because the edging is securely glued, the centre-join re-enforced, leaving the thinnest part of the top, under the purfling, to split. In this example, the struts were all in place, and there was no splitting of the top, but it moved nevertheless. Once removed, the cause was found to be a broken strut end, where it can be quite thin.

 

Linings

Linings are thin strips of wood glued at the top and inside the sides to strengthen the structure, provide a seating for the struts, and a slightly wider surface on which to glue the top. They are very important to the integrity of the structure. Some cheap mandolins, produced quickly and cheaply for the mass market, will be found without these linings, and often have detached tops.
  In this instance, linings do not reach all the way round. They are either side for the struts, but not round the tail. Mandolins like this, often split around the seam of the top/side join.      In this much better quality de Meglio, the lining reaches all the way round. Splits around the bottom edges are much less common.      In this example, when the crumpled top was removed, the cause became clear. The strut slots in the linings were much too deep, so not supporting the ends of the struts well.
      
On this instrument, there are no linings around the sides at this point, and shrinkage has forced the top and the edging apart where the top is thinnest, under the purfling.      Here it is possible to see that the strut top is not level with the lining top at all. This must have supported the top very badly.