Monday, January 2, 2012

Biscuit Joint on High Chair Seat

I showed you all pictures of this high chair when it was in 18 pieces, a few posts back.  Well, we are moving forward with the project and are to the point where we need to put the seat back together.  The high chair is made of maple, and the seat is pieced together. The combination of those to factors caused a very common problem.  Maple very frequently looses moisture over time which causes it to shrink.  When the wood shrinks, the joints separate and the seat falls apart.  In addition to the shrinkage problem,  the way these type of seats used to be put together was with a 'butt joint'.  Meaning that it was two flat pieces of wood stuck together with glue.  This isn't a particularly strong type of adhesion method!
To fix the problems with this seat we started out by cleaning any old glue off of the pieces of the seat so that we have a clean work surface.  If this step is skipped, then any new glue could just adhere to the old glue, not to the wood, and the joints would fail again.  We then used what is called a 'Biscuit Joint' to secure the pieces together.  Small grooves were cut in the wood using a 'biscuit jointer'.  This is an exacting job, as the grooves need to be perfectly aligned. A thin oval shaped piece of wood called a 'biscuit' is then glued into one set of grooves.  Once the glue is dry, the same biscuit, attached now to a piece of wood, is glued into the matching set of grooves on the other piece of wood.  This process, if done well, leaves a very tight, sturdy joint that is completely invisible.

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