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How does wood grain affect the strength of dowels?

Shop for Dowels

Image showing a corner joint reinforced with dowels Dowels are used to strengthen joints between two pieces of wood. Irrespective of the direction in which the joint has been made, the two pieces of wood will always be creating tension on the dowel.
Image showing how pressure affects dowel pins on horizontal wood joints This means that when pressure is applied to the surface of either piece of wood, they push down on either end of the dowel, almost as if they are trying to bend it.
Image to show how wood can split along the grain Wood is prone to splitting along the grain, so making dowels with grain that runs along their length prevents potential splitting, as tension is only created on horizontal joints (against the grain).
Image of wood with compact straight grain which is ideal for making dowel pins The straighter and more compact the grain, the stronger the dowel will be.
Wonkee Donkee encourages the DIYer to think of the grain in a dowel as reinforcing struts