Thursday, September 13, 2007

Broken Sticks

Since I am in a sense running a grand experiment in that I am using PU instead of epoxy for any joints where I have smooth flat surfaces to join, I thought a break test would be in order.

I found two oak offcuts about 12" long, 1" thick, and sloped to a point and glues them up as a scarf joint. Albeit a short scarf joint at about 6" long. PU was applied and they were heavily clamped and left for 24 hours.

Where I have laminated peices with PU, any cuts that have crossed the join have shown a what could be a single peice of wood except for the grain. So I was expecting great things.

The scarfed oak stick took my 200+ lbs quite happily, until I started to bounce up and down.

Then it broke approximately along the line of the scarf, The glue did not fail, rather the wood broke apart. If you look at the two peices of wood, each has hills and hollows where it either tore wood from the other side or wood was torn from it.

In one or two tiny patches the break was along the glue line, but mostly the wood actually failed.

I appreciate that the scarf was short at nearer 5 to 1 than 8 to one, so my next test peice will be 8 to 1 and will be better prepared - this was really two bits of scrap thrown together.

But I was sort of hoping for the wood to break like a single peice or wood. I'll try to post a picture later.

And I'll post the results of a proper 1:8 scarf subject to the bounce test.

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