Brief Description: Step 4 of Rib Building - glue test blocks
One of the concerns we have when building a wooden airplane component with glue is whether the glue has the required strength. We can either take it on faith or test it. Guess which I do?
Epoxy is a two-part glue that has a very long shelf life before the two parts of the glue are mixed together. Once mixed, they have a finite life.... working life or pot life. That's how long you have until you better have all your bits together.
In addition to time constraints imposed by the ongoing chemical reactions of the two parts of the glue, there is the question of how well the glue was prepared... was the mix ratio (the ratio of the volume of weight of one part to the second part) correct? Was the mixing bowl contaminated? Etc.
It's a good practice to make test blocks for each batch of glue you mix up to build the plane. I use pine wood (locally available, cheap, and has similar porosity to spruce) for my test blocks. They are 1 inch square and about 3/4 inch thick. I use the glue fromt he end of the batch, put some on the surfaces of the test blocks, and treat it as I would the final airplane part. It gets numbered and annotated so I know what it was for. A week later, I put it in a vice and test it to failiure. The glue joint should remain intact and the wood should break.
Success! The wooden blocks broke right where they were supposed to. And the glue joint remained intact.
Assembled test block.
Test blocks ready to test to their breaking point.