Wisdom vs courage

Results are in from my scarf joint test. I released the clamp after 24 hours cure time, and this is what I found:

Side-A looked fairly good. This is the side facing up; the side I could see when I mated the two scarf surfaces.

  

  

Side-B was a mis-matched disaster. This side of the joint is beyond ugly. No amount of sanding and filling would fix this mess.

Thus, this first test revealed at least two seam fitting failures:

• The faces of the test scarfs were imprecisely cut. I have to devise a way to scarf with much finer tolerances; to make cuts of near equal slope and width; and,

• The two pieces being joined were glued together cockeyed on the bottom side of the joint. I will have to figure out a way to index the two pieces together so I can be sure the bottom side of the joint is as well aligned as the side I can see.

And what about strength?

This is one strong puppy. I jumped up and down on it and it did not break.

 

  One big problem, though: It would not bend. This is not good, because the finished top must have a nice pleasing curvature along the same axis as its scarffed seams.

It is decision time. Press on courageously to the full-size marine plywood panels and hope the joints work out better this time? Or, stand back, analyze and test another method?

I am taking the latter course.

And then there’s the inflexibility problem. This is serious. The final seams will have be bendable. The finished top must have a gentle arch.

I think greater seam flexibility will come from cleaner cuts and thinner glue. In the next test, I will use a soupy glue mix instead of the peanut butter consistency stuff I slathered on the first time.

So, as much as I would like to charge ahead, it’s back to the test bench. I think it is better to grope around for the right joining technique using inexpensive materials, than to try and fix botched joints in the real stuff.

Lessons learned: Better mating cuts. Thinner glue. More patience.