Making Scarf Joints
One of the unavoidable things we've all encountered in modeling, be it Kit or Scratch building, is the need for wood longer then what's commercially available. To get the added length we need, two sticks or sheets must be joined end-to-end. Well, we all know a butt joint is the absolute worst, so instead, a scarf joint is used.
A Scarf Joint is one where the wood is cut at an angle so that there's a greater glue surface joining the two segments. The rule of thumb for deciding on the angle is a 3:1 ratio. In other words, if you're joining 1/4" thick wood, the angle should span 3/4". An accurate fit in the joint is a must for a good strong bond, and getting the angle right is really easy using this method.
Once your joint is made, place it at a low stress area in the assembly. In wings, the closer to the tip the better, and it's always a good idea to stagger the joints so they're not aligned on the structure. And if you can place them where there's a sheer web or other such doublers, all the better.
Here's how it works..........
The size of the sticks to be joined doesn't matter, as long as they're the same.
The sticks are then laid together in preparation for sanding the angle.
Using a Disc Sander, the angle is sanded into both sticks at the same time.
As long as the angle is about a 3:1 ratio you'll be in good shape. The larger the glue surface of the joint, the better.
The angle is sanded and the sticks are ready to be joined.
Pin one stick to the board and lay a straight edge in place to insure the sticks are glued together nice and straight.
Glue the joint together using the straight edge as a guide. Any kind of glue will work nicely.
When dry, lift the wood from the board and block sand the joint smooth. If there are any small gaps, flood them with gap filling Cya and sand again before the glue dries. The sanding dust from the wood will wick into the wet glue and make a good solid filler and eliminate the gap.