Monday 2 May 2011

Making wood do un-natural things

I knew at some point soon, I would need a set of lower wing tip bows, as these set the final spar lengths, so I took a break from metal fittings to build the two lower wing bows.

I started by ripping 14 strips of spruce, 2 inch by 1/8th" by 7 feet.
I wanted the finish bow width to be 1" which would match the leading edge spar, and also matched the amount I had left off the ribs to the leading edge point.
So 7 strips inclusive of the glue would make up 1" in width.

I next needed a fixture to laminate the bows, and I knew from experience you cannot have enough clamps or clamping points when making a bow.
Shown above is the jig blocks screwed in place, around the wing tip bow shape. I made a template of the EAA replica lower wing tip, and then matched this to my pre measured spar locations, so I knew all would (should) match up.

Also shown are the spruce strips. They have already been soaked in a bathtub of boiling water with ammonia added.
(ammonia softens the fibers of the wood and allows it to easily be clamped in place)
The thoroughly soaked strips are then clamped onto the bow fixture with NO glue and allowed to dry.
Once they dry the clamps are removed and the various strips will have taken on the required final shape.
Next glue is applied to all the strips, and they are re assembled and clamped in place. The more glue wiped away when wet will make the final clean up much easier. Care must be taken to not glue the strips to the fixture!
and the finished laminated wing tip bow. Once the bow is dry, it is removed from the fixture and cleaned up by running it through the table saw. The LH and RH bows are the same at this point, as they still will need to be cut down and trimmed to final shape, then tapered and rounded.
and with the wing tip bow shapes determined, the spars can then be trimmed and tapered to final shape.

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