Sequoia Aircraft Corporation F.8L Falco, Construction Manual

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F.8L Falco Construction Manual 10–5 Revision 4, March 1, 2002
will be 12mm wide. Measure off the 12mm dimension and draw a line. The scarf can then be
sanded to this line. If you are very careful and skillful, you can do most of the scarf with a power
sander. You should finish off the scarf with a sanding block or Disston abrader.
correct
too much overlap
incorrect
Figure 6
In gluing a scarf joint, one of the most important considerations is to prevent end slippage. An
effort should be made to keep the parts in proper alignment as illustrated in Figure 6. A small
amount of overlap as illustrated is desirable and insures that the joint will receive adequate
pressure. If the members slip excessively endwise during the clamping operation, a condition will
occur (illustrated as “incorrect”) in which the members will not receive sufficient and uniform
pressure and erratic joint strength may be expected. The condition of too much overlap is to be
preferred to insufficient overlap, however it is possible that the scarf joint will receive higher
pressure than intended and some crushing may result, but it is probably that the quality of the glue
joint will not be adversely affected. It is important to provide some method, such as blocking or
clamping the ends of the members, to prevent end slippage. Blocking or clamping should also be
arranged to minimize side slippage and thus prevent unnecessary waste of material. Wood pins of
small diameter driven into drilled holes are sometimes used to prevent end and side slippage.
These pins have an advantage over nails, sometimes used for the same purpose, in that they can
be left in and do not interfere with subsequent machining operations.
Conditioning
With the exception of epoxy glues, cold gluing operations add moisture to the wood in varying
percentages. Glue that has set in joints contains only a part of the water added at the time of
mixing, the remainder having been absorbed by the wood or removed by evaporation. The
absorbed moisture must be allowed to dry out or to distribute itself through the wood in order to
insure the full strength of the joint and to reduce the tendency of the glued member to warp.
In gluing thick laminations, the moisture from the glue need not be eliminated but may simply be
allowed to distribute itself throughout the construction. Complete equalization would require a
very long time. For woods that permit a rapid distribution of moisture, such as spruce, a 3- to 5-
day period should suffice under most conditions. When heavy constructions are glued from
laminations one-eighth inch or less in thickness, however, they will normally contain too much
moisture after gluing and should be dried for 1 to 3 weeks or longer, depending on their thickness
and width and the conditions of drying.