Jim
Dalens Rib Jig
Jim Dalen,
a RagWing Parasol builder sent us a copy of an article he wrote
for his local UL club (the Albuquerque Ultralight Association) newsletter.
Constructing the wing ribs is still the primary focus in my garage
and I've taken some photos of the jig and the assembly process that
might assist another builder. I made the jig from an old section
of preformed countertop. After trimming the excess material, I ended
up with a flat section that is about 16" X 50". Nailing
and gluing a 1.5" strip along a factory straight edge at the
"wrong side" provided a perfect 90 degree and straight
corner from which to construct the ribs. A full size rib pattern
was then attached to the particle board with wall paper paste after
all key measurements were verified on the pattern. I started to
construct a cam arrangement for alignment during the rib construction,
but found that 8d finishing nails placed into predrilled 7/64"
holes held the pieces firmly and uniformly in place for gluing.
This jig uses 22 of these "pegs". The proper placement
of the holes was determined by actual placement and bending of the
wood strips. "See photo # 1). The rib is assembled in the jig
by 1st placing the lower and upper stock in place, fitting and gluing
the trailing edge joint and then fitting, cutting and gluing the
remaining stock pieces. The plans of the Parasol call for the joints
in the ribs to just be left at a 90 degree cut and to rely on the
gussets to support the stress at the joints. I am not comfortable
with the resulting gaps so all of the joints are fit and cut to
the proper angel by simply laying the stock over the existing upper
and lower stock at the correct angle as determined by the plans,
marking the correct dimension and angle with a fine lead mechanical
pencil and cutting with a hacksaw. (Photo #2 shows the fine fit
possible by using this technique and also illustrated the positing
of the stock by use of the finishing nail pegs.)
After all the stock is glued, the gussets are cut and glued in
place. I am using the EXCEL glue recommended by Rag Wing and find
that it expands as it dries. The plans for the craft call for use
of staples to secure the gussets until they are dry but I use wood
clothes pins to clamp each gusset in one or two places. Half of
the clothes pin was shorted to just less than the spring slot and
then permanently screwed in place. After the gusset is cut and glue
applied, the top half is simply slipped under the center spring
and then acts as a clamp while the glue dries. (See photo #3 and
compare the clamps to photo #2.)
This jig setup works well for me and the only problem encountered
was another case of pilot error when I didn't get the waxed paper
positioned correctly and glued a peg to the wood stock! That little
error proved the exceptional adhesive qualities of EXCEL glue.
