Tuesday, October 30, 2012

Upper Rudder Hinge

These pictures are of the lower hinge.  It is made the same as the upper hinge but it is on the 1 1/4" tail post which the fin rear spar (1 1/8") fits into.  It's made form 16 gauge (.o5o") steel 1" wide.  The 1" wide strap which goes around the rudder spar is made from 18 ga. (.040") steel.  It bolts to the hole through the tail post and hinge.  That hole has a bushing in the tail post.  The bolt hole in the hinge is larger than the bushing O.D. which allows the 3 pieces to be welded together, with the weld below the surface of the hinge.  This lets the strap bolt on nicely.
The ends of the hinge are formed to fit the tail post and welded on all the way around.  The bottom of the hinge socket has a dimple running the full width.  It appears to have 2 advantages.  It provides a nice place to weld the hinge to the post without the weld being in the bearing area.  It also adds some gap between the rudder and fin to allow more room for the fabric covering, surface tapes, and dope.  I've never seen the hinges on a real stabilizer so it makes me wonder if they were really made in the same way.  The WACO TEN hinge drawing doesn't have this feature.

I started with a strip of steel about 7" long.  The first step was to put the dimple into center of the strip.  The vise was adjusted to have about 1/4" gap.  You can't see it here but there is a slight radius filed on the jaws and then steel jaw covers add a little more.  A 3/16" drill was pounded into the strip to form the dimple.  The strip is bent a little but the shape is perfect to start forming the socket shape.  The drill was pounded in to about 3/4 of it's diameter.

To clamp the part for forming and keep the dimple from flattening, I made a support block from a bar of 1/4" steel.  A 1/4" slot was cut 1 1/14" into the steel and the edges rounded to fit the hinge.  With the bar clamped in the vise, the hinge was clamped to it with a 3/4" socket to use as a form tool.  The ends of the hinge were bent around the socket as far as possible making a "U" shaped part.

The hinge with the socket and bar still clamped to it was held in the vise so the ends of the hinge could be bent 90 degrees to the socket.  OK, I was having fun and forgot to take a picture.  With the side "U" bends started it was stood back up in the vise and the sheet metal pliers used to bend the ends 180 degrees.  These bends were tightened a little with a clamp.  With the clamp still in place the ends were bent back to be 1-1/8" apart and close to parallel.  The bends to do this were made about even with the dimple.

To locate the bolt holes the ends of the hinge were squared to the fin in the jig.  The holes were then drilled based on this dimension from the formed ends.  I drilled the holes 7/16" dia. to give clearance for welding.

I used a slightly larger (22mm) socket to hammer the ends to fit around the spar.

The finished part fits great.  Now I just need the remains of hurricane Sandy to pass so I can use my outdoor welding booth.

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