Hatz Biplane Association

I find that while there are quite a few websites you can go to to find good photos of how to make the ribs for example, other tasks are a bit of a mystery - at least for a noob like myself.
I therefore decided that when I figure something out, I'll share it.
Here is how I manufactured the hinges for the elevators and rudder (the trim tab is a smaller version of these, but the rest are identical as far as I can tell).

Step one: Have the strip that wraps around the short tube section that becomes the hinge and the hinge tube section cut to size. Better leave the strip a bit longer at this stage. Mark the center of the strip: Step two: We need to find the place for drilling the other two holes in the strip for the rosette weld. I placed the tube near a 90° corner, and then rotated the strip from center-over-tube, 90° to one side. This gave me the location for a hole (repeat for other side): Step three: With the holes drilled on the marks, place the strip perpendicular to a 3/4 tube we will use as a bending radius. In hindsight something slightly larger would have been better, perhaps 13/16", because the strip will be actually welded to a 7/8" short piece of tubing. The angle piece is used to find the perpendicularity between the tube and the strip.
(continued in part 2)

Step four: Now a little elbow grease is applied: Step five: Due to the spring back, finish the bend in the vise: The result: Next, the rosette weld.
Still haven't figure that one out yet... What size holes did others use?

AC43-13 has a bunch of good information on how to determine the size of the rosettes and how to deal with various repairs involving splices, finger patches, sleeves, etc...

The rosette answer is in section 4-84 on page 4-56 (page 201 of the .pdf document)
It reads:
"4-84.
ROSETTE WELDS
are generally employed to fuse an inner reinforcing tube (liner) with the outer member. Where a rosette
weld is used, drill a hole, (in the outside tube only) of sufficient size to insure fusion of the inner tube.
A hole diameter of approximately one-fourth the tube diameter of the outer tube serves adequately for
this purpose. In cases of tight-fitting sleeves or inner liners, the rosettes may be omitted. Rosette weld
edge distance is 1/2 the diameter of the tube, as measured from the edge of the rosette hole to the end of the
inside and outside tube. Rosettes shall not be considered when determining the strength of a welded form.
Drill an 1/8-inch hole in the lower tube in the center of the intended rosette weld so the heat does not burn
away the outer tube. This small hole tends to bleed off the heat from the torch and keeps the size of the rosette
small."

The other info can be found in section 4-91 starting on page 4-62 (page 207 of the .pdf document)

http://www.faa.gov/documentLibrary/medi ... .13-1B.pdf

Thanks Doug,
I guess I just need more practice. My rosette welds are not coming out well. I plug the hole nicely, but the weld to the inner tube is weak, as it does not pass the hammer test. My guess is I need to focus the heat more on the inner tube.
Thanks again.

Here's a question to the group:
With this hinge design, metal-on-metal, how do you lubricate the hinge? Just a drop of oil in the very small gap between the moving tube and the two rings on each side, which are welded to the leading edge?

One drop of oil on each side of the hinge once a year has worked out well for me.
In making the hinge, I formed the strap and drilled 1/8 inch holes through both pieces and then opened up the holes in the strap to 3/16 inch. From there it was easy to form the rosette weld because there was no heat blow back and both parts would start to melt at the same time. Then you just buff up the inside of the bearing surface until it is smooth.
John Hanson