A Record of important things…

Finished Vertical Fin

Finished construction on vertical fin.  Primed the inside of the spar and the fin sections by just cleaning and pouring in the primer and sloshing it around.  Should be good enough since the fins are already alclad.  The outsides are primed too.  I am a prime-as-you-go kind of guy having had bad experiences with corrosion in the past.

Here’s  little trick I read about elsewhere and modified a bit.  To locate the exact, precise centerline of the steel spar under the fin I got these little powerful half inch round neodymium magnets.  They naturally seek the spar centerline.  Just prior to the rivet location, make a little “puddle” of  Sharpie ink (or machinist's ink if you have it) and “push” the magnet through the puddle across the rivet line using a piece of aluminum. 

Invariably the spar is not precisely on the measured and marked centerline.  Using this trick the magnet pushes a line of ink and gives you the exact drill point.  This one is toward the end of the fin and is off the measured line by about 1/16th of an inch. 

Had I just drilled on the drawn spar line the rivet would have been slightly off center of the spar  and a dimple would have resulted when the rivet drew things together and canted .

Here are the pieces coming together for the final time before riveting.  You can see where I drilled out the lower rivets of the lower section so the curved tube would fit through without damaging the thin skin.