Replacing Old Door Skins
from Custom Planes, September 1999
Once upon a time there was an old Stinson Voyager undergoing a very nice restoration, and so its decrepit old
cockpit doors needed an overhaul. This is the story of one way to do it.
Because the door frames (6061) showed signs of old repairs, and because the skins needed replacement, the
simplest approach was to separate the skins from the frames. First, I needed to find all the spot welds,
(highlighting them by sanding helped), and then, I needed to break the welds carefully. Because the
frames were a thicker section (.032 inch) than the skins (.025 inch), they came apart quickly, leaving
most of the weld nuggets standing proud on the frames.
I then removed the old patches from the frames and cleaned and tack-welded the numerous cracks.
Next, I jigged up the now-flabby frames to match the fuselage with a simple set of wood blocks, finished the
welding and dressed off the welds. The cleaned-up frames then fit into the opening and also matched the
outer fuselage contour.
Realigning the old skins to the jigged frames and then checking the surface with a straightedge confirmed the
compound nature of the skin surfaces. Closer analysis revealed exactly where the crown centered, the
height of it and the rate of rise. Thinking over the choices of handwork, air hammer or wheel, I decided
on the wheel because of the skin thickness. A few passes with light pressure had it close, and another
few centered up the crown quite nicely.
Fastening them back together had already been thought through while doing the prior drudge work: Because
there is thick foam weather strip all around the inside door edge, I would double-dimple and flush-set
the AN426 A3-4 AD rivets on a 1:1 replacement for the spot-welds. Using the lattice-spacer and the handy
homemade universal dimpler made short work of the riveting task. I used a 4AX gun (very light) to dimple,
using a rivet for the male die, and to set the rivets, as well. (I advise practicing for a while on scrap
for this trick, because tool line-up is really important.)
When everything was completely fastened, I went over the completed doors with the finishing spoon and
small shot bag
to tune up the contours for paint. A touch with the sander helped with a few burrs, and according to the
owner, they now fit better than new.
A thorough inspection of both doors revealed damage to both the skins and the frames, with patches and
doublers hiding cracks and broken welds. However, the door shapes seemed sort of consistent with both
the door openings and the contour of the fuselage. The doublers were removed first, as they were
preventing the frames from curving properly.
Measurement of the metal thickness revealed .025" skins and .032" frames spot-welded together. The alloy is
6061 and the temper is T3, as seen from the markings still left. Sanding the skin lightly reveals
location, number, and diameter of spot welds. A nick with the rotary file (burr) insures that the chisel
will break the weld cleanly, leaving the nugget on the frame.