[Jim Nunn]

The most common fit issue I see is on tubes, and the fit of the skin over the forming bulkheads on ship hulls and aircraft fuselage. As a rule cut the forming bulkheads on the inside of the line and the skins on the outside of the line. In most cases you will need to sand the forming bulkheads to get the best fit.

Why this is so is that most us builders do not take into consideration the thickness of the paper. Lets say we are making a 0.200 in tube with a round inside former. The designer uses the circumference of the former as the dimension for the skin. In this example .200 * 3.1415 = .628 inch. In reality the length should be .200 + (2* the thickness of the paper skin) * 3.1415. The thickness of 67 lb paper will range from .0075 to .009 inch. Using the 0.009 dimension the length should be 0.684 so you would end up with a .056 gap. This is of course the worst case example most designers do take into consideration the thickness of the paper, but even a small difference in the paper thickness will make a difference and create seam issues. Note this error is constant it does not vary with the diameter of the inside former.

Back to the beginning check the fit, recheck the fit and its better to under size on bulkhead formers.

Start building simple models too get the “feel’ of working with paper. There are several good models in our down load section and of course there are free models on the net.

Jim Nunn