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Johns Web Site
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Date: 7-13-2015
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Number of Hours: 2.50
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Manual Reference:
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Brief Description: Updrilling and Prepping the Bottom Surface
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With the fuselage on its side, 327 rivet holes were upsized to #30.
The center of the step opening in the bottom skin had been drilled to ½” using a ¾” wood dowel as a drill bushing in the step mount tube. See the May 31, 2015 log entry. Today, a ¾” spade drill was inserted stem first through the step mount tube and through the previously drilled hole in the bottom skin. The stem was then chucked in a hand drill from the outside, and slowly turned to clear the excess powder coat from the step mount tube I.D. By working from the back side of the spade drill, the sharp tips of the drill will not gouge the I.D. of the tube.
A new, sharp, ¾” hole saw was slightly modified by grinding the outside diameter of the teeth by mounting it on a ¼” steel tube, then spinning it by hand against a grinding wheel so the teeth would not cut on the O.D. The hole saw, still mounted on the ¼” steel tube, and clamped in the hand drill, was then inserted through the step mount tube from inside the fuselage. With the drill turning slowly, and with very light pressure, the hole in the bottom skin was easily cut exactly concentric with the opening in the step tube mount. A little WD-40 on the outside of the hole saw makes it ride easier through the tube. A minor amount of deburring, and it will be a perfect fit to the step.
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Cleaning the Excess Powder Coat Form the I.D. of the Mounting Tube
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Hole Saw Breaking Through the Bottom Skin
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Finished Hole Ready for Deburring
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