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Johns Web Site
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Date: 1-2-2015
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Number of Hours: 0.00
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Manual Reference:
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Brief Description: Spar Drilling tooling
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The spars are arguably the most critical assembly in any normally configured aircraft. They carry loads between the wings and fuselage; so the accuracy and repeatability of the assembly processes are very important. To couple the loads among the spar components, the rivets and bolts must be correctly applied, and this requires precision holes, especially for the bolts. The rivets require slightly less precision, because the rivets swell somewhat to fit the hole diameter when they are set.
After reviewing the potential processes that would: insure the holes are perpendicular to the spar web, keep the holes straight (not subject to manual wavering,) and keep the assembly tightly clamped while drilling or reaming, I decided to use a precision clamped drill guide.
Photo #1 is the drill block fabricated from a 1-1/4” X 2-1/4” X 6-1/2” aluminum block. The various sized holes are lined with steel bushings to prevent rapid wear of the holes, and the bushings are at least one-inch long to correctly guide the drill bits and reamers.
The #10 hole will guide a #10 drill bit used for all the 3/16” rivet holes. The #14 hole will guide a #14 drill, upsizing the bolt holes for reaming to final size. The 0.1878” and 0.189” holes are for the reamers that I expect to use for the reamed bolt holes.
Photo #2 is the lower clamping block that provides pressure against the lower side of the spar, keeping the laminations tightly clamped while the holes are drilled or reamed. The clear polycarbonate hooks on the ends hold the clamp block loosely in place, so you don’t need to chase it every time you remove the clamps to move the drill block.
Photo #3 shows the drill block clamped in position. The black pin in the #10 hole is a transfer punch that is used to align the drill block precisely over the selected hole before the drill block is clamped in place.
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Drill Block
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Lower Clamping Block
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Drill Block Clamped in Position
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