Experimenter

May 2013

Experimenter is a magazine created by EAA for people who build airplanes. We will report on amateur-built aircraft as well as ultralights and other light aircraft.

Issue link: http://experimenter.epubxp.com/i/126719

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wax these tables simply for corrosion protection. It is also common practice in cabinet shops to oil machined surfaces for corrosion protection. Keep in mind that if you mill or saw aircraft wood parts with waxed equipment, you risk contaminating the wood with the wax or oil, and the result might be bad glue joints. These surfaces must be clean and free of any wax, oil or paraffin. This includes the thickness planer rollers. When building with wood, there should always be a barrier between wood and metal parts. Most builders use epoxy varnish on wood and epoxy primer on steel parts. Aluminum parts also can be primed, but this is not always done due to modern aluminum's corrosion resistance. The most common violation is drilling holes through wood for steel bolts. That nice new Sitka spruce will cause bolts to rust if the holes are not sealed. Some varnish and a pipe cleaner work well, but beware of excess varnish in the holes. A reamer sized for the hole may be used to clean out small amounts of varnish from a hole in wood structures. Turn the reamer by hand, and try to do this at a time when the varnish is not fully hard. Remember, you do not want to remove wood, and hard epoxy varnish may be harder than spruce or plywood. If the varnish is in a softer state, the reamer will tend to follow the existing hole. Tape and small, locking pliers work well as a handle. Clean the reamer and wipe it dry after each hole as it will fill with varnish. Another method is to assemble the fittings and then install the bolts with wet varnish. I have done this with conventional spar varnish and have had good results. I'm reluctant to use epoxy varnish here as it just might glue the bolts in place. Regular spar varnish is fine in drilled wood holes as a sealer. Remember that it is not dope proof, which is one reason we use epoxy anywhere fabric is to be applied. The epoxy is dope proof, a luxury early mechanics didn't enjoy. The wet varnish method is somewhat messy but is very effective. As a rule, epoxy varnish is preferred in all other phases. Use cadmium-plated AN hardware and you should be fine. Be sure to pre-varnish under plate fittings and let them dry prior to assembly. Tis plate is from a 1946 Aeronca Champ and shows very little rust because of a good coat of primer. A drill bit sized for the rivet to be driven.  A plastic syringe like this can be used to inject preservative oil in the hole. Using a syringe is an easy way to measure the proper amount of oil to seal the hole. There is plenty of data on wood rot and drain holes, and since it is not my topic I won't go into that here. One last point on wood, though, is about the leaking of fuel and oil. If there's a spill, make sure it is completely cleaned up. Fuel- or oil-soaked wood structures will quickly break down and delaminate. Tubular Steel On tubular steel construction, light oil can be used to prevent rust during construction. Do not use a siliconebased oil as it offers little rust protection, a common mistake. Do not use too much oil; wipe off the area with a clean dry cotton cloth before welding. Once the welding is Photography by Robert Quick A driven rivet is started and tapped in with a small hammer. EAA Experimenter 33

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