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Music Wire |
R. W. Stuart Prior to WW2 building model airplanes exposed the builder to steel wire called music wire or piano wire. The wire was produced in many gages to satisfy the requirements of pianos, harps, and other string instruments. It was milled by cold drawing mild steel through diamond dies using tin as a lubricant for the drawing. The resulting wire had a tensile strength of 300,000 psi and a bright (tin) finish which provided some corrosion resistance. It did not bend easily and did not stretch under load as long as the ultimate tensile strength was not exceeded. It could be cut in small gages with side cutters, but tended to put nicks in the cutters. An abrasive cut-off wheel or a couple of angle cuts on a grinder, followed by a squaring grind, was the most practical cutting strategy. The modern available wire (hobby shops and kit material), in the sizes of 1/8, 5/32, and 3/16 diameter, is not the old music wire. It lacks the bright finish and apparently does not have as much ultimate strength. It is, however, a strain hardened wire and has most of the characteristics we need for our work. I see many trips to the picnic table "field bending jig" to straighten nose wheel wires and landing gear wires- the result of the diminished tensile strength combined with "note worthy" landings. A few hints are in order for handling these materials. Do not under any circumstances heat these wires to make them easier to bend- it will do just that and your wire will have all the beauty of a cheap nail. There is no way to reharden the wire consistently, although hammering it on an anvil may return a spotty hardness. Temperatures for soft soldering will not detemper the wire, but if using a torch take it easy. When forming avoid square corners as this may fracture the wire. To bend- hold it in a vice, load it with your hand in the direction you wish it to go. and then crack it lightly with a hammer as close to the vice jaws as you can get. The hammer blows seem to allow the wire to take a set. Soft soldering requires a cleaning and sandpaper scratch up in the area to be soldered, acid flux, and a solid wire (no rosin core) 40-60 solder along with a high capacity gun or iron. A fine steel wire wrapping soldered in will noticeable reenforce the solder job. Neutralize the acid with baking soda water after soldering. |
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