When joining piano wire, especially for high stress areas such as under carriages, by far the best material to use is silver solder, compared to soft solder it makes a much stronger joint and because it doesn’t need binding for added strength the result is neater and less bulky.
As in the rest of life “you get nowt for nowt!” It’s more expensive, requires more heat (a blow torch of some description) and the work pieces usually need to be jigged, but believe me the extra work is well worth the effort.
The flux used is “active”, that is when heated it actually cleans the metal to which it has been applied. This doesn’t mean that you shouldn’t thoroughly clean the joint before applying the flux, but it does mean that a perfect joint is virtually guaranteed every time.
The flux can cause a problem, where as any engineering supplier will gladly sell you just one length, approx. 40cm., of silver solder they usually only sell the flux in bulk but it is available in small quantities via. Mail Order from
www.proopsbrothers.com.
The most suitable silver solder for our modelling use looks like 16swg piano wire, but don’t get it mixed up, you’ll never melt piano wire and silver solder make an expensive throttle linkage! Talking of expense the price seems to vary greatly, not from supplier to supplier but over time, perhaps tied to the international price of silver? Therefore, if you find a “cheap” batch it might be worth buying more that you need immediately, I do.
The piano wire can be bent as per plans, although the joints don’t really need to be as large, then some form of jig made to hold the pieces in place whist soldering. I use scrap pine and various wood screws etc., the wood may char but so long as you take reasonable care with the flame it won’t ignite.
The best way is to mix the flux into a paste and apply it to the joint before any heat. Many years ago, before Health and Safety and Political Correctness, my metal work teacher at school said “just spit in it lad!” I don’t know if saliva has some magic ingredient but in my experience it makes a better flux paste than tap water.
Apply heat to the part to be soldered and as soon as the flux melts start to test the temperature by applying the solder. The ideal temperature is indicated by a dull red colour, too high a temperature will cause the piano wire to lose it spring, let the joint cool naturally, if you quench it with cold water the wire will become brittle.
Continue until all joints are soldered then clean off the flux thoroughly, any excess solder can be ground off without fear of the heat generated melting the join.
The result is one strong under carriage that will take all the punishment you can give it.
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