I need to securely join a 3 inch length of 1/4 inch threaded rod co-axially to a 1 inch length of 7/16 plain bar. Two methods under consideration are a) drill and tap the 7/16 bar then silver solder the threaded rod in place or b) drill the 7/16 bar, turn the threads of the rod, insert and silver solder. Any comments on difficulty of silver soldering stainless (will probably be type 304 or similar). Would Loctite work with method b), if so which type? TIA for any constructive comments. Ray
I can't speak to silver soldering stainless; I do it on copper and other non-ferrous stuff with aplomb. But #304 brazes elegantly well, so I'd suspect it will silver solder with the right flux.
============ Why not thread the end of the rod and fabricate an adapter? Use red [threadlock] loctite.
Carefully drill out 7/16 rod to 1/4 inch and red loctite.
Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.
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I don't know how much strength you need but IMHO the strongest method would be to silver braze the pieces without any threads at the joint. In other words, drill the bar for a slip fit and insert the unthreaded end of the 1/4" rod. Flux and heat the pieces until the flux melts, then add silver sparingly until a small fillet of silver forms at the joint. Use a high silver content brazing material (not Silfos 5 or
15).
It might be difficult to get silver to wet down through the theads and penetrate the joint adequately.
The key to silver soldering stainless steel (my experience lies with the 300 series austenitic type) is cleanliness AND the right flux.
For flux I use Handy and Harman "Handy Flux" for low temperature brazing, "active between 565 deg. C and 870 deg C."
Specifications read: "Based on Federal Spec O-F-499D (typeB), SAE-AMS
3410G, AWS Class FB3A."
It contains FLUORIDE compounds which are necessary to dissolve the tenacious and heat-resistant chromium oxide layer for the solder to wet the stainless steel.
Good ventilation is necessary when using this stuff, AND, remove all flux residue immediately after soldering....this is imperative since this flux gives rise to inter-granular corrosion in the stainless steel.
Use a propane torch for silver soldering.....O-A is too fierce and the likelihood of overheating the metal is greatly increased. Particularly on stainless steel overheating creates a mess that is time consuming to clean up.
Pre-placing the silver solder permits you to observe when the right temperature has been achieved: the solder is drawn by capillary action into the joint, leaving a tiny fillet. With proper fit-up and hot clearance of about .002" per side the joint is stronger than the parent metal.
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