I don't believe you're going to have any reliability concerns using copper.
I know plenty of people who use pure copper for Japanese blade fittings, including habakis, and I'm pretty certain that type of application is a tad more demanding than a lanyard tube.
As to the use of copper for Corbys, keep in mind that both pure copper and copper alloys (including brass) work harden.
With the exception of high heat for annealing purposes, just about anything physically done to the copper (or copper alloy) will harden it.
The only process that will soften it again is annealing, and I highly doubt those Corbys are annealed after being machined.:biggrin:
Yet another consideration is that you're not torquing down a cylinder head. You're installing a set of knife scales.
There may be some who disagree with me, but in this case, my belief is that the fastener should be viewed more as an aid to alignment rather than as a clamping mechanism.
Some people like to forgo use of epoxy when using Corbys, preferring instead to use the fastener as an integral clamp. That's fine, except for the fact that if the scale material itself is not stable (e.g., wood), fastening strictly via mechanical means will probably leave the maker scratching his head at a later date when the minute expansion/contraction leaves a loosened item. And in the case of Corbys, there is no simple method of re-tightening since the means to tighten has been eliminated (slots ground off).
For this reason alone, I would use epoxy to lock the threads in place before finish grinding.
The point is, don't worry about the "strength" of your Corby threads. Use an epoxy as the primary means of attachment strength, and let the Corbys be an alignment aid with visual appeal. When you approach it this way, you don't need to worry about thread reliability; if you're stripping threads, you're over-tightening it.
How long have people been using pins? No great clamping pressure there either, but they work just fine with epoxy.
(As a side note, the use of epoxy also helps alleviate concerns over galvanic corrosion between dissimilar metals, but that's another story with a bunch of variables.)
So now that your concerns about copper Corbys are put to rest, what about tubing for lanyards?
Use whatever you want. You said you wanted the visual contrast, so I would go with thick-walled tubing, but thin-walled will be just as functional. After all, how many knives out there have no tube at all- just a simple drilled hole?
For patinas, James provided an excellent link. If you don't want to experiment with making them, a jewelry supplier can hook you up.
One concern here- final installation of the tube into the handle. The order of your finishing methods may be such that an applied patina is sanded/buffed off. In this instance, the patina should be the final thing to be done, but different chemicals react differently with various handle materials. Run a sample test first to determine compatability, checking for adverse effects. Great, now I just sounded like a laundry detergent manufacturer!
Good Luck,
Rob
