Will W.

Having problems soldering guards

29 posts in this topic

Dry ice is roughly -109f, hardly cryo. 

Interference fit joinery is old, OLD stuff and a couple thousandths isn't enough to cause the guard to fail. NO sharp inside corners. Right? 

I'll bet you dollars to donuts you can solder SS to HC steel at temps that won't damage the heat treat. It'd take research I'm not interested enough to do but here's how I'd solder the two. Dissimilar metal joinery of this sort is accomplished by tinning the higher temp piece with a solder that can be soldered to by a lower temp solder.

Solder A is a high temp SS solder you use to tin the inside of the SS part. Solder 2 is suitable for soldering HC steel at a temp low enough a heat stop will prevent it altering the blade's heat treat. The guard is slipped over the tang, the tang is heated ad solder 2 is sweated into the joint. The heat stop prevents heat conducting past the guard into the blade.

Or you could cheat, plate the inside of the guard and outside of the tang with copper and use a common solder.

This is metal shop 2 joinery. 

Frosty The Lucky.

Share this post


Link to post
Share on other sites

Granted it's not as cold as liquid nitrogen, but it's still considered cryo and as long as you get the blade below -100 deg. it's still doing it's job.  I did not say it would not work, just that I would not risk it with stainless, or carbon steel for that mater, as blades below -100 are very brittle, and the sudden temp change of a hot guard could cause a fracture at the junction, and if you decide to give it a little tap to seat the guard it could fracture as well.  20-25 degree in the kitchen freezer on the other hand will cause enough shrinkage to allow an interference fit with a guard that has been warmed to 200 deg. in an oven to slip on without undue stress to the blade, or taking skin off while your doing it.  This is supposition from not wanting to break a blade and not taking chances on something I've got a couple days work in.


I was talking about silver braze, not solder, ruining the heat treat and unless you can find a braze that will remain solid at 2000 deg then don't do it before heat treat either.  Silver solder, or low temp solder, is fine, and done rite will not ruin the temper of most any knife out there.  Most times I simply wrapped a wet paper towel around the blade to prevent heat transfer if needed.  There are various low temp solders out there, but I don't know of any off hand that will flow at below 350 deg. and work and look rite for a guard, but it wouldn't surprise me overmuch if they exist.

Share this post


Link to post
Share on other sites

I see, it's cryo for the blade makers, not in the lab sense of the term. Okay.

Silver braze IS solder by definition then again it's old school definition and it's been 45 years since trade school for me. Braze is or was a specific term referring to using bronze as a hard solder. Later it was widened to include brass. "Silver braze" seems to have come about in recent years when there was already a perfectly good term that covered it. "Silver Solder" I think there were guys who couldn't wrap their heads around or just didn't know what "solder" means.

Soldering is a process of joinery where a metal with a lower melting temperature that can form a molecular surface bond is introduced into the joint. When solidified the joint is as strong as the solder. This is why it behooves you to match the surfaces as closely as possible for as thin a layer of solder as possible. 

If you wouldn't sweat an interference fit with SS, Don't.

This conversation has devolved into semantics I spent too many years in school learning the trade. Call it what you will.

Frosty The Lucky.

Share this post


Link to post
Share on other sites

I understand the difference, but the terms solder and silver solder and silver braze is used so indiscriminately now to describe several different heat and strength ranges that I ask for heat range any more instead of silver solder or braze just to be sure of what I'm getting.

You are correct that -100 is not cryo in the proper sense of the word, but knife makers usefully use the term, incorrectly, for dry ice and kerosene as part of the heat treat.

I never said I would not do an interference fit, just that I'd be cautious about it, namely that there is little reason to go -100 deg. when kitchen freezers will shrink it enough and not risk damaging a couple days work.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now