brazing bolsters/guards

leifjl

leifjl

Joined
Nov 27, 2011
Messages
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I've been curious for a while about what kind of damage I'm doing to my knives while silver soldering the bolster in place. I have yet to see anyone say anything negative about this process but it seems to make perfect sense that the heat is pretty quickly traveling up the blade. i have'nt noticed a distinct difference in the temper from edge to point but there has to be some loss of hardness nearest the bolster. of course i work as quickly as possible, keeping the heat to a minimum and always cool the edge down after but i have seen a straw temper color come up on occasion anyway. any info would be appreciated.
 
Place the blade in between a couple of big aluminum plates will you do the bolsters. The plates will bleed of the heat.
 
Is there any way to dissipate the heat generated from silver brazing. Not silver soldering, silver brazing. I'd prefer a brazed joint to a soldered joint but the temp. to braze is so high I'm afraid there would be no way to keep the blade cool enough. I have alot of experience brazing , so i can be very precise with the application of heat but theres always conduction.
 
Isn't brazing the same as soldering, but using different materials. Brazing requires brass while this requires silver solder, which has a lower soldering temp.
 
Actually there is silver brazing. Much like brass but, it melts at around 1300f. It would be difficult to keep the blade area cool enough and still get the tang area that hot.
 
"Silver solder" is a term that is misused.
They make low temperature solder that contains 4-6% silver. It is useful for soldering stainless steel, and flows around 400 degrees.
Then there is high temperature silver solder (braze.) I contains no brass, but contains anywhere from 40-70% silver. It flows at around 1000 degress and above. It's much stronger than low-temp solder.

To dissipate heat from high temp silver solder would be difficult. The heat would be drawn off so rapidly, you couldn't get the solder to flow.
 
Use the low temperature solder.

Silver Brazing is sure to damage the HT on the blade. If you could sink the heat enough to not harm the temper at the ricasso, you would not get a proper silver braze. The entire bolster and tang will need to be a minimum of 1000F or above to do the braze. You can't get that temperature in any practical way without ruining something.
 
One thing I've messed with is brazing the guard onto an unquenched blade, then after the braze cools down, use a torch to heat just the edge and quench in oil. The edge won't heat up far enough back to affect the guard joint if there is much of a ricasso.

That allowed me to flow brass into my punched trademark while brazing the guard. It can come out kind of cool.

It all worked, but there are better ways of making a knife- the blade is probably better off quenched as a whole, and certainly better off without the effects of a high spot heat at the guard. I suppose one could heat the whole blade in an HT oven, then pull it out and flow brass into the joint, which would make for a more even thermal effect in the whole blade at the time of brazing.
 
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