Bolster Soldering Tutorial

[ZDP-189]

I'm no expert myself, but I have some experience here and am working on improving my technique. The following is a description of my current process which seems to work pretty well. It is posted here as much for peer review and comment as to instruct the people who need help.

Equipment

I just use a butane torch. It is the kind you see in cigar lounges that is a little bigger than the mini pocket ones. I have tried larger and smaller ones, but the flame on this is about right on the lowest setting.

In the past I have used silver solder chips or rod, but I find the silver solder paste from Sheffield Supply works best and contains its own flux.

Alternatively, you can braise, but the colour does not match the steel and nickel silver. Don't use lead solder, because the join is a lot weaker.

Preparation

The tighter you can make the bolster fit, the better. Solder won't wick into a gap wider than half a mm. If you get a force-fit, the solder will wick into parts where the gap is widest and along the join. That is what you want.

I use an asbestos braising mat under the vise, because I want to protect my work surface. That's especially important if you are a joiner or carpenter. Then I clamp the blade tip down with the vice holding the ricasso. This shields the blade from the flame and helps to sink away heat.

I used to use Block-It heat shield paste on the blade and ricasso, but it adds no value.

Soldering

I apply the solder paste onto the (clean) join and heat the tang just above the join. The heat will spread down to the join and the solder will amalgamate and run, wicking into the gap. Do not heat the paste directly, as the flux will boil, the solder will ball and you'll ruin the join.

Provided you work quickly and remove the heat as soon as you can, the solder should melt before the blade heats up enough to affect the tempering. There should be no oxidation discolouration on the blade at all.

Some people like to over solder the join and file back to a concave rounded join to the front of the bolster. I suppose that works and would add a bit of strength, but I like to add just enough solder to create just the finest bead, just barely visable. I have found running the tip of a nail, scribe or burnisher around the joint while it is up to soldering temperature will help to spread the bead evenly around the join.

Result

My objective is not to form a supporting structure, but to adhere the joint internally and form a watertight seal to protect the tang from rust over the working life of the knife.

Cautions

Soldering is obviously dangerous. All normal cautions, including the use of personal safety equipment apply.

There are some blades I wouldn't solder. Personally, I'd not solder damascus, as it's sure to need a re-etch. I also wouldn't solder a very small blade where the mechanical benefits of a solder join aren't material and where you could risk affecting the temper over the majority of the cutting edge.

Photos should follow next time I solder a bolster.

[jhobson]

Thanks. Just what I needed to encourage me to have a go ;-)
But maybe I won't be practicing again on my small damascus Poul.

[PS_Bond]

Tuppence worth - I use the newer electronic solders conforming to the WEEE (is that enough E's?) directive. It is a eutectic silver/tin mix AFAIR... Melting point in the order of 230C (need to check that!)

[rapidboy]

I need to solder some stainless.
I have been told to use solder with a 4% silver content.
Anyone know what i need or where to get it.
I am looking at the RS website but it's all a bit confusing !!!

Cheers
rb

[Colin KC]

Melting point in the order of 230C

Wassat in real money then?

[Colin KC]

I need to solder some stainless.
I have been told to use solder with a 4% silver content.
Anyone know what i need or where to get it.
I am looking at the RS website but it's all a bit confusing !!!

Cheers
rb

Sorry RB, don' know

[PS_Bond]

I'll try and post a suitable stock number when the site isn't down...

[Kevin]

Thanks for telling us the way you solder..

You mentioned tight fits and clean joints...crucial.

I hold my tang in the vice (opposite to you), blade up. To stop the guard from slipping down the tang, I get a small centre punch and pop the tang side of the guard so it tightens the guard against the tang.....

I wrap some damp kitchen role paper around the blade as a heat soak..just in case.

I apply the heat from the top (ricasso side of blade) and apply the solder from underneath (tang side)...the solder will always want to flow to the heat by a capilary action.......It suddenly just appears around the join..and no risk of it spilling out.

I often recess my tang ever so slightly where the joint will be...so the guard is sitting on shoulders all 4 sides.....but I taper my blades and tangs so it leaves the ricaso the thickest..so leaves a lot of steel to do this without weakening anything..It can make a good looking fit and joint if done right. I prefer not to see any solder joint showing..or as least as possible...so I then shave off any access solder with a 1/8th inch copper pin, which I shaped into a chisel.....being copper it will not scratch the steel or guard....I also heat the copper chisel just slightly and the solder slides off.

I have successfuly soldered a damascus blade with a nickel silver guard........I did all the soldering before I etched the blade to show the pattern.......and cleaned up as normal.....
Then when its time to etch, I painted the guard and joint with blue dye first...this protected the joint and guard from etching. After etching the blade, just clean the dye off with some alcohal.

[PS_Bond]

RS s/n 362-8061 - 95·5% tin/ 3·8% silver/ 0·7% copper alloy with eutectic melting point of 217°C
£17.10 ex VAT for a 500g reel

(or for Colin - 422.6F, 17.6Oz - http://www.onlineconversion.com/ )

[lilzee]

i've succesfully done it a few times, but i always use waaaaay too much, and have to fileit away off the top of the guard, i always scratch up the ricasso,

any way to tell when you have enough on there r some way to protect the ricasso?

[narsil]

If you're having a problem of solder getting where you don't want it you can use a yellow ochre paint as a solder resist, solder won't flow onto anything which as the yellow ochre on it.

Another option for large flat joins is to sweat solder. ie melt the solder onto one surface first (the bolster in this case) then flux both surfaces, fit the bolster and then re heat to form the join.

[lilzee]

hmmm, that's cool about the paint. thanks chris.