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Brian Dougherty

How I solder bolsters to a tapered tang

17 posts in this topic

A few days ago I offered to document how I attach bolsters and scales to tangs that are tapered from spine to belly.  I am sure there are other ways, and probably better ways, but this is what I do.  I use hidden pins for the bolsters, and they are primarily just for maintaining alignment when I solder the bolsters in place.

I have started grinding kitchen knives so that the tang follows the same angle as the bevels of the blade.  I like the look, and it makes grinding much easier. In these pics you can see the angle this creates.  It isn’t much, but it is enough to make drilling for the pins challenging because the standard method result in pins that are not perpendicular to the centerline of the knife.

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The first step is to take on of the bolster blanks and super glue it to the blade.  (I use a lot of superglue as a temporary attachment mechanism)  Once the bolster is temporarily attached, I measure the difference between the thickness at the spine, and the belly.  Divide this number by 2 and you have how much space needs to get made up on each side.

These bolster blanks are quite over-sized.  they will get ground to a taper when I shape the handle.

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Edited by Brian Dougherty

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I make shims out of epoxy stirring sticks.  Usually I just whittle the end down to a bit more than the thickness I want, and then superglue it to the bolster at the same point I made the measurement.  Then I sand it down to the thickness I wanted.  You can see the shim in the red circle…

With the shim in place, I can drill as if the tang were not tapered.  Again, these are hidden pins so I am not drilling too deep in this pic.

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Once the first bolster is drilled, I superglue the 2nd one in place so that it is perfectly aligned with the first.  Then I twist off the first one, make a new shim for the second bolster and drill it like before.

Pic 9.jpg

Pic 10.jpg

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Next I have to make a couple of short pins.  These are just 3/32” brass.  The top one has to be a bit longer than the bottom due to the difference in the spine thickness.  If you do this right, then you can pull the bolster up tight against the blade with a little clamp pressure.  If you mess up, there will be unsightly gaps.

Pic 11.jpg

Pic 12.jpg

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I just use 2% silver bearing solder to hold the bolsters on.  This is a spool bought over 30 years ago when I was a kid soldering together slot-car chassis.  I use it for this because it is a small diameter solder, and it makes it easy for me to keep from putting in too much solder.

The technique is important.  I hold the torch against the bolsters on the spine side, and keep testing the solder in the crevice on the belly side shown in the pic.  As soon as the solder melts, you are done.  Don’t keep feeding solder in, or it will run out along the blade and make a mess that is hard to clean up.  If the mating surfaces are nice and tight, it does not take much solder to get 100% coverage.

In the last pic, you can really see the angle of the bolsters.  I put the scales on in a very similar way, but they get drilled all the way through for cutler's rivets.

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Brian, very informative. I like it when folks share stuff like this it make the learning curve not nearly as steep!!

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Nice explanation!  Are you using a zinc chloride flux?  Or is that flux core wire?

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I use a paste flux, but I've never thought to see what it is.  It's the generic stuff for electronics that comes in a little tub.

Actually, for this demo, I accidentally grabbed a flux/solder paste combo used for plumbing, and it worked rather well.

Edited by Brian Dougherty

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Here are some pics showing the same steps with the scales.  Visually, it becomes more important, because if you don't do something to compensate for the angle, the pins will be noticeably off-center on the second side you drill.  I use these smaller holes for alignment pins during glue-up.  Then I pull the pins out, and open up and counter bore the holes for cutler's rivets when the handle is mostly shaped.

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Since this thread got pinned, I thought I should add a couple of pics that show the finished bolsters:

 

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IMG_4666.JPG

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I really like the process photos, thanks. I do have one question. Why did you choose to eliminate the pattern on the handle profile?

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On 10/14/2017 at 11:20 PM, Joshua States said:

I really like the process photos, thanks. I do have one question. Why did you choose to eliminate the pattern on the handle profile?

Hi Joshua, I'm not following the question.  I'm not sure what you mean by pattern on the handle profile.  Then again, it is Monday morning...

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The blade is etched, but the profile of the blade is not.  The tang sandwiched between the handle and bolsters is polished un-etched steel...

I would imagine it was because everything was fit up permanently a little large and then ground to fit the tang.  

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6 hours ago, Brian Dougherty said:

Hi Joshua, I'm not following the question.  I'm not sure what you mean by pattern on the handle profile.  Then again, it is Monday morning...

It's a Damascus blade, no? The pattern is gone from the spine and belly in the handle.

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29 minutes ago, Joshua States said:

It's a Damascus blade, no? The pattern is gone from the spine and belly in the handle.

Ahh, I understand.  I do the final shaping of the handle after assembly which removes the visible etching.  I've toyed with going back and re-etching after shaping and polishing the handle, but the result haven't been worth doing it.

There have been some examples posted recently of assembling everything before etching, taking the handle apart to etch the blade, and the reassembling as a way to keep the pattern on the visible parts of the handle.  However,  I can't get the parts to fit precisely enough to eliminate ridges/transitions between the parts.   Being able to just barely catch a fingernail on the transition from the tang to the handle just pisses me off, so that method isn't for me.

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Have you tried making a mild steel copy of the blade, shaping the bolsters and scales to the copy, then transferring them to the blade for final assembly?

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