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Soldering bezels to large flat backplate


#1

I am new to the forum & hope someone can help me on this one. I am
soldering large gold bezels (14ky or 18ky) to a gold backplate and
have had problems getting the solder to flow cleanly & completely.
The bezels are made from 24g to 28g, from 30mm x 40mm to 50mm x 70mm
in diameter and the backplate is always 20g. I use a Meco torch w/
oxy-propane @ 14lbs oxy & 7 lbs propane with not tip, and set the
backplate & bezel on a heavy heat screen. I make sure that the
metal is super clean & that there is no gaps between the metals. I
use boric acid/alcohol for the coating & use Battern’s Flux (yellow
liquid flux) to solder, placing small balled up medium solder on the
inside of the bezel. Using this method for smaller bezels (20mm x
30mm), I have no problems but for larger pieces the soldering
results are horrible. It seems to me that maybe the piece isn’t
getting hot enough but I have encountered a problem recently with the
metal completely alloying into the steel heatscreen (a $300 materials
accident). I have thought about using my casting torch w/ a rosebud
tip but am a little afraid to do so. I do heat the piece evenly and
outwardly to draw the solder from inside the bezel diameter out. Am
I using the wrong flux or techniques? Help Please. Thank you in
advance. Michael


#2

Michael, It sounds like you are doing almost everything correctly
except one.

From you description, you are placing the material on a heat screen
…probably on a soldering plate or something?

Soldering items that large requires virtually ALL the heat be
directed at the largest heat sink part…the base plate. On a screen
you can get approximately 30% of the heat to the bottom, the rest
goes into the bezel, top of the plate and the screen.

Try this. Stand two charcoal, magnesia, or alumina blocks on end
about 6 inches apart. Place the screen across them and the piece
being soldered on top of the screen. Now, heat directly from
underneath. With this configuration you will get 80% of the heat
onto the bottom of the plate with the remaining 20% going into the
screen. The blocks will absorb very little heat and reflect part of
that back.

I couldn’t tell from your post what tip you were using but in any
event, use a large bushy flame and keep only the tip of the flame on
the piece…gradually bringing it closer until the piece begins to
show dull red. Stop at this point and it will continue to redden
until the solder flows. Immediately remove the flame.

Let us know how it works. Cheers from Don at The Charles Belle
Studio in SOFL where simple elegance IS fine jewelry!
@coralnut1


#3
 I am soldering large gold bezels (14ky or 18ky) to a gold
backplate and have had problems getting the solder to flow cleanly
& completely. 

I am doing this on silver, but my method to deal with this very
problem is to use a little “ultralite” kiln, sold by Rio, etc, for
around $100. It looks a little like a small frying pan made of
refractory ceramic. It will keep your whole piece evenly hot from the
bottom, almost to soldering temp. I then find it easy to melt and
draw the solder with a pretty small torch flame, which you can use
right on the kiln (this is the type of open kiln often used for
granulation). HTH! --Noel


#4

Interesting place, Orchid… Two postings today remind me of the old
days…This being one. I used to do a fair amount of large silver-
12" long boxes, pieces weighing 6 or 8 ounces, and even up to a
couple of pounds. First, as to heat, get a tripod- the kind that
mates with your heavy screen, and put the screen on it, and then your
work. Do all the major heating from underneath, until it’s
essentially AT soldering temp., and then go on top and flow
everything with the flame. (Probably/typically) you are burning up
the flux and trashing your solder with all that flame, before you ever
get to temp. Even better, if you have a kiln, put it in there on the
screen at about 1000f, pull it out and finish it off. For that kind
of work, we would use wire solder 3-4" long, in insulated tweezers and
just flow it on. If it gets sluggish, stop, pickle, rinse totally,
and start over- it will flow like gangbusters 2nd time around.
Lastly-Why are you using med. solder? Never owned any myself…


#5

Michael, It sounds like you are doing every thing correct. I would
suggest using a fluoride based flux such as Handy Flux. This will
help the solder flow in seams. It works so well that you can
actually put solder on at only one spot.

Also, if you can find another way to hold the piece other than the
screen that may help. It is certainly acting as a heat sink which
could only have a negative reaction in this case.

John Sholl
Littleton, Colorado


#6
Am I using the wrong flux or techniques? 

Hi Michael. Wrong techniques! What you’re doing will work for
silver which is a great conductor of heat, but not for gold which
isn’t. With a larger gold bezel, trying to heat the whole piece
evenly is usually counter-productive – especially with such thick
base metal (I use 14K 28 or 26 gauge backing with 22K bezel wire).
By the time you’ve moved the torch from one side of the bezel to the
other, the metal is already cooling off on the first side.

So, I’d consider using thinner gauge backing metal; it’s not quite
as difficult to get hot (and not so expensive either!). Did you say
50-70 mm?!? Wow, that’s big! Still, 24 gauge (certainly 22) might
work without warping too badly. Next, I’d get rid of the heavy
screen which is acting as a heat sink and making it even harder to
keep the gold hot.

Here’s what I’d suggest: Put the piece on a charcoal or "magnesia"
block; both absorb heat and will assist in getting the metal up to
temperature. Warm up the entire piece somewhat and then focus on
trying to tack the bezel down at, say, four opposing points. Don’t
worry about flowing the solder yet; what you want to do is stabilize
the bezel so it won’t move.

Once the bezel is tacked down, do one of two things. 1) Put the
piece in a third hand so it’s suspended. You’ll need to find
something to prop up the third hand’s tweezers so the assembly won’t
move. 2) (Assuming you’re right handed) hold the piece in tweezers
with your left hand and keep the torch in your right. It’s okay to
have one blade of the tweezers on top of the bezel and the other
under the sheet; just be sure not to squeeze too tightly! A
cross-lock tweezers is usually okay. A self-locking tweezers will be
too tight.

Note: If you pre-placed all your solder chips (I do it inside the
bezel) and fluxed sufficiently (I prefer Cupronil but there’s
nothing wrong with Batterns) and didn’t overheat the piece and
you don’t let the piece cool off too much while you’re repositioning
it, you should be able to keep soldering without refluxing.

If the metal has cooled off, you’ll have to reflux. If you didn’t
use enough flux in the first place or overheated to the point that
the solder joints have developed scale, you’ll need to pickle to
clean the metal, reflux and replace your solder chips before
proceeding.

Now, with the piece suspended, you can reheat from the bottom (less
chance of melting the bezel and better chance of keeping the heat
focused). Flow the solder between two of the tacked points, then the
next section, etc., until it’s done. You will probably have to
reposition the piece at least once so you’re able to solder the side
that the tweezers were on in the first place.

Note: You could not in most cases do this with silver. If you
suspended a large piece of silver this way by a corner and then
heated from below, by the time you got the whole piece of silver hot
enough for the solder to flow, the sheet will have slumped. Since
you can “spot solder” gold, without needing to heat the whole piece,
you can avoid this problem if you’re careful.

I’m sure you’ll get other suggestions and you’ll want to experiment
to see which works best for you. There isn’t just one right way.
Good luck.

Beth


#7

Michael and Beth Beth is so right about the differences in soldering
gold and silver. My original inclination in my post was to suggest
the ‘air’ soldering technique Beth describes (I use it all the time)
however, the large size of the pieces you are soldering mitigate
against using tweezers to hold the item. This is, I believe, double
trouble because of the thin bezel material you are using. ANY
pressure against the top of the bezel coupled with heat, even if
it’s from below, will probably result in warped bezel. The weight of
a 50x70mm piece is just too much to hold in common tweezers…you
can make special ones by brazing a circle onto one tine for use as a
support, but even then the weight will be hard to control.

For these reasons, I still suggest you try the block and screen
bridge as a support for the work. I should have probably mentioned
something Beth picked up on as well. It is not necessary to bring the
entire piece up to red when soldering gold. But, because of the
large size, I would still use a bushy flame to ‘condition’ the entire
base plate so you can assure there is no warping between the plate
and the bezel. Then, you can concentrate the flame on one area under
the bezel to get solder flow after which you simply move the torch
along under the bezel. Each snippet will melt and flow as you move
along until the circuit is complete.

Cheers from Don at The Charles Belle Studio in SOFL where simple
elegance IS fine jewelry! @coralnut1


#8

Hello , I use the same torch / fuel /pressure as you do and same
flux/prep . There are 2 schools of thought on large scale gold
soldering . You are trying to do the “large flame get all hot at
once school” and the steel heatscreen is absorbing too much heat . I
use the " small flame local soldering technique" I would probably
use a 3rd hand or two and support the piece in the air . Using the
32 [ or possible 40] tip [I believe these are NG tips , but I prefer their flame characteristics they look like a straight cone nut to tip ] I would seek to solder in small sections , say 1 cm. or so
at a time and continue around until all soldered , if there is
irregularity , after pickling re-heat perhaps using the no tip for
large flame and you can flow all solder at same time . The tricky
part for me is always getting tjhe initial “tack” established , and
this is where the contol afforded by the smaller flame is useful . [
note this local vs. large soldering concept applies to gold and
plat only , silver conducts heat way too well you must heat entire
piece ]

Hoping this helps ,
Mark Clodius
Clodius&Co. Jewelers


#9

I solder findings on sterling buckles, conchos and pins. I support
the main piece between two blocks. I heat from the bottom side of
the piece with an upward point flame. The findings are on the top
of the item. When the temperature of the main piece is about at the
solder temperature I move the torch to the top of the piece and heat
the findings and main piece with a brush of the torch. The motion of
the torch will prevent the bezel or finding from melting. I use a
sharpie pen to mark a strip on the top side of the piece. I find
that when the strip starts to burn away the temperature is almost
correct for medium solder. I use acetylene and a large tip. I try
to heat the silver as fast as I can.

To prevent fire scale I coat both sides of the piece with an
anti-fire scale flux. I find that handy paste flux is best at the
solder joint. Do not use too much paste flux as it will spread and
wash away the anti-fire scale coating.

I normally do not solder small items. I discarded the metal solder
screen many years ago because I found it difficult to get enough
heat on the piece. Good luck. Lee Epperson