1) how do I solder the rod to the bezel + back sheet?;
Butt soldering may do the trick. 2) how do I curve the rod, so
that it looks a stem?; 3) I suppose that the answer to questions #
2 is rather simple if the rod is solid. However, suppose I work
with gold, then a solid rod is too expensive. How can I curve a
hollow rod (tube) so that it looks like I want?
Since you were having trouble finding the answer in a book, here’s a
book answer and ad I guess of my favourite book (The Complete
Metalsmith by Tim McCreight and Silver-Smithing By Rupert
Finegold/William Seitz being the runners up): Jewelry Concepts and
Technology by Oppi Untracht
Page 263 SEAMED AND SEAMLESS TUBE FORMING WITH CORE WIRE AND MANDRELS
. . . {snip}
If a seamless tube is used, force the lubricated wire into the tube.
Its length should be several inches longer than that of the tube so
that the wire is exposed at one end. When the wire reaches the draw
dog end of the tube, the taper can be hammered flat to clinch it
there. The drawing proceeds as usual, and the tube closes down
around the core wire which because it is steel and harder than the
precious or nonferrous metal being drawn, resists reduction while
the other metal is compressed. When the metal lies flat upon the
steel wire core, the correct dimension has been reached, and the
drawing is stopped.
To remove the steel core wire, first cut off the drawing dog end
where the core wire is clinched, to free it. Place the wire that
protrudes from the opposite end of the tube into the front side of
the first drawplate hole through which it will easily pass without
any reduction. With drawtongs, pull out the core wire from the back
of the drawplate. The tube will be stopped when it contacts the
drawplate.
REMOVING A WIRE OR TUBE CORE FROM CURVED SEAMED TUBING The core used
in shaping tubing can be a wire, as described, or another tube. When
bending seamless tubing to a curve with the wire core inside, if the
curve is not too severe, the formerly lubricated core wire or tube
can be pulled out with a drawtongs and drawplate as described above.
With seamed tubing, after curving, some precautions can be taken.
Heat the tube and quench it in sweet oil where it should remain for
15 minutes. With pliers (if the core wire is not already
protruding), bend back the tube at the end to expose the core wire
or tube. Wrap the outside of the shaped tube at the point directly
behind the bent- back part with binding wire. This will hold the seam
together at that point and not allow it to open under the pressure
of removing the core. Then continue as above.
REMOVING A COPPER OR ALUMINUM CORE FROM GOLD TUBE BY ACID To remove
the core after bending gold tubing with a copper tube core, immerse
the tube in a nitric acid solution which will attack the copper but
not the gold. This method takes longer than the extraction of a core
by pulling it out, but is used when tubes have been given drastic
curves that make core removal by other means impossible. Acid entry
is easy when a copper tube has been used as a core, and is used for
large-diameter tube bending.
With this technique, any lubricating grease present must be removed
by heat since its presence would inhibit the action of the acid. To
help the acid enter the tube, drill a few small holes at intervals
along the gold tube. Holes can be soldered closed later. At
intervals lift the tube with copper tongs to drain the acid inside
and allow fresh acid to enter the tube. Rinse the tongs after use.
Aluminum tubing or wire can be used as a core with gold and silver
tubing, as when making hollow gold tube links for a chain. To
dissolve the aluminum, place the tube in a solution of sodium
hydroxide (NaOH), a strong caustic alkali commonly called caustic
soda or lye. This dissolves the aluminum, and its action is faster
if the solution is heated. Wear rubber gloves, and work in good
ventilation. Rinse the result thoroughly.
Page 265 BENDING TUBING When bending tubing, the metal form is changed
beyond its elastic springback limit. The metal weight is
redistributed: the inner curve wall becomes thicker because of
compression and reduction in length, and the outside curve wall
becomes thinner because it stretches. These changes cause the
difficulties experienced in bending tubing. When a tube is not
supported during bending, it tends to buckle on the inside curve,
and the outside curve wall tends to move toward the neutral axis,
which is normally in the’ center of the tube opening when it is
straight but which shifts toward the thicker, inside curve wall when
the tube is bent. There is little stretch at the beginning and the
end of the bend, and the inside shape of the tube at the bend
becomes oval. To counteract this tendency, the use of a core material
Page 266 TUBING makes tube bending with little or no shape change
possible, and it is helpful if the tube metal is in an annealed
condition. The core material acts to support the tube wall and
prevent it from kinking or collapsing during the bending process.
Various materials can be used for a coRe: the choice depends on tube
wall thickness, the diameter of the tube, the bend radius or degree
of bend in the curve, and convenience in use under the particular
circumstances. For bending a tube into simple curves, a solid core
such as wire, or a tube of a smaller diameter which fits into the
tube to be bent can be used. The core material is lubricated with a
light oil so it can be inserted and removed easily. After bending,
the core material is pulled out with pliers. Fast or compound curves
make the withdrawal of solid cores difficult or impossible, unless
the core is of a metal that can be etched out by an acid that does
not affect the original tube. For instance, aluminum can be used as
a core in gold, and etched out with an etchant that only works for
aluminum, as mentioned.
Soluble cores can be used. One such material is hypo crystals
(sodium hyposulphite, Na2S2O4), which is also used as a fixing
medium in photography. This substance is available as a dry,
crystalline salt which is heated to 104B0 F (40B0 C), poured into
the tube which has been closed by masking tape at one end, then
allowed to cool and solidify. It will support the tube during
bending, and because it is water soluble, can easily be dissolved
out of the tube with hot water when its work is completed.
Cores that can be melted out by heat are also possible, and these
include wax, thick grease, pitch, and low-fusible metal alloys. (See
Tapered Tubing, Chapter 7.) Before using them, lubricate the inside
of the tube with oil to facilitate core removal later.
Dry cores such as fine sand can be used, first closing one end of
the tube with masking tape, filling the tube, then closing the other
end with the same material. After bending, the tape is removed and
the sand poured out.
When bending tubing it is important to avoid denting the tube wall
because such blemishes cannot be removed easily, and they cannot be
filed away. One way to prevent the tube surface from becoming
scarred is to wrap it spirally with soft binding wire which keeps
the surface from coming into direct contact with the bending device.
Another possibility is to lubricate the outside of the tube and
insert it into a tight-fitting flexible plastic tube. The plastic
protects the tube surface and to a degree acts as a support when
bending. It is easily removed by pulling it off, or, if the curves
are compound and this is not possible, it can be burned off (in
which case allow for proper ventilation).
TUBE-BENDING DEVICES
MANUAL FORCE Bending the tube in air with the hands is the simplest
way to bend tube, and is possible for tubing without a core if the
tube is of small diameter, but is safer with a core. Proceed slowly,
exert pressure first on the tube ends, if possible. It is difficult
to bend the very ends of a tube into a curve, and provision should
be made for this in cases where it matters by starting with a piece
of tubing longer than the final needed length. Selected curved
portions of the tube can later be sawed away from the rest.
A large-diameter round or tapered tube can be bent manually by first
hammering it with a mallet into an oval shape, then bending it
against the direction of the oval. If the bend is not completed
before the tube returns to a round shape-and it will-hammer the
round to an oval again and continue the bending.
MANDRELS Any suitably shaped round or curved tool such as a triblet
or an anvil, depending on the desired curve radius, can be used as a
shaping device. By manual pressure, press the tube slowly against
the mandrel with the fingers, shifting the point of pressure often
until the tube acquires the desired curve.
HAND PLIERS These can be used to bend small-diameter tubing. Use
half- round or round-nosed pliers, and guard against scarring the
tube by wrapping a piece of leather around it. Proceed slowly, shift
the point of bend, and exert a counterpressure with the fingers to
help form the curve.
A SCROLL BENDER This can be used to bend tubing in the same way as
it is used for scrolling solid wire and flat strip, if the tube has
a core. GROOVED WOOD BLOCK This is discussed below. (See
Demonstration 9 for bending a tapered tube with bending pins, and
see "'Using Wire Without Changing Its Sectional Shape, Chapter 6 for
additional suggestions.)
A TUBE-BENDING BLOCK This steel block has round depressions of
various sizes drilled in its face. A tube end can be bent by
inserting the tube into the tightest opening possible, then bringing
pressure to bear slowly on its end.
BENDING LARGE TUBING WITH GROOVED BLOCKS
The tube must have a core of fine sand, wax, sealing wax, pitch, or
lead when bending it with a grooved hardwood shaping block. These
blocks are easily made, and can contain several grooves in
progressively sharper curves. The very ends of the grooves are
rounded to avoid damaging the tube where it contacts that point.
The fundamental principle involved is one of distributed
counterpressure which prevents tube collapse, most likely to occur
when using pressure at only one point. Insert the tube in the
selected block groove and form the center of the curve first. By
slowly applying bending pressure at one tube end, the other end
becomes wedged in the groove, and the wood block supplies
counterpressure. The pressure brought to bear on the tube must be
sufficient to exceed its elastic limit and set up just enough strain
so that when released, the tube maintains the curve. Sensitivity
must be acquired to detect the limits of this strain. Proceed slowly
and by stages. To shape the tube curve further, shift its position
in the groove, or change it to a more sharply curved groove. The
ends of the tube are shaped last. When the desired curve is reached,
melt out or remove the core material. The same method, in reverse,
can be used to straighten curved tubing, using progressively
straighter grooves in the shaping block. Where a sharp curve must be
made, the tube can be locally annealed at the point where that curve
is to occur. Apply pressure to the stiff parts, and the softer,
annealed parts will bend more easily.
Kindest Regards,
David Woolley
Fredericton, New Brunswick, Canada