# Air holes for soldering

Does anyone have theories regarding the size/placement/number of air
holes needed for safety when soldering closed shapes? An example:
Imagine a cylinder 25 mm tall made of 0.5 mm sheet and closed on
both ends with 0.5 mm sheet. Put an 8 mm hole in each end and stick a
tube (25 cm long; 8 mm ext. dia. with 0.5 mm wall) thru the tube.
Solder the tube and the cylinder together. What is needed in the way
of air holes (size/placement/number) in the part of the tube which
lies within the cylinder in each of these situations:

1. The tube is open at both ends.

2. The tube is capped at both ends, and one end has a 2.5 mm hole.

A colleague of mine says there is a BIG difference between one
2mm-hole as opposed to two 1mm-holes. Do you agree?

Another factor is if you solder only one end of the cylinder to the
tube leaving the second end with a tight (but non-hermetic) fit. Is
the amount of air that can escape through a tight, unsoldered fit
significant?

There are of course MANY factors in determining safety air holes:
size of closed shape, thickness of sheet, relative proportion of size
of shape to thickness of sheet, complexity of the total item (how
many such shapes are connected), etc. My present project involves
three closed shapes (cone, cylinder, and triangular ‘cylinder’)
soldered to a tube whose outer diameter goes from 6mm to 8mm to 5mm
to 2.5mm. Each soldering will require multiple considerations, but I
was hoping someone might have some general principles…Failing that,
theories regarding the above examples would be of great interest.

By the way, there will be two more closed shapes (dome and sphere)
on the tube. They will be threaded onto the tube last, and then the
whole complex item will be closed with a 2mm-diameter screw into the
open end of the tube).

Janet in Jerusalem

I do not know if I missed something but what material is it that you
are soldering? It is possible to solder closed pieces depending on
the media. Work hardened gold objects tend to be OK depending on
thickness. One thing to consider also is at what stage for final
solder, has it been pickled, if so needs to be cleaned and dried and
if dipped in anti fire scale solution heat it slowly to allow gasses
to escape. If in unsure small hole will not be a problem just make
sure nothing is left inside to cause anti solder fumes, acids tend to
sizzle and keep solder from filing seams. The size of the gas escape
hole in my opinion is not size related unless it is to small to see.
A lot of commercial hollow objects have small holes for gas to
escape.Correct me if I am wrong. I have had bad experience with
hollow silver in the past at the bench on repairs at the beginning of
my bench life where they would expand and puff out, quite freaking
but now I know a little hole, clean and dry.

``````A colleague of mine says there is a BIG difference between one
2mm-hole as opposed to two 1mm-holes. Do you agree?
``````

Formula for area of the circle is Pi times radius squared. 1mm would
have 3.14 * 0.25 = 0.785 Two such holes would be 1.57 of combined
cross-section 2 mm hole would have twice as much area ( 3.14*1)
Because of the radius been squared, the values of cross-sections
would increase geometrically. Doubling of the radius, would give 4x
increase in cross-section. Therefore one would need four 1mm holes
to equal one 2mm holes.

Leonid Surpin

I forgot to say the tube is about 25 centimeters long…

Janet in Jerusalem

I can’t believe I forgot to list the material…;-p…!!! It’s
sterling silver…:-)…

Leonid: Any ideas regarding size and placement of holes…

Carl Burris wrote: “The size of the gas escape hole in my opinion is
not size related unless it is to small to see.” This is definitely
not true…:-)…Perhaps the most important considerations are the
size of the closed area, the thickness of the metal, and the amount
of heat(ing).

Janet in Jerusalem

My vent hole is usually 2mm. Default as that is the most common
drill bit that I have.

John
Rasmussen Gems & Jewelry LLC

``````Leonid: Any ideas regarding size and placement of holes..
``````

0.5mm is just fine as long as you heat slowly. Place it anywhere it
is convenient for you.

Leonid Surpin

Hi Janet,

The breather holes are most needed if there is a chance that water
can get inside the enclosed space. If you solder the enclosed space
completely tight with no pinholes or even the slightest fissure then
there will be no moisture inside the enclosed space after pickling
and washing.

The main danger is moisture entering the space after the soldering
is done. After soldering, the interior space will be completely dry
but there is a vacuum that will suck in pickle and washing fluids if
there is any possibility of them getting in. It won’t be a complete
vacuum, just the difference between the atmospheric pressure of air
at room temperature and the soldering temperature.

You never know what happens years later such as someone dunking the
item into a hot ultrasonic and then rinsing in cold water. This will
suck in moisture if there is any way it can get in. If the item
contains a small amount of moisture then it can go ‘poof’’, burst,
or explode upon further heating.

So there are two options…

1. Have no breather hole and make sure the enclosed space is 100%
watertight. If you re-heat it years later then do drill a breather
hole before heating… do this when heating any enclosed space that
you are not sure about. The hole can be soldered closed afterwards.

2. Making a breather hole will automatically allow moisture into the
cavity including pickle and washing fluids. Take care to nutralize
and rinse out any pickle and dry thoroughly by gentle heating. The
sudden rush when the moisture turns to steam upon further heating
means the hole must be big enough to vent the steam as well as wads
of lint, earwax, and whatever else may have gotten inside.

Alastair

The issue about having a hole is that air expands when heated. If you
solder something and trap air, if you have more soldering to do, the
piece will explode, it is really loud, it is right in your face, and
I had a bit more adrenaline running around after the first and only
time I did that. If it is not airtight and you pickle it and pickle
gets trapped inside, when heated the pickle turns into a gas and
forcefully steams out the hole. Unpleasant and unhealthy.

I use one or two drill holes depending on the size of the object.
When I do not want to have drill holes after I finish the piece,
after I have finished all soldering, I use a hypodermic syringe to
force water with baking soda added to get all the pickle out. I ball
up the metal I working with, put some solder on the ball, and solder
the hole shut, or I hammer the ball flat, apply solder to one side
and solder that over the hole. I can file the ball flat or use it as
a decorative element. You can also have a square or circle and have
your hallmark or karat stamps on the final part soldered. I do not
have any problem soldering a ball to cover the drill hole. When the
piece heats up the air expands and after the solder flows, the hole
is sealed. If that is the only place air can enter or exit, as it
cools, there will be a vacuum created. I do not quench immediately.
If you are not sure if it is sealed, you can very gently heat the
piece and see if it starts producing steam. It will not take much
heat to start steaming.

If you are making a pin/pendant, the drill holes can be where the
pin findings are soldered to the piece. This is where I flatten a
ball, solder the pin finding to the disc with hard solder, solder
the disc to the piece with easy solder.

Richard Hart G.G.
Denver, Co.

ALASTAIR said:

``````The breather holes are most needed if there is a chance that water
can get inside the enclosed space.
``````

The holes I refer to are not to keep out moisture–they are to let
expanding (heated) air escape in order to prevent exploding on
subsequent solderings…

JOHN RASMUSSEN said:

``````My vent hole is usually 2mm. Default as that is the most common
drill bit that I have.
``````

What size closed forms?

LEONID said:

``````0.5mm is just fine as long as you heat slowly.
``````

I always used .50 on jewelry too. My colleague who does BIG
hollowware says it needs to be 2mm (very big for me) on larger
objects…(?)

Richard Hart

Thanks for your response. I have always done air holes the way you
do. down to the hypodermic syringe to force water with baking soda
added to get all the pickle out. But the question was regarding the
size and placement of holes on a much larger object. not
jewelry…:-)…

Janet

Richard: Carlene Hughes, a lovely Denver silversmith at Hyland Hills
Rec Center, had the experience you describe of an earring blowing up
on her while she was trying to repair it. I am going to work on a
hollow earring repair for a client and appreciate your precise
instructions as well as the contributions of other Orchid members to
this thread. I let the customer know that there was much discussion
to drill a hole in her earring to prevent it from blowing up.

Thanks, Betsy

``````But the question was regarding the size and placement of holes on a
much larger object. not jewelry....:-)....
``````

I think the larger part of the issue of what holes where is for
removing pickle from the object, not about

concern for how the air will escape. An air hole is not needed once
you solder an object shut, only if you are going to do more soldering
on an object that is sealed.

When a metal object with air contained within is heated, the air
expands quickly…5mm-2mm was mentioned. I do not know what “a much
larger object” is, but how quickly a larger object can be heated
factors into the answer. However, since air offers little resistance
to escaping from an enclosure, it does not take much of an opening to
allow air to escape, regardless of how fast the object can be heated.

I once soldered something thinking it was sealed, and an incomplete
solder seam that was not visible to the eye allowed pickle inside the
object. Then I had to drill a hole to allow the pickle to be
removed.

Where I place the holes are for practicality for allowing rinse
water to circulate to remove pickle in relationship to how the holes
affect the design. Most holes are placed on the back of an object,
so sometimes top and bottom, sometimes on either side.

I have used only one hole and a hypodermic needle inserted into the
hole provided enough pressure when the water was forcefully injected
to force the pickle out around the needle.

Richard Hart G.G.
Denver, Co.

Hi Richard,

``````"I think the larger part of the issue of what holes where is for
how the air will escape."
``````

I’m afraid I would have to disagree with that…A hermetically
sealed form is prone to explosion upon heating even if it contains
no moisture at all! Heat expands. Like yourself, I too am used to
working more on jewelry-sized pieces, and I also thought it might be
the case that as long as there’s a hole (I usually use 0.5 mm), it
would be OK. But my friend, who has 40 years of experience with very
large, very complex items, was adamant about the fact that even 1mm.
holes would be nowhere near enough to be safe! He speaks from
experience…:-)…

All the Orchidians who have replied to my post have given accounts
regarding how they deal with this issue in jewelry. They all do
pretty much what I have always done and, like myself, made
assumptions based on that experience. I was hoping to hear from
folks who, like my local friend, work primarily with objects much
larger than what jewelers typically do to see what their experience
has shown. As mentioned in my original post, my object is a
12"/30cm. tube of changing dimensions with five closed objects of
different shapes and sizes soldered on to it (dimensions in first
post). That’s certainly not huge, but I think it is large enough to
require different handling from a jewelry item. I was looking for
real-life experience rather than theory based on experience similar
to my own…:-)… Anyone…

Janet

Janet,

``````I'm afraid I would have to disagree with that....A hermetically
sealed form is prone to explosion upon heating even if it contains
no moisture at all! Heat expands >As mentioned in my original post,
my object is a 12"/30cm. tube of changing dimensions with five
closed objects of different shapes and sizes soldered on to it
(dimensions in first post).
``````

So if the first part you wrote is true, how did you solder 5 closed
objects onto a tube referred to in the second part you wrote? If you
re-read my post, I said that a sealed object needed an air hole if
any more soldering was going to be done.

An object that is soldered shut could not contain any moisture.

A sealed object is not prone to explode, temperature required to
solder guarantees an explosion.

It is not clear to me what your friend is doing. Is your friend
goingto solder a large object shut and then do more soldering? How
large is the object? Is it going to be pickled?

Richard Hart G.G.
Denver, Co.

``````All the Orchidians who have replied to my post have given accounts
regarding how they deal with this issue in jewelry. They all do
pretty much what I have always done and, like myself, made
assumptions based on that experience. I was hoping to hear from
folks who, like my local friend, work primarily with objects much
larger than what jewelers typically do to see what their
experience has shown. As mentioned in my original post, my object
is a 12"/30cm.
``````

I have worked with larger hollow pieces, though not as large as your
discussing. It’s not really possible to extract an exact hole size
unless you can calculate the rate of heating (and therefore the
changing volume of expanding gas) and the pressure it would apply to
the solder seam in it’s weakened (liquid) state or against the wall
in it’s weakened state. On smaller production pieces like large belt
buckles 1mm holes are too small. We used 2 holes 2.5 mm and up to 3
mm on larger objects. Again how rapidly you heat the piece is a big
factor. I believe that if you were to do this in a production
setting with multiple torches you might consider 2 holes as large as
6 mm. If you are using one torch, then you could probably go smaller
maybe down to 3 mm. The holes should not be placed so the flux would
flow into them and clog them. Even larger holes can be blocked enough
to cause deformation on a piece. If this is a one time piece that you
are afraid to damage, you have to go larger and them cold close them
latter (another discussion) if needed. With careful planning it is
possible to solder a hollow form, without holes, and without
deforming, it’s just hard to do.

Just a side note. A piece this large without holes once finished
could be deformed in the heat of the sun on a hot day, dependent on
the wall thickness of the material of course.

Dan Culver

``````But the question was regarding the size and placement of holes on a
much larger object. not jewelry....:-)....
``````

P.S. I believe that the gauge of the metal has a bearing on whether
a hermetically sealed object will explode. The thickness of the metal
verses the amount of pressure heated air can exert.

What is the gauge of the metal of the large object?

I have never made a hollow object with anything more than 24 gauge.
Use 14 gauge and I believe the results would be different.

Richard Hart G.G.
Denver, Co.

Janet, my only real life experience was a high school science class
where a one gallon tin can was heated, then sealed, and upon cooling
the can collapsed slightly due to the difference of atmospheric
pressure between the inside and and the outside of the can. In
today’s high school slang, coolthless pressure.

Transferred to a jewellrey or a sculptural situation, the ‘can’ is
sealed shut when the solder flows and fills the last possible gap
between the inside and the outside. The object will then cool to
room temperature and there will be a difference of pressure between
the inside and the outside. If the walls of the object are thicker
than the 0.3mm slab-sided tin can then they will remain relatively
un-distorted…well maybe some surfaces will bow in slightly
depending on the strength of the material.

If the can/jewellery/sculpture is later re-heated to soldering
temperature, the pressure on the inside will then rise up till it
equals the pressure on the outside just as it did when it was sealed
shut in the first place. There will be no excess pressure on the
inside upon re-heating…UNLESS…a tiny lil bit of water got inside
while you wern’t looking!

Steam is another beast altogether, it will power a locomotive, and
it blows things sky-high if it can’t get out.

Alastair

``````There will be no excess pressure on the inside upon
re-heating...UNLESS...a tiny lil bit of water got inside while you
wern't looking!
``````

Yes, but the only way that tiny bit of water could have gotten
inside is by being sucked in during cooling (when quenched) or
otherwise gotten in through some pores or tiny pinholes, such as
might occur if, during cooling and solidification of the solder, the
lowering inside pressure at the last minute sucks in a trace of the
solder creating a pinhole. However it happens, if there is some way
water got in, then it also stands to reason that the item is no
longer hermetically sealed, so internal pressure will have equalized
while cool. And further, if that can happen, then during subsequent
heating, excess pressure could escape, unless that original pinhole
(or whatever) became sufficiently and strongly enough blocked, as to
prevent that happening. Flux likely won’t do it, since as the item
heats, the flux melts, and liquid wouldn’t prevent air escaping.
Dried chemicals, such as pickle that had gotten inside and then dried
out, however, might indeed block/clog that sort of tiny pore, and
under that situation, pressure could increase inside the item. While
larger or exceptionally thin walled shapes might burst, in my own
experience, I’ve found that usually if that is the case, either
nothing much happens at all, or as it heats, the internal pressure
slightly bulges the item until some small break occurs, the clog
clears, or another gap opens up enough to let air escape, usually at
solder seams. While this can be damaging to the piece, I’ve never
seen one actually explode from such a scenario. This isn’t to say
something cannot blow up, but I believe it’s rare. The main examples
I’ve seen of a piece of metal blowing up on heating is with
shot/casting grain, usually shot I’ve poured or someone else has
poured, by pouring molten metal into water. If the temperature of
this is off, it’s possible to create shots that fully enclose a small
air space containing a bit of the water it was poured into. And those
little puppies most definatly do blow up pretty violently when you
try to melt your shot for casting, sometimes distributing a fair
amount of the metal you were melting in your curcible, around the
casting area…

Peter

Hi Richard,

``````What is the gauge of the metal of the large object?
``````

You can see all dimensions in original post at
Air holes for soldering - Jewelry Discussion - Ganoksin Orchid Jewelry Forum Community for Jewelers and Metalsmiths.

``````......how did you solder 5 closed objects onto a tube referred
to....
``````

Didn’t do it yet…Looking for Orchidian input before I
do…:-)…

Regarding a number of your points, let me sum up by saying: The
thread is about allowing air to escape from closed shapes so they
will not explode–nothing to do with pickle, since pickle cannot
enter a completely closed form…:-)… The air issue arises the
moment a shape closes e.g., some shapes on the tube are likely to
seal before others even if you are soldering them on all in the same
heating, which means you have to continue heating closed forms (in
order to close the unclosed forms). Obviously the issue arises even
more seriously if you solder each of the five shapes on separately,
or if the complex object will later be heated again for other

Hi Dan,

Fascinated to hear you use such large holes!!! Do you do this
because you had problems with smaller ones? Or just to be safe?

If this is a one time piece that you are afraid to damage, you have
to go larger and them cold close them latter (another discussion) if
needed.

The holes will be in the parts of the tube which are covered by the
closed forms (to allow the air in the closed forms to escape via the
tube), so they won’t show anyway. As I wrote in the initial post,
the final ‘closing’ of the tube will be screwed in place i.e., no
soldering.

Janet in Jerusalem