I have a problem making hollow silver hemispheres and wondered if
any of you good folks could give me any advice…
The pieces I am having difficulty with are for the push buttons on a
cases of antique pocket watches and they are raised from thin sheet
like a small, round-bottomed cup. I usually make them by pressing a
1/8" or 3/16" ball bearing into the sheet while it is supported by
polyurethane or polypropylene sheet in the large vice, but it always
takes several attempts to get a good one as the silver usually splits
around the domed end. I’m using sterling sheet of about 20 - 24 SWG
and I anneal it first and then again after pressing the ball about
half way in (I need the ball to go in full depth to get some
straight parallel sides). Any ideas would be very welcome as I have a
pile of failed attempts…
Ian, try annealed sheet in a thinner gauge; I should think that 26g
would be adequate. A dome of that small diameter should not require
great thickness for rigidity unless it is to be depressed with a
hammer.
It would be far easier if you had a steel dapping set with a dapping
block. They are available in a number of sizes. The dapping block has
a series of hemispherical depressions, usually starting at 1/8" up to
1". A set includes dapping punches that match the size of the
depressions. With this you can easily create hemispheres which then
can be soldered together to form a sphere. I think that if you search
the archives that there will be more complete A dapping
set with block with 14 different size depressions cost about $70 here
in the States. Feel free to contact me directly if you need more
Joel
Though it is possible to make hemispheres the way you describe, if
you want more consistent results and less splitting you really
should invest in a dapping block with dapping punches. The block
supports the disk much more consistently over the entirety of the
disk. Without this support you’re likely to tear the metal as you
hammer it to get the metal to “round up.” As well, since the block
is much harder than the plastic sheet you are using now, you
probably won’t have to forge it as hard. Good luck.
Ian, If the shape you want is a straight sided cylinder with a
half-sphere dome on the end, then the more direct way (and easier)
would be to start with a disc and use a doming block for the
half-sphere, then solder it onto the end of tubing.
The problem, I believe, is that while you are trying to sink the
ball bearing into the sheet, it is, in effect, achieving all its
depth by stretching the metal entirely. If you were to cut out a
circle first and then sink it into a rigid depression such as a
dapping block, the circle would stretch at the deepest part, but
also, achieve much of its form by the outermost circumference
actually being compressed into a smaller diameter. Half stretching,
half shrinking. Imagine the resistance to compressing at the
outermost circumference when it is attached to a sheet all the way
around its circumference. It has to pull away from the sheet as
well as compress. Much easier for it to just continue stretching at
the outermost bulge.
I assume you have access to a lathe as you are a watch maker. You
can make a simple punch and die to make a tube with a hemispherical
end like you describe very easily. I will send you a jpeg of the
punch and die and if you have any questions about it let me know
Attachment Removed
Jim Binnion
James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160
@James_Binnion
Member of the Better Business Bureau
The appendix of Alan Revere’s “professional goldsmithing” has the
formula for determining the size of disk needed to make a
hemisphere. It also comes with a caveat that off the top of my head
goes something like this: “The accuracy of this formula varies
depending on the technique of the goldsmith applying it.” This is
one of my favorite quotes!
Professional Goldsmithing : A Contemporary Guide to Traditional
Jewelry Techniques
~Alan Revere , George McLean , Barry Blau
$69.95
Media: Hardcover
Release data : January, 1991
Larry
Also on the top of the list of favorite quotes: “Proceed with
vigor!” Especially when it is said by a client with whom I’m working
on a meaty custom job.
Thanks to everyone who has replied to my query. As a couple of
people picked up on its not just the making of a hemisphere but
taking it a stage further to make a short hemispherical ended
cylinder (why couldn’t I think of those words before - dohhh!) so the
dapping block (which I already have) idea goes only so far. I think
the answer may be a custom punch and die set on the lines of a
drawing Jim Binnion kindly sent me privately so that will be my next
method to try.
One of the fascinations of the watch restorations I do - notice I
say restorations and not repairs - is that they are almost all on
pieces which are over 100 years old. I strive to use only the
materials and methods which were originally used to make them so that
the new parts harmonise well with the existing and I don’t introduce
any ‘foreign’ materials which may adversely affect either the
existing old materials or the value of the piece. This means that,
for every watch I work on, a greater or lesser degree of research is
needed to try to identify how particular bits would have been made
and what exact materials were used. Often this can go as far as
learning about social conditions at the time the piece was made,
where they may have affected the way processes were carried out ( for
instance on French pieces made around the time of the Revolution or
on all pieces when wars or civil unrest affected the supply of
certain materials and alternatives had to be found etc. ) and also
analysing tool marks on components to try to compare these with the
known machinery or hand tools of the day and decide how they were
made. As many of these watches have ornamented cases - repousse,
enamelled, jewelled etc.which need minor repair, the dividing line
between watchmaker and jeweller often becomes blurred and I may spend
days or weeks learning how to do a particular process before I
attempt a repair One such restoration I have ongoing at the moment
requires that I make a tube of polished ruby or sapphire less than
1mm long with an outside diameter of just under 0.5mm and a bore of
0.3mm. I will then have to cut away part of the wall and round over
and polish the cut edges. All the sizes have to be an exact match (to
about 2/1000mm) with the original part as it is crucial to the
working of the escapement. The watch this is for was made in France
in 1728 - no electricity, only oil lighting, no ‘engineering
industry’ to provide high-tech tools. Any ideas gratefully
received… especially how to drill the hole as I don’t have a 0.3mm
tube drill
I find it therapeutic to carry out this research and to try to
emulate the methods of the true ‘masters’ - why not give it a go
yourself… Turn off ALL your electrical equipment and bottled and
piped gases and, using only the hand tools and machinery you have
made or could have made with the available resources of the 17th or
18th century, make a small but decorative piece of jewellery such as
a jewelled locket or a small box with a closely fitted hinged and
decorated lid. I’m sure the results would be enlightening and it
would also engender an appreciation for the achievements of our
forebears.
Another way to make the piece you want is to first use your dapping
punch to make a hemisphere a slightly larger than you want for your
part. Then take a large hole draw plate where one of the
intermediate holes is as large as the outside diameter of the
cylinder section on the part you want to make. Then take a domed
punch that has a diameter that is the same as the inside diameter of
the cylinder and use the punch to push the hemisphere through
successively smaller holes till it is the correct outside diameter.
This may be how this type of part was made in earlier times
Jim Binnion
James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160
@James_Binnion
Member of the Better Business Bureau
To make the balls try inserting a thin plastic sheet, kitchen trash
bags are perfect, between the ball and sheet. Then press. Use a new
section of the bag for each one. Thicker stock will also help.
Ductility decreases significantly with small Si increases, so review
the chemistry reports (certs) before you buy and pick a low Si
material.
