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How to fabricate an hollow donut?


#1

This is a dumb question, but can someone help me? I want to
fabricate a hollow 3D donut shape. The only way I can think of to
make it is to take tubing, fill it with sand or something, and bend
it around a mandrel then join the ends. Does anyone else have a
better way to do this?

Mary Ferrulli Barker
Technical Business Consultant
Addision Avenue Federal Credit Union


#2

Mary,

If you are talking about hand fabrication and not casting you might
want to try making two pieces out of half round wire and then
soldering the two together to create the 3D doughnut.

Greg DeMark
If You Like Antique, Vintage or Custom Jewelry
www.demarkjewelry.com


#3

Depending on the scale and detail of your piece…

Make two halves in whatever manner is suitable. Formed sheet or
castings. Solder together like a clamshell. Its a good idea to have
at least a tiny drilled hole to vent water vapor that might have been
inside the halves. You would have great latitude in dimension and
shape. Use material thick enough not to warp too much when heated.

Bent tubing will work, the result will be uniform dimensions close
to what the tubing started as. There’s a limit to how small a radius
a tube will bend to without major deformation.

You might think of it in terms of inner vs outer dimensions. If you
want a truly donut shape(small hole, fat body), clamshelling is the
way to go. If its more like a bicycle tire, tubing will give more
uniformity and symmetry.

Good luck


#4

Mary,

There are a few considerations that go along with your donut. First
is does the donut have to be viewed from all sides? If not you may be
able to cast the donut instead of fabrication, by making a model that
is about 80% of the donuts hight and an open back to support the
core. If full view is needed then fabrication is very possible, but
the difficulty will depend on the measurements you want. I think the
two critical numbers are the diameter of the donut hole and the
diameter of the donut cross section (the size tubing you would make
the donut from). The smaller the donut hole the more difficult the
job. The larger the cross section the more difficult the job. Just
were the numbers intersect I can’t say. Maybe someone has already
done this. The other option I think, is to view the horizontal cross
section of the donut, and either fabricate or cast the two halves for
soldering.

Dan
Daniel Culver


#5
I want to fabricate a hollow 3D donut shape. 

I think if I were doing this, I would make a die out of masonite or
plexi, with a straight-sided (cylindrical) hole and a cylinder in the
middle, and form the metal (Argentium, if silver) with the hydraulic
press, then solder two pieces together. Does that make sense? With a
little experimentation, it should be fairly easy to make nice domed
half-donuts this way.

Noel


#6

Hi Mary;

This is a dumb question, but can someone help me? I want to
fabricate a hollow 3D donut shape. 

This is certainly not a dumb question. It’s an interesting problem,
but you don’t quite give us enough for me to suggest
which of the following solutions might be more appropriate.

First, the tubing solution might work, but bending tubing is an art
in itself. You are somewhat limited by the diameter of the donut in
relation to the tubing diameter and metal wall thickness. For
example, if the donut were to be 2 inches in diameter, the tubing 1/4
inch, and the wall thickness around 20 gauge, you could probably do
it with a coil type tube bender that slips over the tubing. But you’d
be near the limit of feasibility for this approach. You’d bend it in
a slight spiral, going past a complete circle, then cut both where
they overlap and re-align the ends and solder (leaving a pin hole
somewhere for expanding gases to escape. As the donut required
becomes smaller, the diameter tighter, the wall thickness greater,
you reach a point where it will take too much force for the tube
support of the bending coil to keep it from collapsing, or it gets
simply to hard to bend it.

If the donut were, say, 2 inches in diameter, the cross section of
it an inch, and the wall thickness 20-22 gauge, your best approach
would be to carve half in the donut in wax and use that to make
devcon dies and resort to a hydraulic press. With the press, you
wouldn’t actually need Devcon dies, you could probably use dies sawn
out of plywood and faced with masonite (see masonite die forming
below). The dies would be a thick plate, faced with masonite, with a
circle cut out. This would be glued down to a piece of plywood, and a
plywood “plug” the diamter of the donut’s hole, also masonite faced,
would be centered in the larger hole and glued down. A soft durometer
rubber pad would push it down into this die. Much thicker metal and
this wouldn’t work well. But this could form two halves, which could
then be soldered together, again, the pin hole for expanding gases.

If the donut were much smaller, say, half an inch, with a cross
section of 1/4 inch, the simplest approach would be to carve a wax
donut, allowing a little extra thickness at the “equator” and saw it
in half, then hollow it out, cast the halves and solder together.

Now, the hard way(s)… If you’ve got good hammer technique, you
could form two halves in pitch by chasing and repousse, and better
yet (a way I’ve used to make these sort of things) is a technique
called “masonite die forming”. There isn’t room here to go into that
except to say it uses the aforementioned plywood and masonite die
system, but the metal is clamped down to the die and free form
hammered down into the cavity. Another variation would be to use
anticlastic raising techniques, again, it takes some metalsmithing
skills, but it can be done (yep, done it myself).

If the donut were really large, say, as big as a Jell-O mold, you
would probably be best off sub-contracting it to someone who did
metal spinning, but I doubt that’s what you’re after.

So, whereas all these approaches are a lot of fun, really, what you
can resort to will depend on your skill level and your equipment. So
finally, can you tell us more about the dimensions of this proposed
donut? Diameter of the donut, diameter of the cross section,
thickness of the metal wall, etc? And what metal are you using,
silver, gold, brass? Give me that and I’ll point you in
the right direction. That said, it wouldn’t surprise me if there is
someone else here who can cut to the chase better than I can.

David L. Huffman


#7

If you have access to a hydraulic press, How about carving the
negaative of half a donut into delrin, and pressing it into urethane?
OR: make a circular matrix die, with a solid circle in the middle.
Each of these methods would make half a donut (or bagel). You would
then solder the two halves together. (I find it best to use paste
solder on the inside for that job.)

Cynthia Eid
http://www.cynthiaeid.com


#8

Hi Mary,

how about forming it in two sides then soldering? e.g. making a
circular die with a raised centre, pressing two shapes, filing edges
true, soldering

cheers, Christine in Sth Australia


#9

Mary,

Depending on the size that you need, there are some suppliers that
sell coiled tubing that is typically the size used for bangle
bracelets. If you are looking for a different size you could make a
positive mold in wax of 1/2 the donut shape and then make a negative
mold of that in epoxy-steel and use that mold in a die-forming press
to form the piece in sheet metal and solder two pieces together to
form your donut.

Joel

Joel Schwalb
www.schwalbstudio.com


#10

Dear Mary,

Two other ways to fabricate a hollow donut shape.

  1. Carve a wax to be the donut shape you want. Cut the wax in half
    along the side of the donut, and then hollow out the inside of each
    half, cast them and solder the two sides back together.

  2. Make a circular matrix die out of 1/2 inch (25mm) thick Plexiglas
    or Lexan plastic. Out of the same plastic make a plug that will be the
    center of your donut. Set up the die with the central plug in a
    hydraulic press, put a sheet of metal over the die, urethane pads on
    top of the metal sheet, then pump up the hydraulic press to create one
    side of the donut. Repeat to make the other side. Saw the donut forms
    out of the metal sheets and solder them together.

Hope this helps,

Nanz Aalund
Associate Editor / Art Jewelry magazine
21027 Crossroads Circle / Waukesha WI 53187-1612
262.796.8776 ext.228


#11

Were I given this job, I’d make a sphere out of two circles and then
deform it to the shape of a donut. Some details, after making the
sphere place the piece in a steel dapping block and with a relatively
small dapping punch start deforming the sphere (imagine that your
putting two dents at the opposite poles of the sphere). Continue
until the deformed areas meet in the center of the sphere, annealing
as necessary. Secure a flat punch (one that is the same diameter as
the inside diameter of the hole in the donut) in a vice, place the
proto-donut on that punch and with an identically sized punch in
opposition, hammer the center together. Cut out the center of the
sphere carefully and solder the inside edges together with a lower
melting point solder than what was used to form the sphere. Be sure
to stress relieve the object before you solder the inside seam or you
may have a catastrophic failure.

What a fun mental exercise. Good luck.

Larry


#12

This reminds me of a school project. We took a sheet (about 3 inches
wide), soldered the ends, making a large ring, then using a
sinusodal stake we formed the metal into an antisynclastic form, then
taken care to properly anneal the metal closed the form over (as this
streches the metal is will work harden quickly). The name torund
(sp?) comes to mind as a descriptor of a roman bracelet if my memory
serves.

K. David Woolley

It bothered me that I didn’t check my post [ABOVE] properly before
sending it out and mispoke, anticlastic is the term I was groping
for. I only put out a revision since I finally found the title of the
book I was trying to remember:

Form Emphasis For Metalsmith By Heikki Seppa

I do believe it has a section on the form you are looking to make,
if anyone has a copy on hand and could check that would be cool.

Kindest,
K. David Woolley
Fredericton, NB
Diversiform Metal Art & Jewellery


#13
There's a limit to how small a radius a tube will bend to without
major deformation.

To bend a very tight radius in tubing it mush be filled with
something to support it. This is a key problem in making musical
instruments such as trumpets and trombones where, for example, brass
tubing of 1/2" diameter and only 25 thou wall thickness has to be
bent into a ‘U’ shape with only 1/2" between the two ends. The old,
traditional way was to fill the tube with lead, bend it and then
melt the lead out and pickle away any residue. However, the modern
way is to plug one end of the tube and then fill it with water. this
is then stood upright in a freezer overnight or, at least, until the
water is completely frozen, and it can then be bent in a normal tube
bender without risk of buckling. When it is bent, of course, the ice
simply melts and the water runs out leaving the tube clean without
having to pickle in acid. Other substances have been used for
filling tubes to bend such as sugar, sand etc. but none is as neat
and easy as water ice.

Ian
Ian W. Wright
Sheffield UK


#14

Make two domes. Pierce the hole out of the bottom of each. Solder
together. Cut a rectangular piece of sheet that is the height of the
donut hole (width) and the circumference of the hole length. Form
into a circle (like a bezel). Fit it into the donut hole and solder.
Finish.

Lather. Rinse. Repeat. :wink:

Brian Corll
Brian Corll, Inc.
1002 East Simpson Street
Mechanicsburg, PA 17055


#15

Thank you, Project: Hollow Form - Clasps from etch sterling to match the etched beads! Now I just need to add a tube set gem and that project is completed. Off to the studio!

Deb
deb@gemrapture.ca


#16

Hi,

i suggest metal forming technique

  • read this book: Creative Metal Forming by Betty Helen Longhi and Cynthia Eid
    (i just did and it is fabulous!)

-cut a strip
-solder seam closed
-create anticlastic (outside seam) or synclastic (inside seam) curve until Magic U is achieved

  • close the U into an O by hammering against mandrel correctly

that is just a short explanation, the book tells all!

so funny! i just did an exercise on open seam circular spiculum!

julie


#17

Thanks, Julie, that is a great book!

My donuts are precut etched sheet, knocked the centers out for bead caps which leave the resulting donut.

My question is how to get the center hole to dome in the opposite direction without loosing the domed shape of the exterior dome? Do I need to place the domed donut in a form to hold the shape while I dap the interior donut?

Deb


#18

Hi,

ah. I see!..hmmm…

I have no idea, but I will think out loud here!

generally speaking, you could continue the shaping by:

1: hammer/ emboss it down into an appropriately shaped depression (and located on the wood in the right place! edge, corner, etc)

2: form it over an appropriately shaped stake/ round dapping punch…

3: use a thin mandrel thru the hole and hammer down in the appropriate spot on the washer to have the hammer and mandrel work in concert to curve the metal into a U shape…

4: a combination of all three…

I think that a depression can get the curve started, the round punch can further the curve, and once a magic U is achieved, the mandrel could help further curve…

in a perfect world, you might have a succession of depressions, or stakes, or hammer head sizes, to progress thru…

I am just starting to play with the tools that I have and see where I can get with them…

think about what shape and curves you need, to get you where you want to go…ie: the humps on a sinosoidal stake, hammer faces as stakes, round dapping punches, etc…you can modify steel and wood too,

then again, there is always the hydraulic press too! that is on my wish list, along with a Leica Microscope!

I made a few depressions using a #8/13mm and #9/10mm straight gouge…

I did just buy a few #9 spoon gouges from Woodcraft…and I find that using a punch to dap down the wood fibers after shaping the depression with the gouge will harden the shape up a bit…

with that said, I would think you could get half a donut easier than closing the washer into a complete donut(?)…

just my musings…

Julie


#19

hi again!

i probably should have inquired:

what is diameter of washer?
what is diameter of hole?

:hugs:

julie


#20

Thanks Julie, I will start on that list!

Deb

Nine](http://www.9folders.com/)