Neck Molds & Other Stuff

Rev. ... 05 February 2003, -02-06, 05-06, -07-20, -08-29, -09-22
2004-07-05, 2005-01-13, -01-14, -01-30, 2006-03-21,
2008-1-06, -01-31, 2010-01-17, -02-19, -03-21 (rermovals)

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Intro - I began exploring foundry work (melting metals) as a method of making tools for glass work and for making shapes to blow glass into (see also Forging work.)

[Mark wanted to make an optic - my reply is:] If you are doing a one shot, you could buy investment, cast a core out of the investment, carve the core to the shape you want, patching and repairing it as errors are made, cover the core with wax and cut the wax to the outer shape you want, with sprues etc., cover the wax with investment in a tube shaped metal surround, heat to remove the wax, further heat to dry the investment, and pour. (Maybe pour a few small samples first to see how dry to get it, etc.) When done you would break/wash the investment out - it softens in water, unlike plaster/silica mix.
If you wanted the chance to make more than one, then it would be best to carve either 1/4 section of the inside (positive) or the core (negative) in plaster or wood, to make a negative in plaster. On this negative, you could cast/pour 4 wax (casting wax, not paraffin, etc.) mold sections that you would assemble to make a lost wax original, add sprues, etc., pour investment all over, set, heat to remove wax, dry, pour, etc. as above. 2001-10-09

NEW LEARNING 2001-06 - I finally used the shellac I bought some time ago to coat the outside of both a plaster and a sanded wood mold shape. It makes removal of the mold shape much easier. I also did some casting with shapes cut from pieces of Styrofoam, not removing them before pouring the metal. Cast aluminum puffer headA major stink, but a nice form. In both cases, I was casting in the sand mentioned below. I have added some more oil and I strain it through screening to remove bits of metal and occasional burned sand. The results, along with more pounding of the sand, are much smoother castings.

This is the second cast puffer head, much smoother than the first. Aluminum is tapped for 1/4" water pipe (about 1/2" OD) and the fitting shown allows the copper tubing for blowing. A reducing fitting 1/4" to 1/8" allows screwing it onto a standard air valve for a shop blower.


CASTING - (Originally from Hot Glass Bits 41) - I have been teaching myself casting, borrowing generously from books, web sites and suppliers. My purpose is to be able to cast aluminum parts for tools to manipulate glass and brass or bronze pieces into which I might blow glass - goblet stems and feet, cages, etc. The aluminum I am using is from melting soda pop cans, most of which I drink - far too many as I see the accumulation. The brass, which hasn't been used much so far, is from some old brass letters and keys around the Store. My experiments this summer (1999) have been aimed at making a tool for shaping the necks of bottles so standard caps will fit with the additional goal of trying to put threads on for standard screw on caps. I have already learned that the latter is not going to be easy. In exploring for materials, I rather quickly settled in on Swest, a national supplier to the jewelry industry that is located here in Dallas. I gradually learned various things through books and looking at the supplies offered. I learned most of all that what I wanted to do was a rather awkward size, being big for jewelry related stuff and small for foundry casting sort of stuff.

Previously, I had made an expedition to Ft. Worth and from a foundry supply company (all of them seeming to be over there) gotten a bag of premixed foundry sand (it has a chemical that forms a binding agent with the very fine sand when an astonishingly small amount of motor oil is added.) It is interesting stuff that I have not yet worked with very much. [I learned later that I was not making the sand nearly damp enough for most purposes - besides the oil, it needs water to the point it clings together. 2003-02-05]

From Swest (and with their advice), I bought a box of investment, a modest supply of green casting wax, an alcohol lamp, and several tools.


Investment looks like plaster, is much less complicated to mix and stands the heat of molten metal. It is not waterproof and in fact is removed from the molds and molded material by soaking in water. Investment is not strong enough to stand alone (I learned in one failure) when molten metal is added and must be contained inside a sleeve. Swest sells stainless steel sleeves with rubber bases and I bought one, but the sizes are limited and the prices go up rapidly. I happened across a length of 3" (nominal) thin wall conduit at the used metal yard and bought it for several purposes one of which is making these sleeves. I am thinking of getting some 4" conduit. [2001-10-09 I did, in fact, track down a source - Dealers Electric, a chain - and buy a 10' piece, about $20, which was cut apart to get it in my rental car. I have cut a chunk off for foundry and will cut a slice for drilling glass, putting silicone sealant on the lower edge to hold fluid. 2003-09-14 Did this latter, didn't work very well.  Have made a number of rings of various heights and diameters 2, 3, 4" dia, 1, 2, 3, 4, 6 tall, plus sheet metal wrapped in cylinder and held by stainless steel band (hose) clamps, for the largest.]]

[CUTTING large tubing so it has square ends: Wrap a piece of typing paper around the tubing until the ends (nearly) meet, line up the edge, tape it in place. Use a marking pen around the edge. Cut the tube with a hacksaw, saber saw or reciprocating saw.  Image below as part of mold ends.]

When using a proper SS sleeve, a rubber end cup both seals it and supplies a pattern for pouring the metal because the wax is built on the ring of the cup. I build my pieces to sit with flow tubes (vents and risers) pointed up and put a layer of thick investment in first after wrapping the bottom opening of the sleeve with aluminum foil and sitting it on a plate. Then somewhat thinner investment is poured around the wax model as I support it in place. Before pouring the metal, I carve out a funnel shape at the end of the risers, usually just before the final heating after wax melt out. [2003-09-14  I have changed methods after having the wax float up one too many times.  I now make the risers and pouring funnel all the same height and turn the wax upside down, using silicone adhesive to glue it to the aluminum foil - I use heavy duty.  This keeps the wax from floating and makes pouring the investment less of a two step process.]

These mentions of wax make it obvious that I am using the lost wax method of casting. Getting the wax model that is to be lost is a multi-step process which I will go though without trying to cover everything in the books on casting. The overwhelming advantage of lost wax is that all the considerations of pattern casting - drafting the edges to remove the pattern, designing the pattern to avoid or relieve undercuts, getting the pattern out - can be set aside (mostly.) The disadvantage is that a new model must be made for every product, which may involve a master mold and time reworking the resulting model. But that can be an advantage, as the wax is nice for hands-on working with heated tools. (Basics)


These are the steps, with added comments, in making the molds for the bottle neck former I am fooling with now. The design (evolved while working on the wax models, I will admit) is a three part unit to be mounted on a 1/2" tubular shaft: a center post to form the inside of the bottle opening and support the neck as two blocks shaped to fit the neck ridges are closed with a plier action to form the glass. The blocks have enough aluminum to carry the heat (I hope [yup, when tested]) of the glass, which is way above the melting point of aluminum. The center post is now two cylinders in line, a larger short core inside the neck and a rod of smaller diameter but longer, supporting the center core.

The original model was made by taking plasticine clay (artists' and children's non-softening modeling clay), forming a roughly shaped rod and fitting it in the bottle being used as a model. This soft clay model was then used to make a plaster mold in the halves of a small plastic bottle using standard clay mold techniques. (i.e. support the model so the plaster will come to the centerline of the model, pour plaster and set; treat the surface with English soap as a release, add the other half mold, cover the rest of the model, set and unmold.)

After the model was made and used to make one aluminum casting, it became obvious that the core was too thick and too long. The original plaster mold was used to make additional wax models by adding plastic clay to reduce the diameter and length where needed. The final form is a rod 3/8" diameter about 2" long attached to a cylinder about 3/4" in diameter by 1" long which is rounded opposite the rod to more easily fit in the bottle neck and has a lip opposite (around the rod) to form the inside of the lip. (B)



The two halves of the body of the former started by taking the same plastic bottle halves used above and making a plaster cylinder 2" in diameter and 2" long. Originally the plan was to use this to make the pattern of the outside of the shell which would be filled with hot wax into which would be pushed a prepared investment core. Latex rubber molding compound was used to make molds of several bottle necks and several cores were poured. (C) Plaster and investment mold castings, with latex molds
When the first attempt was made to carry out this idea, problems that would be obvious to anyone with experience with plaster molding and which are mentioned in the books, became obvious to me: There was no way to accurately align the core, so making a good cut for a split was impossible, so the fit on the glass would be uneven. Further, getting the cylinder out of the unsplit plaster mold was very difficult. Despite this, the whole process was carried through once, just for practice (and hope it might work.) A wax impression of the cylinder was made with an investment core pushed in place with enough hanging out to lock the core into the surrounding investment. The wax was used to make a lost wax mold (see more below), the wax was melted out, and a casting was attempted. For a first try, the results were okay as castings. However, the core broke free on one and was badly misaligned on the other and attempts to saw the cylinders cleanly in halves were absurd. First molds and casting attempts
Having the cast cylinders in hand made it clear that it would be hard to make a unit that could be handled easily, so the mold was used to make a new plaster cylinder model that was tapered to allow easier and closer attachment of the spring supports. This model was further carved to shape and was used to make a more traditional split mold. A small cardboard box was taped up and lined with thin aluminum foil. The model was treated with separator and plaster was added to the box and the model pushed into the top. When set, the box was built up, the surfaces treated with release and the top of the mold poured. This gave a basic working mold. (A) Small molds with aluminum castings

Investment and plaster working information once here, moved to Goblet Casting

These are the most recent efforts. The mounted blocks and core are aluminum, shown carefully mounted on a handle that holds the core with a set bolt.  The spring bars are held with small hose clamps.  The casting is brass, shown with vents and pouring funnel still in place.  They have been sawn off and the blocks will be tapped 10-32 to use the same handle.  Both of these will make a neck like a glass Coke bottle. I am working on a mold for one with threads off a plastic soda bottle. 2003-07-20 Neck mold mounted and newer casting
[Recently I observed an old bottle forming tool and the sides that formed the neck shape were actually flat across the profile which it immediately seemed to me was better because it would force the turning glass into shape - the design above doesn't work well because it has no flow control - it wants to just push. 2010-02-19]


In the mad rush before going off to the workshop with Fritz Dreisbach, I was trying to get some successful small animal heads molded for pushing into the glass.  I botched several, but these two sort of came out.  The cat head to the left and the dog to the right were modeled in plasticine clay and a latex mold was built from those.  Casting wax was poured in the mold and a pre-cast wax stem attached to the back.  I was doing several things in parallel and didn't really decide on a handle until after these were cast so the far end was ground to 3/8" diameter to fit in the 1/4" NPT pipe all thread to the right, with a set bolt to hold them.  Only the dog (dubbed a wolf) got used.   The inset needs to be really chilled (with blown air to keep the details. ) Crudely cast cat and dog head molds for pushing into glass.
The picture shows two versions of paperweight attempts and a bowl, pressed in the bottom and then backed with a cookie, with only the nose and ears showing somewhat..2003-07-20 Picture of glass from Dreisbach workshop with pressed dog head


Fritz brought and used several stamps with attached handles, including a large and small lion head.  The worker puts a very hot bit on the piece and presses a mold into the hot glass.  When I got home, I decided to extend using the casting to make a few stamps.  I used molds I already had made up in some form.  The three images below include the results.

Cast molds for decorations - the making process

These three castings were made with investment inserts.  A rubber mold, such as the one in the right hand image, was used.  Liquid investment was poured in and allowed to set.  The two round items were made with models that had been carefully trimmed, the rectangular with by leaving the overflow.  I have had problems with an insert falling free inside the mold.  These trimmed ones were carved away on the back so the mold material would key/lock in, but it dawned on me I would get a much better lock by not trimming and using the flange of the overflow to lock the insert.
In each case, the insert was glued with 100% silicone adhesive (tub caulk) to a piece of heavy duty aluminum foil.  The two round ones had the foil shaped around a small bottle before gluing.  The rectangular one had the foil folded up around the overflow.  When the adhesive was set, melted wax was poured over the insert to make the image block.  When this was set, the foil was peeled off.
Since I had decided on 3/8" for handle mounts, I had drilled cast plaster for 3/8" and after soaking in water, poured wax to make pre-formed rods, which I heat welded to the center back of the image block.  I also had pre-formed funnel-shaped pouring forms and less nicely formed vents, which were welded to the corners.  Taped and wired invested mold Each wax model was trimmed so all the risers were level and was again glued to heavy foil to keep it from floating in the investment.  A steel ring like those on the right was placed around the piece, the foil folded up and investment poured in and rapped to removed air bubbles. [At right is an invested plaque showing the pouring funnel and vent rising above the investment.  In this case, two rings were needed for height so they were taped with metal tape and then wired because the aluminum tape disintegrates at the highest pre-heat of the investment.]
 After heating and pouring metal, the investment was washed off and the castings removed.  The saw cuts removing the funnel and vents can be seen on the leftmost brass round piece above.  They will be ground smooth.  In the same image can be seen the back of the rectangular unit with the funnel at back, three vents, and center stem with overflow. 
The center shows the faces of the image blocks.  They are a butterfly, a triangular ornament, and a profile of a Labrador retriever.  The butterfly was a button sold at a craft shop and the investment insert was worked slightly to enhance the lines that were color on the original.  The ornament was a mold for candle decorations etc.  The lab was modeled in clay originally. 2003-07-20

Mold cup cast of alumium with dog head insertAt right is a cast aluminum cup about 2.5" across with 0.25" walls and floor.  Originally three were cast together, this being the best, one failing for lack of metal and one with a distorted floor. The three were stacked and supported about 0.5" apart and invested.  They were made by melting wax floating on hot water and letting it cool to about 100F, cutting while still warm and curving to fit.  The bottom was cast buy placing aluminum foil around the ring and pouring wax in.  The rough dog head was cast using the rubber mold above to make a wax positive that was then invested.  The bottom will be drilled and the head tapped to hold it in place.  The cup will be used for color pickup and for impressing the dog head into a shaped piece of glass. 2003-09-25



Cast brass from September activities.These four brass items were cast in September 2003.  The large initials in the lower left have been hanging around for some time and were made by directly carving in investment, putting a ring around it, and pouring wax.  Added investment with a larger ring made an open face mold which was poured into.
  The initials above, which have a stem on the back were made by carving into Sculpy clay and then pushing a ring down into the clay, which produced a raised curved surface.  Wax was poured into the ring and removed and stem, pouring funnel and riser were added to the wax.
   The heart was made for casting some cane core.  The heart was shaped in Sculpy and a ring put around it and wax poured in.  The Sculpy was then cleaned out.  This is NOT a good technique as the cleaning was most tedious.  Sculpy is baked to set it and the hot wax formed a gooey bond with the clay.  Plasticine modeling clay would have worked better.  The casting needs work to eliminate under cuts.
  The fourth casting pair in the insert is the threaded neck mold. 2003-09-22

Mold preparation for small moldsThe picture to right shows the steps I use in making flat molds for sulphides and glass.  I bought the wooden disks at Hobby Lobby or Michaels.  Using either plastic clay or Sculpey, I build up the image, like the profile of Washington taken from the coin, often while riding or waiting for the bus, with the detail work being done at a table. See sample tools above.  Then thin layers of molding latex are painted on, making a flange on the surface.  Avoid the temptation to put on a thick layer, which takes much, much longer to set than many thin layers, even if cleaning the brush is a nuisance.
  Before the clay model is removed, I make an aluminum foil cup around the bottom of a glass and set the disk in it so that I can put plaster of Paris neatly over the disk.  The purpose of the plaster is to support the latex mold when wax or investment is poured in.  The shell mold looks like the lower left on top of its support.  To the lower right is the support for the head (Lincoln) above it.
  The mold can the used with casting wax or investment.  If the wax is used, the result is covered with investment, the wax melted and burned out, and the hole filled with glass or metal, as making the dog and cat heads above.  If investment is used, then it is encased in wax in shape of metal, which is then further invested to allow casting a mold like those shown above. 2004-07-05

Head mold (both sides) and supportHaving worked on the clay face for the bottle mold this picture illustrates the pieces and two sides of the latex mold.  Through a curious optical illusion, the interior mold seems to bulge out at us.  The plaster keeps the latex from distorting under the weight of investment and heat of melted wax. The lower image shows the outside and also shows how the latex turns white when kept moist - in this case from the plaster backing.  It is weaker in this condition, but dries out and strengthens again, turning a uniform amber.  Notice that not enough plaster was piled on, so there is a hole where it was thin over the nose. 2005-05-01.

Untrimmed castings of stamps These are the untrimmed castings of two projects.  The herringbone pattern on the right is two halves of a leaf crimp used for putting the vein pattern into (usually green) glass, the tip of which is then pulled to make a leaf shape.  Each has a flat tab on the back for bolting to tweezers or pliers.
The shape on the left is less clear, but the lower is a zipper pull and the upper is the zipper track.  Each has a post on the back for mounting in piece of pipe for a handle.  The intension is to lay a moderately thick trail of glass on a vessel with a blob at the end.  The pull stamp pressed into the blob will leave that image standing, then the track stamp will be used several times to make a track out from the pull.  A fair amount of handwork will have to be done on the pull stamp   2005-01-14

Rough casting of 3 items: zipper & initialsThis is the rough casting of three items, 2 of which survived further work. The white material is investment which completely encased the molding, most of which was removed with water soak and pressure, the remainder will take fine pick tools.  This was the first casting where I used copper wire pins to locate the pre-cast investment cores.  Apparently, despite this step, the core on the lower item shifted to allow a thin layer of brass to surround the core.
On the left a side view of the casting shows the rods cast in place for the handle, which connect to the vent.  The brass was poured in the center bottom funnel shape (image is upside down from pouring position)
On the right, we face the working portion of the stamps.  The top and smallest is my initials MF.  Below this is another zipper track stamp, which broke horizontally on disassembly*. And below is the largest, a complete casting of the pull stamp with the thin shell over the opening partly peeled back.
* When I started to pour, the metal was clearly too cool, so I stopped, prayed, put the crucible back in the foundry and the mold into a 1000F oven.  After several minutes, the metal was fully hot, and the pour continued.  The first metal can be detected in both the track and pull but the track broke while the pull casting wobbles - I may tap and bolt it.  I am learning, gradually. 2005-01-30



These are two versions of tappers made for breaking thick glass.  The upper one was cast in lead in plaster from a modeling clay original. It was drilled for the handle after casting.

The lower one was cast by building up casting wax on a stick by dipping in molten wax and smoothing.  The stick hole was used for mounting a small hole venting for investment to enter the hold.  A poor porous casting, however the black line is not a crack but a guide to a smooth part for tapping.  The plaster has been used to make a wax for an invested lost wax casting with proper spruing. 2008-01-06

Tapper head - clay model, plaster mold, wax for investmentTop center is the clay original, then the two part plaster mold used for casting the lead at above, and wax cast from mold, sprued for better brass casting, not yet cast. 2008-01-12

Rough casting of tapper aboveThis is the rough casting from the wax made by dipping and poured from above the actual rather than into a sprue.  The tube to the left is acting as a vent from the side, so the top of the ball and stem are porous.


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