|Monthly Tech-Tip |
This project is being done to demonstrate the amazing power that 3D printing brings to ceramic slip casting. It is now possible to quickly draw 3D objects on a computer, 3D print mold-molds and have working plaster test molds within a couple of days. The more pieces a mold needs to have the better this system works. It is interesting to note the precision that is possible using this process - and that achieving that precision can be done by simple trial-and-error recreation of test molds. Additionally, a potter can create partial or small-scale molds to prototype and then have full-size rubber masters made at a 3D printing service provider.
Ceramic beer bottles were made historically. They are a very difficult shape for jiggering, needing to be done in two parts and joined. Thus, many companies even had teams of potters making them by hand. Slip casting using traditional mold-making techniques was never practical compared to the metal molds used in glass forming. That being said, ceramic bottles have some important advantages over glass - these include decoration and customization options, practicality for potters to make, flexibility to retool size and shapes, flexibility in glazes and colors and options for stamping and embossing. Ceramic glazes, especially stoneware glazes, also have the potential to be more durable. So it is easy to see why we are excited at how easy it now is for potters to take advantage of the ceramic process in ways industry could not.
This is Fusion 360. The profile was drawn and various measurements parameterized. That means the measurements were given names (e.g. body_diameter, thickness). This makes it possible to change aspects of the geometry of this shape by just editing the parameters. If you are experienced in 3D CAD you will be able to see this drawing is actually beginner-level, I have not fully defined it. And, I have not done so in such a way that its height and width can be changed while maintaining the shape. I should also have placed the center of the lip at the origin. Further, it does not need to be hollow, it should be a solid body.
Coming soon: Drawing your objects in 3D is the most difficult step in leveraging 3D printing for your production. We will create it first in Fusion 360 and print it on a Prusa printer (using Prusa Slicer). Then we will do the same process using Blender and a different slicer and printer.
These stopper mechanisms are a commodity item, millions are made and a wide range of bottles work with them. They are easy to fine oneline and go by a variety of names (e.g. "Grolsch style flip top stoppers", "Swingtop Grolsch style bottle cages", "Porcelain swing top cap").
To predict bottle neck diameter at the holes I measured the gap on all of the ones I have and got an average to work from. Then I 3D printed several iterations of the neck and settled on one that enabled being able to snap on the metal fitting without stretching it. That exercise hit a dead end when I realized the wire assembly is bendable and can be adjusted for size - the clamping mechanism is intended to be squeezed into place on a narrower neck.
To make a master mold tall enough I had to 3D print a four-piece PLA mold-mold (because of the limitations in the size of my 3D printer). That created an awkward-to-use mold that left a horizontal seam (in addition to the vertical ones). It became clear that I was ahead of myself, it is more important to get the neck geometry correct first (so the stopper fits and works properly). The drawing needed to be redone to define the shoulder and body height parametrically, the last step would thus be to set the correct height and have the final larger mold-molds printed at a service provider.
This is another example of the flexibility potters have compared to manufacturers. These 3D-printed gizmos are stuck onto this beer bottle mold using the casting slip. Dipping their flat surfaces and attaching them takes seconds. Another feature of this mold for potters only: There are no notches (the halves were poured into disposable 3D printed PLA masters - and mate perfectly). Using the rubber band to hold them together was not ideal because realignment of the halves damages the square inside edges. By using this method the mold halves can be aligned accurately. The 3D printed pouring spout is likewise attached using the slip (it also helps hold the mold halves together).
PLA is the most common filament used in consumer 3D printers. It has a very low melting point so even hot water can soften it. The PLA printed mold-mold (lower right) has vertical sides and it would be pretty well impossible to remove the plaster mold from it without significant damage to the corners. Making these two mold halves was a testament to how accurate 3D printers are nowadays, the pieces mate precisely. Notice there are no notches, I feel they are not needed (lining up the outer edges perfectly positions the pieces).
This commercial bottle is 25cm high. The wire mechanism is attached very firmly. I can measure it to derive the required dimensions of the mold. My preferred clay is M370, M340 or a black version of them.
The dark one is M370 with 10% added raw umber. The other is M370. Both are glazed using GA6-B Alberta Slip amber transparent. This glaze is the best functional super gloss recipe we have. The wood-grain texture is the artifact of 3D-printing the mold-mold, they are not detectable to the touch.
In Fusion 360 I sliced off the top of the bottle and formed a small box around it to be able to quickly 3D print a test mold. Two of these mold-molds printed in about 3 hours, the next morning I cast the plaster molds. After drying on top of a firing kiln overnight they were ready to use the next day. Making a hole in the middle of the wire mounts was easy at the leather hard stage. The wire is 2.8mm dia, a 9/64 drill bit is 3.5mm. Simply twisting it to create a hole in the center of the pads takes seconds. Firing these to cone 6 will enable testing the fit for the swing assembly.
The centre one is M370 + 10% raw umber - leather hard out of mold. The other two are fired at cone 6. The 9/64" holes made at leather hard are big enough for the wire but too snug a fit, the hole is breaking (as you can see on the right). The pad also needs to be bigger, 8x8 mm will be the next test. The hole being 21mm down from the rim is about right, the mechanism is locking well.
|By Tony Hansen|
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