2019 Jiggering-Casting Project of Medalta 66 Mug

In 2019 I learned 3D design software and how to use 3D printing. Many things I have made using this I either could not, or would not, have otherwise done. It is incredible! And knowing about these enables me to "tool up" much more easily to mass produce a product.

The best accomplishment: Printing the master jigger molds and template and handle-casting molds for a scaled-up Medalta 1966 coffee mug. It took a year to go from concept to the first production mug. Perhaps the single biggest factor was learning how to use engineering consultants online (at Upwork.com). That helped me getting over the biggest obstacle: Learning to use 3D design (or solid modelling) software. I was lucky, by the second consultant I tried I "struck gold". Right at the start he talked me out of using Blender and into using Fusion 360. I needed his help about 20 times through the year. He repeatedly made videos showing exactly how he did things. He always drew things "parametrically", in such a way that I could adjust drawings. At the start I gave him a cross-section drawing, that I made using 2D software, that was all he needed, everything he later did was based on that. Most times I needed only open the file he sent me and print it.

The exciting events that frequented each stage of this adventure were the 'adrenaline' that kept me going. The first was being able to rotate his 3D drawing in my copy of Fusion 360, that was an eye-opener. Then (after months of struggle building my first 3D printer), printing a prototype that I could hold in my hand! Other landmark including seeing those incredible masters for the handle molds printing. Another exciting thing was seeing how fast 3D printing evolved in just that year. And how easy it was to adjust drawings and reprint as I learned, at each stage, what did not work.

After scaling it up by 10% (to allow for drying and fired shrinkage), I went through a series of failed ideas on how to print the mold for the master model and then the forms for the block molds for the jigger and handle molds. Other projects I was doing at the same generated ideas that led to eventual success. I ended up printing the mug model mold in two pieces and gluing them together. And the shell mold to fit around it needed to be printing in two pieces and glued also (it splits vertically for easy removal, being help together using simple paper clamps). By the time I got to doing these I had my second 3D printer, it produced much better quality. I was amazed how smooth a surface it could print, plaster poured against can be smoothed in seconds with just a metal rib. My 3D printer nozzle layers down 0.45mm wide paths, so I doubled that and printed 0.9mm thick walls. These were rigid enough that no deformation occurred when full of plaster.

Surprisingly, the jigger molds fit perfectly into the aluminum cuphead the first time! But then the template tip did not clear the far side of the mold as I brought the jigger arm downward! Then magic happened. I printed a new narrow template that just went down the side
but not across the bottom (which, by the way, had such a clean edge that it was not even necessary to sand it). Then I slip-cast a mug in a jigger mold using a 3D printed pouring spout (that I had developed for another project), this spout made it possible for the clay to extend well up from the top of the mold. Then I finished the cast mug, while still soft, by jiggering just the wall and lip. Voila, that lip looked like one on a thrown mug. The mug dropped out of the mold easily a while later and gluing on one of the cast handles was quick.

Then something else magic happened: The template only needed to go down the side-wall part way (the cast surface was smooth and perfect). It also became evident that I did not actually need the jigger arm. Why? Because it was easy to just hold the template in my hand, no, it was better! So no jigger arm was needed! In fact, with a heavy banding wheel and a jig, it would not even be necessary to have the jiggering wheel itself, just a quick spin and press of the template and each mug lip can be finished!

I have found that this process has a number of benefits:
-I can cast, finish and attach handles for a batch of mugs in a couple of hours. There is no need to cover them for trimming later, they are done.
-The cast mugs do not need special drying (no cover or drying chamber), casting clay has such low shrinkage nothing cracks.
-The casting process enables using every scrap of clay.
-Once the molds are made and you have a pail of slurry, no other special equipment is needed (you can make the actual pieces in your kitchen if you want).
-Wall thickness is totally in your control, thick or thin.

Related Information

Hand-tooling a mug model vs. 3D-printing a mold to cast it

I am creating molds for a 2019 casting-jiggering project to reproduce heavy stoneware mugs manufactured here 50 years ago. I have a profile drawing I want to match (upper left). The solid plaster model on the left was my first attempt at manual tooling. The metal template was time-consuming to hand-make, its contour was difficult-to-match to the drawing and the plaster surface turned out rough and difficult-to-smooth. To make the plaster model on the right I printed a shell (using my 3D printer), poured the plaster in, extracted it after set and then smoothed it on the wheel using a metal rib and trimming tool. It matches the drawing perfectly and the round is very true. 3D-printing is revolutionary for this type of thing! The drawings: I hired someone on Upwork.com to make them for me (using Fusion 360). The shell-mold (to cast the model) on the upper right: I printed that too, in two pieces.

The incredible utility of 3D printing master handle molds

These molds are 3D-printed from PLA filament. They are part of my 2019 year-long casting-jiggering project. A quick soaping, 164g water, 236g plaster and a fifteen minute set produced this plaster mold. It takes time to learn how to soap the masters properly to get optimum quality, but these molds seem to work well regardless. The two halves mate with a tiny amount of play, but it is easy to line them up perfectly (the play actually enables lateral movement that aids in releasing the handle). It is actually easier to cast handles solid rather than pour the slip out, they can be ready to apply in an hour after pouring. The ease of making these molds puts slip casting within much easier reach for potters and small companies.

3D-Printed master mold, handle mold made in it, first cast

The halves fit together well. Even with a thick handle like this, the mold splits for me in less than an hour when casting solid (and in half an hour when cast hollow). The cast handle is very sturdy and easy to cut and glue on to leather-hard mugs. As a parting-agent I use Murphy's Oil Soap on the 3D-printed PLA mold, this makes it fairly easy to extract the freshly-cast plaster molds (the sidewalls have a draft of about 5 degrees). The PLA mold is very durable so it is practical to use the end of a knife to get soap residue out of the recesses (when cleaning). If I do not remove the soap bubbles sufficiently before pouring in the plaster, corners are poor quality (so the mold produces a more visible seam on the cast handles). Notwithstanding that, the open plaster mold shown produces excellent quality handles.

3D-Printed rail to cast working plaster jigger molds

The grey outer rail on the left was printed in two parts and glued together (at the shoulder). Its vertical split enables me to open it a little. The center model of the outside contour of the mug (on a two-step base) was made by casting the plaster inside another two-piece 3D-printed form I had made (we had to use a heat-gun and scissors to get the PLA printed form off of that plaster). I smoothed the surface on the wheel using a metal rib and trimming tool. Then I stretched a rubber band around the first step at the bottom (because the rail was a little lose-fitting). Now it fits perfectly and clamps tightly in place. To cast a jigger mold it is just a matter of soaping the plaster model and the inside of the rail and pouring in a mix of 1300 pottery plaster and 900 water.

Slip has been poured into the mug and handle molds

Notice the 3D printed pouring spout. And that the mug mold fits into a jigger wheel cuphead (for finishing the lip and truing the inside vertical wall).

3D render for a jiggering template

Print this using PLA filament and it will be plenty strong enough to use (even if not printed solid). The knife-edge will print very precise and smooth, giving a good profile. After making several of these I discovered that I could hold them in-hand to finish a mug I had already slip cast in a jigger mold (a jigger arm was not even needed). The profile contour was easy to copy from my drawing of the mug itself. This template is fairly narrow, this was needed so the backside cleared the rim of the spinning mold as the jigger arm is lowered. But now that I use it in-hand, I could increase that dimension so it finishes right across the base.

My potter's wheel with aluminum cup-head and jigger mold inserted

The cup-head was lathed from a block of aluminum and it attaches to the shaft the same as a regular wheel-head. Plaster molds simply drop in and sit on their shoulder. The shoulder is the only point-of-contact, this prevents chattering while the mold spins when under pressure. I am using these molds for a casting-jiggering process (or just casting). For example, I can cast a mug in the mold, then pour out the slip, wait a few minutes and then, as the wheel spins, finish the rim and inside sure using a 3D-printed template/rib. I do not actually use the jigger arm, it is easier just to hold the template in hand. I can finish the rims on any round pieces made in these molds.

3D-Printing the Medalta 66 prototype mug

First, we did the 3D drawing in Fusion 360. It took 12 hours on this inexpensive build-it-yourself printer! Notice the supports it prints for the handle, these break away after it is done. Of course the surface is not smooth enough to use as a model for mold-making. But to be able to hold it to judge size, wall thickness, handle feel and shape is very valuable. All other drawings we made (for molds, templates, spouts, etc) were based on this starting point.

3D Printed prototype beside first dried piece

On the earlier pieces that I made (like this one) I had the walls too thin to be able to effectively round the lip and true-up the inside using the jigger template.

Cone 10R mugs made with new casting-jiggering process

Very exciting! The easiest batch of mugs I have ever made, no wheel throwing or trimming. These are made from two casting recipes I am working on to match the fired appearance and glaze compatibility of Plainsman H550 and H440 (buff and iron red burning bodies). This is how many you have to make to learn some of the finer points of the process.

Jigger/Cast mugs 2019

Made from H550 Casting and firing at cone 10R. One of the advantages of this method is to make pieces, not just thicker and heavier as these are, but consistently so.

Final cast-jiggered cone 6 mug beside original 3D-printed mock-up

This is a product of a casting-jiggering project I did in 2019 to recreate a 1960s Medalta Potteries mug. The first step was drawing a profile in 2D (using Adobe Illustrator) and then working with a Fusion 360 freelancer at Upwork.com to create a quality 3D drawing. 3D printing this mock-up was possible after that, using my favorite 3D slicer, Simplify 3D. The mug was drawn "parametrically", that is, measurements and geometric relationships were built-in such that changing contours and the size preserved the original design. The first production mug, made about a year later, is on the right. Molds were scaled up 10% from this mockup size so that final pieces would be this size, however the firing shrinkage of the clay turned out to be about 12%.

Fusion 360, my choice for 3D modelling in ceramics

Intimidation by the complexity of this type of software is the biggest obstacle you will face to learning 3D design (for 3D-printing). Fusion 360 is the new mission of AutoDesk, the leader in CAD software for 30 years, bringing much of the power of their industrial strength Inventor product into the hands of everyone! Fusion 360 has a lot of advantages. It is a standard. There is a simple learning curve via their Tinkercad.com, videos on Youtube, easy online help and many freelancers to hire (at Upwork.com). It is free to qualifying users (teachers, students or people who earn less that $100k/yr), the fact that software of this kind of power and utility is actually available to anyone who wants to try it is amazing. Fusion 360 (and other 3D design products) cannot run 3D printers (3D slicers do that). Fusion 360 is very demanding on the processor and graphics hardware of your computer, typical laptops are not powerful enough.

Links

Glossary	3D-Printing Standard 3D printing technology (not printing with clay itself) is very useful to potters and ceramic industry in making objects that assist and enable production.
Glossary	Casting-Jiggering A process in ceramic production where items are slip-cast first and then finished using a jigger wheel.
Glossary	3D Printer Standard 3D printers (not clay 3D printers) are incredibly useful in ceramic production and design, bringing difficult processes within reach of potters and hobbyists.
Glossary	Upwork Using the services of online freelancers connects potters and small ceramic producers to expert engineering talent at low cost.
Glossary	Restaurant Ware If you are a potter and want to make restaurant ware, read this. Many of the things you already think you know will mislead you in this type of venture.
Glossary	Jiggering Jiggering is a process of forming pottery that employs a spinning plaster mold and a tapered template to press soft clay or porcelain against it.
Glossary	Slip Casting A method of forming ceramics. A deflocculated (low water content) slurry is poured into absorbent plaster molds. As it sits in the mold, usually 10+ minutes, a layer builds against the mold walls. When thick enough the mold is drained.
Projects	Project to Document a Shimpo Jiggering Attachment Make your own jiggering attachment for your potter's wheel. Here are the plans and lots of help to get you going with molds and techniques.

By Tony Hansen
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