The slip-casting process is well adapted for producing non-functional ware, especially having thinner walls. However it does not do well for functional pieces that require thicker walls and contoured lips (heavier cast walls have less regular wall thickness). However these issues can be dealt with by adding a jiggering step to even out the wall and round and contour the lip.
Hand-tooling a mug model vs. 3D-printing and casting it
I am creating molds for a 2019 casting-jiggering project to reproduce heavy stoneware mugs made 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! That drawing: I hired someone on Upwork.com to make it for me (using Fusion 360). The shell-mold on the upper right: I printed it using my own 3D slicer and 3D printer.
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 shoulders. 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. A 3D-printed pour-spout is attached at the top and then slurry is poured in and allowed to build a thickness against the plaster wall. After the slurry is poured out I wait a few minutes and then finish the rim and rib the inside surface as the wheel spins (so I am not actually using the jigger arm).
A 3D-printed pour spout in place on the top of a mug mold
I prepare to attach these by simply touching them to the top of the slip (it is sticky and coats the underside evenly). Then it is just a matter of setting it in place and and it glues down in seconds. I make these a little larger diameter than the top of the opening (e.g. 2mm) in the plaster mold, producing a small overhang on the cast piece. During the time in the mold, the clay slurry creates a thickness against the plaster walls but also extends upward above the top of the mold (inside the spout). A while after pour-out I am able to make a cut and lift the spout away leaving an over-hang, over-height and thickness that all play to enable jiggering the rim to the exact contour I want.
3D-Printed shell to cast working plaster jigger molds
The grey outer shell mold on the left was printed in two parts and glued together (at the shoulder). It's 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). It smooth 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 shell was a little lose-fitting). Now the outer shell mold fits perfectly and clamps tightly in place. The cast a jigger mold it is just a matter of soaping the plaster model and the inside of the shell and pouring in a mix of 1300 pottery plaster and 900 water.
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