This mold-making technique I have wanted my whole life

I wanted an easy way to make molds for slipcasting handles that mate perfectly to any shape mug (or pitcher, teapot, etc). I want to pair cast with thrown or jiggered elements and join them using just slip (even when the clay is stiff). We have developed a flexible CAD design that puts 3D printing of case molds within the reach of almost anyone. It requires so little tooling it can be done in a kitchen using spoon mixing and a paper cup! These PLA shells, for example, print quickly to only 11 grams and they peel away from the plaster with a heat gun to give fine detail and perfect fit. Multiple cycles of redesign and print are practical to achieve just the right shape and fit. Cast handles can be produced in quantity and stored in a damp box, removing one of the biggest hassles in the production of handled ware. The feel of the handle is the first thing customers notice, even a hobbyist can now turn a "wet noodle" handle into something designed and utilitarian.

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Coming soon: Throw the teapot and slip-cast the lid

How would you like to be able to create a parametric CAD model of a teapot lid? Then 3D print a case mold and pour a multi-piece plaster working mold? Imagine easily making multiple-size one-off molds to accommodate any teapot you throw!

This is perfect for M370 or Polar Ice (both have throwing and casting versions). Or, how would you like to be able to formulate a casting slip having the same appearance and degree of maturity as the throwing body you use? More information coming soon (based on the L4807 casting body).

Next, imagine casting the handles and spouts also. Information on how to draw and print them also coming soon.

3D-printing plaster mold natches, spacers, clips and embeds

Plastic natches are cast into plaster molds to provide a durable and good-fitting interlock to ensure pieces line up perfectly. The traditional one familiar to most people is the 3/8" or 9.5 mm size (nipple diameter). Because of issues surrounding their use (not the least of which are price or even finding a supplier), we designed our own. Ours have several advantages:
-There is never an issue with supply, we make them.
-13.5mm holes in the case molds are all that is needed to adapt to these.
-3D printing case and block molds means we have to pour plaster and rubber into shells with planar mating surfaces downward, they must sit flat on the table. Clips with a very thin flange solve this, they hold the embeds inside in place.
-Casting an embed into a mold is more flexible since we can glue (or friction fit) a natch or a spacer inside.
-Since there are no natches protruding on the flat mating surfaces these can be sanded for better flatness and optimal fit.
Our drawing (right) shows the measurements we use. 3D printing is precise enough that the inside dimension of the embed is the same as the outside of the natch shoulder, yet the natch slides in perfectly (the same good fit happens with the clip and embed and the natch nipple and spacer).

CAD for 3D printing a mug handle block mold

This was done in Fusion 360.
1: A make a sketch of a box, around the handle, on the XY plane. Offset that outward by 1.2mm (my printer prints 0.4mm wide, three passes give good strength).
2: Extrude to create box 1: The base backward by 1mm and the sides forward by 20mm.
3: Use five sides of the box as cutting planes to slice it out of the mug.

At this point I could print this in PLA filament, pour plaster into and then use a hair drier to peel it off. But let’s make rubber molds instead.

4: Move the box-with-handle away from the mug. Pull the four sides out by 5mm to thicken them.
5 & 6: Create box 2 around the outside of it, as a new body, 1.2mm wider and taller, 1mm more frontward and 1mm less backward.
7: Use box 1 as a cutter to remove material from box 2 and then pull the outer 1.2mm sides 5mm backward.
8: Shell out the back side to 1.2 wall thickness and make two 9.4mm holes (to accommodate natch clips).

To make side 2 mirror-image a new body using the front or back as the reflexion plane. The back side is then filled with PMC-746 rubber to make the block mold. Plaster is poured into that to make each working mold.

Links

Media	Drawing a Mug Handle Mold in Fusion 360 Lilly will take you step-by-step through the process of drawing a shell mold that can be 3D printed and used to cast a plaster mold for slip casting perfect-fitting handles.

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