Custom-printed rib smooths this plaster surface

This is part of a test hybrid case mold for a Medalta Potteries ball pitcher. The bottom plate is 3D printed and the top form is solid plaster. Recessed holes in the back of the plate enable securely inserting screws into threaded anchors embedded into the back of the plaster form. The upper plaster surface has artifacts (stair-casing remnants) from the 3D printed shell used to cast it. While these could be sanded out, we find that a flexible metal rib works much better. Even better than that is this custom 3D printed rib that I made, the edges are sharp and precise. I designed it with contours to match the belly, neck and rim of this piece. Using this, it takes minutes to smooth out the surface.

Related Pictures

Hybrid plaster/3D printed PLA mold demo

It leverages the advantages of both materials

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The challenge: Create a 3D printed case mold that incorporates a plaster section just for the finished surface.
Top right: The secret is M3 brass threaded inserts in pyramid-shaped 3D-printed anchors (I have just pressed them into the 4.4mm dia, 10mm deep, -3 degree tapered holes using a soldering iron). These brass/plaster pyramids embed into the plaster to provide a threaded hole that M3 bolts can screw into.
Upper left: We made a cross-section CAD drawing of a three-piece demonstration mold (upper left). The top plate has holes for the M3 bolts, air escape and natch clips and recesses for clamps to hold a 3D shell, with flanges, in place (not shown).
Lower left: The anchors have been screwed onto the upper plate.
Center left: The plaster was poured, and over-filled, then the top plate, with anchors, pressed down on top of it. After set, the plate was unscrewed and removed.
Bottom right: The plaster section has been reattached and natch inserts and anchors put in place. The plaster was not sanded or prepared, this is a demo.

Medalta Ball Pitcher Mold v10

Using 3D prints and plaster to make a hybrid

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This is version 10 of my Medalta ball pitcher case mold. I am still determined that a standard 3D printer with PLA filament brings complicated molds within reach of almost any potter or hobbyist willing to learn 3D design. The project has evolved to become hybrid, using both plaster and 3D prints in the final mold. Two views of the PLA prints needed to pour a plaster half-model are shown at the top.
-Plaster is poured into A.
-I attach threaded anchors to the underside of the baseplate C (using bolts through the small inner holes), they hold the plate firmly in place on the plaster half-model.
-B is a spacer, it is clamped to the underside of C (and aligned using bushings in the holes), it is only used during the model pour.
-Bottom: A is on a perfectly flat and level surface. It was filled with plaster just to the rim and then the baseplate was placed on top of it (the spacer acting to correctly position it). More plaster was added and a few minutes after this it was scraped off flush.
After hardening the spacer can be removed, the mold peeled off using a heat gun, and the plaster surface finished and soaped. The 3D render also shows one of the side rails, D. It holds in place by a flange that wraps under and locks into the holes (the last version used magnets; this approach has several advantages over that).

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