The v2 ball pitcher is way too big to 3D print. What now?

This is a Medalta Potteries medium-sized ball pitcher block mold, version 2.0 - it has a more oval body shape. Upper left is the top section (actually, it is half of the top section, a base will fit on to create a three-piece working mold. There is to 3D print something this large in one piece in a consumer 3D printer. Even if it did it would require 50 hours of print time! Also, working surface quality is affected by the orientation of printing (by support impingement surface stair-stepping artifacts. Further, a large print would almost certainly warp and corner-lift during printing. Cutting it into four pieces and hollowing them individually (in the CAD software, lower right) solved all the problems. Each of the pieces is still quite large, taking 10+ hours to print. But they can each be hollowed individually and rotated to the optimum position for the best finished surface (and print speed). It is amazing how well these four pieces fitted together. This approach really paid off because I made a mistake - and I only needed to reprint one of the pieces!

Related Pictures

Large mold a testament to what 3D printing can do

This is a 3D-printed block mold of a medium-sized Medalta Potteries ball pitcher being prepared for filling with silicone rubber (to make a case mold for pouring working plaster molds). Although I used two different consumer 3D printers, a Prusa MK3 and MK4, the four pieces mate very well! I taped them together first and then welded them using an ultra-violet curing superglue from Home Depot (6 seconds to harden). The glue leaves a slight bump - that is not a problem - can be removed from final working molds. Notice I also made a 3D printed displacer (bottom inset) - I fill it with rocks as I fill the mold with PMC-746 rubber.

Ball pitcher mold ready to pour rubber. But how much rubber?

PMC-746 rubber is expensive - this is large and it will use a lot. The displacer (left) will reduce the pitcher walls to 1in thick (rather than a large solid piece of rubber). Following is how I calculated how much rubber is needed. First, I used Fusion 360 to generate a solid model of the upper part of a pitcher (this mold will forms that). I sent it to the slicer and it displays the volume in mm3 (as shown in the screenshot inset). To calculate the total volume of rubber needed I did this: Outer Box volume (250mm x 205mm x 107mm = 5484cm³) - Inner Box volume (231mm x 180mm x 96mm = 3991cm³) + Pitcher volume / 2 (1817cm³/2 = 908cm³) - Displacer volume (292cm³) = 2109cm³ + 10% error = ~2300cm³ PMC-746 has a specific gravity of 1.0 and the mix requires 2 parts yellow resin to 1 part blue hardener. Thus: 33.3% of 2300 = 765g blue 66.6% of 2300 = 1531g yellow.

3D mockup for 1940s Medalta Potteries ball pitcher

No molds have survived so we are going to start from scratch. We will use Fusion 360 and 3D prints in PLA to create a block mold to make a rubber case mold. Learning to draw this rewarded me with some new 3D drawing skills. The geometry of the lip is challenging. It appears the piece will need to be cast with a full top and the lip shape and pouring hole cut manually (as was done originally at Medalta Potteries). I will likely have to create a 3D-printed PLA template as a cutting guide to get the lip contour more correct and consistent than they were able to do. Although not on the original, we are going to include a foot ring for easier glazing and better stability during forming and firing.

Infill and support issues with 3D PLA prints

Top: The left one has a rectilinear fill, the right a square grid fill. Notice the fill on the left has buckled part way up - this piece is too tall for that type. While the grid fill on the right is far more stable, it is not as easily removed (although it can stay in place here).
Middle: The piece on the right printed in half the time because the only fill needed is at the bottom. The fill is rectilinear and easily removed - it affects the smoothness of the surfaces but they are not a finished ones so it does not matter. However that method is risky, notice the failed print on the lower right - upward pull of the flat section pulled it away. This happened twice more so I chalked up the one success to luck.
Bottom: Took about 16 hours. Like others, the grid support that printed out past the edge - that part has to be cut away with a sharp blade knife to enable mating with the other pieces.

Links

Glossary	Infill
Projects	Medalta Ball Pitcher Slip Casting Mold via 3D Printing A project to make a reproduction of a Medalta Potteries piece that was done during the 1940s. This is the smallest of the three sizes they made.

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