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Medalta Ball Pitcher Slip Casting Mold via 3D Printing

This project will follow progress as I create a master mold for use at Medalta Potteries in Medicine Hat. For information on the general track I will take check the beer bottle and mug mold project (linked below). Various aspects of this shape are quite challenging (e.g the handle, the shape of the lip, the angled foot). I will post pictures as I repeat cycles, version numbering where appropriate. When it is all working well I will remove all but the last successful version.

Related Information

Medalta Ball Pitcher

Here is an example of one that was for sale on Ebay. The inset bottom will be a challenge, for version 1 we will likely settle for a flat bottom.

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.

Warping during a large print - one solution is multiple pieces

I am attempting to 3D print a shell for making a rubber block mold (the base of a Medalta ball pitcher). This is almost at the limit of what will fit on the print-bed. It would take 30 hours. But at about 10 hours it did this: All four outer corners warped upwards. I have a larger printer but it will do the same thing! What is the solution? Cut it up into smaller pieces and print each of them at the best orientation (bottom right), this saves significant printing time and achieves better quality. For this piece, the inside surface on the center section is most important, printing it upright with printed support took about 4 hours. All the other pieces print in about 1 hour each. Tape (either masking or MicroPore) can be used effectively to hold everything together for super-gluing or epoxy. Much of the tape can be left in place during the pour. The rubber form has thin 1cm walls, but these are supported by side-rails when plaster is poured.

Medalta small ball pitcher first 3D print of block mold

I cut it in two horizontally in the slicer software printing the top part upside down. This minimizes the amount of printed support that needs to be printed (thus greatly reducing print time). This was done on my Prusa MK4, the two halves mate perfectly. These two took about 6 hours to print. The support easily releases (I use a needle nose pliers).

Printed mold halves taped, railed, ready to fill

Filling the printed form, from the back, with plaster makes it rigid for the next step, pouring a case mold. The flimsiness of the printed shell is actually an advantage, the weight of the plaster pushes the mating surfaces down onto the table. The rails impose perfectly square corners and flat sides. I will pour the plaster just to the top of the printed part (not the top of the rails).

The plaster-filled block mold negatve

The two parts mate perfectly, the slight seam is easy to remove from the plaster negative that will be poured against this. Although polygons are visible on the inner side, they will not show on glazed pieces. Notice there is no provision for matches or spare, the reason will be clear later in the process.

Ready to pour a block mold

I have sanded the rings on the inside top and bottom - just smooth enough the release won't be too difficult (on the plaster block mold and will be able to smooth them more effectively). I also applied some Murphys Oil Soap on the those sections. Now it is just a matter of filling this with plaster.

Two block molds are ready for casting working molds

At this stage any imperfections in the 3D print are easily removed from the plaster surface.

Block molds railed ready to pour working molds

The plaster block molds have been oiled using Murphys Oil Soap. I printed the side rails to fit (by measuring the lengths and widths precisely and dividing them by two).1.7kg of plaster was enough to fill them both.

First working mold ready for pouring

Two halves of my first test working mold are ready. I'll put them in our lab dehyrator for 6 hours at 150F to dry them out over night. I'll cast the first pieces tomorrow using our new recipe for M370 Casting.

First ball pitcher casts successful. Sort of.

The top has not yet been trimmed. We first tried casting this using a fast-casting clay body, but the process was very quick and the pitcher dried so fast that by the time I got it out of the mold it was too brittle to cut properly with a fettling knife. This is a second cast, using M370C. It casts about three times slower (3-hour mold cycle time) but there are no issues with cutting the top to shape. Well, actually there are - it is very difficult to get the shape right, a template is needed There is an issue with the handle also - it is too close to the body and too thin and delicate.

Version 4 Ball Pitcher 3D printed block mold

This project continues to demonstrate that multiple redesign, test cycles are a fact of life when making a new shape. 3D printing makes this so much easier. Here are the changes from v3:
-This time I am not going to back fill with plaster. I have heftier side rails that should hold things firmly in place.
-The rim is now cast in into final shape.
-The includes a distinct footring, this will enable easier cleanup of glaze on the foot and a cleaner edge line.
-The handle is thicker and looks a little further from the body (to enable getting my fingers in there).
-I am using natches this time, the two 9mm holes will mount embeds (the retainer and embed are shown beside the holes) - they will position flush in the case mold (I will propagate the embeds into the working mold also).
-I am casting it upside down, positioning the spout between the lower handle join and the foot ring. We will drain for ten seconds then plug the hole using a plaster insert made to fit snug. Remaining slip inside will refill the hole and even build the wall a little thicker there (increasing wall strength by the lower handle join).

Ball pitcher v.4 case molds cast

We are just using pottery plaster for now. Notice the embeds for the natches. This time I did not backfill the 3D prints, that is better - because they are flexible they were much easier to remove from the set plaster. The side rails help keep them firmly in place and scotch tape on the backs was sufficient to keep them lined up at the join. These prints have a wall thickness of only 0.8mm. I did not need to use a parting agent nor did I do any smoothing on the 3D prints (although some cleanup on the plaster case mold will be done). Next step: A working mold, version 4.

A method to make a two-part slip casting mold in one pour

This is part of a project to create a new mold. I have to make various iterations to arrive at a final design where rubber will be used to make the case mold. But until then I will 3D print the case mold directly. Here are some features that make this super cool:
-The center section is the jug being cast (two pour spouts will be glued on). It is hollow and will be split horizontally in the slicer so the two halves can be printed with open side up and then glued together (with the aid of printed inner hoops to align them).
-The mold seams, where the two halves mate, is printed as a 0.4mm membrane connected to the model and running vertically down its center.
-The membrane has 9.4mm holes for the insertion of standard mold natch pairs. During plaster pour the membrane will flex somewhat, this will be a benefit to aligning the halves.
-The outer shell halves have no angles steeper than 45 degrees and thus print without printed supports. The flanges were drawn using our rotation technique (see link below).
-The round flat base will be glued onto the bottom disk.
-Any rough surface sections of the model (printed on top of support), will be coated with a fluid epoxy to smooth them.
-A separate handle mold will be made.

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 (especially if a surface is down-facing and on top of printed support). 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!

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 Printing an entire one-off case mold in one piece

This 3D printed shell encloses an entire two-piece mold for v 5.0 Medalta Potteries ball pitcher - all that is needed is to fill it with plaster and peel off the PLA casing after it sets. We are still in the development stages so the fact that this will only produce one mold is fine. The membrane across the center is where the two mold halves mate (it also holds the inner model in place). The membrane has holes where natch-pairs can be mated for embedding into the plaster mold. The spare (shown lower right) will be rotated 90 degrees, it has a slot that fits snuggly over the membrane to hold it in place. The handle is being done separately. This was printed on a consumer 3D printer with standard PLA filament.

Extreme handle fitting: A Medalta v.5 ball pitcher

This handle mold is for v.5 of our 3D mold-making (and discovery) project for the ball pitcher. The process to make the 3D drawing is quite simple: Cut it out of the model (top left), draw and extrude side walls (top right) and slice off and remove the pointy parts (a step-by-step video coming soon). Bottom left: A ready-to-use mold. Notice how it fits perfectly onto the side of the pitcher form (bottom right). Because of the good fit, attaching these is just a matter of using some casting slip as the glue. Casting this handle separately affords multiple benefits: It simplifies making the mold of the pitcher itself, of extracting pieces after casting and it produces a more professional-looking product (without holes inside where the handles join). And, handles can be stockpiled in a damp box, ready to use when needed.

Inbound Photo Links

The Prusa MK4 3D printer is worth the upgrade from MK3

Links

URLs	https://medalta.org/ Medalta in the historic clay district site
URLs	https://tonyhansen.com/medalta/index.php Medalta, Hycroft and Sunburst Pottery Catalogs from the early and middle 1900s Sunburst: 1964, 1966, 1971, 1974 Hycroft: 1967 Medalta: 1924, 1939, 1947, 1953
URLs	http://medalta.pastperfectonline.com Medalta Collections Database at PastPerfect - Search for the word "drawing" to see the mechanical drawings for hundreds of pieces
Projects	Beer Bottle Master Mold via 3D Printing A project that took several years of failures and blind allies and is finally coming together - so much simpler than expected!
Projects	Coffee Mug Slip Casting Mold via 3D Printing A potter can now use AI, 3D CAD, 3D printing and custom clay bodies to slip-cast beautiful quality stoneware pottery mugs. It is efficient and practical.
Projects	Nursery plant pot mold via 3D printing
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.
Glossary	3D Design 3D Design software is used to create dimensionally accurate objects by sketching 2D geometry and transforming it using tools to rotate, extrude, sweep, etc. The software generates the polygon surface.
Typecodes	Mold making using 3D printing An ordinary consumer 3D printer has many exciting possibilities for making many types of molds, it is a place where people having both artistic and mechanical abilities can get a double the dopamine!

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