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3D printing problems

3D printing for mold making in ceramics requires determination and skill. And a memory for the many problematic techniques.

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Poor plaster release from 3D printed mug handle case molds

My objective was to continue skipping the making of a rubber case mold and 3D print them directly. Since 3D printed surfaces naturally part well from plaster and the artifacts, although visible, do not show on the final fired pieces, I even wanted to do this whole process without any sanding or oiling. However, despite printing a dozen or more variations, carefully controlling plaster/water ratios and waiting/mixing the recommended time periods, few good plaster molds were extracted without corner-breaking. Even painting the inner surface, oiling over it and beveling corners did resolve this issues. It seems that a combination of the printing artifacts, sharp corners, the handle perpendicular (because of the oval cross-section) and the inside negative shape all enabled the plaster to get a very firm grip on the PLA print. Although I could have resorted to a heat gun to soften the PLA material enough to pull it away I relented and decided to switch to making a block mold (for rubber) rather than a case mold (for plaster).

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.

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 of printed support out past the edge - that part has to be cut away with a sharp blade knife to enable mating with the other pieces.

Assorted problems with 3D printing PLA molds

I am 3D printing a block mold - rubber will be poured into it to make a case mold for beer.bottles. It is an amazing process but there are still issues to deal with:
-Stringing (top left). This usually happens when the nozzle is running too hot. This new batch of filament needs a slightly lower temperature, so I adjusted from 215 to 207.
-Size constraints: This is too big to print as one mold so it has to be done in multiple sections (two mains, two end-caps). Pieces fit precisely and can be glued or taped.
-Experience shows where glue, tape or special brackets (e.g. corners lower left) are needed.
-Special tools must be made (lower left is a clip-insertion tool).
-Corner lifting: Happens mid-print (the large thin pads on the lower right are to prevent that).
-Pressure bowing: The stabilizer bars spanning the two mid-pieces (lower left) and the triangular lip (upper right) keep that edge straight despite pressure from the liquid rubber inside.

Warping of PLA under heat of plaster set

When cutting a larger object into multiple pieces it is important to have an assembly plan.
In this case I have glued at the pieces together (and filled and sanded the joins) and plan to fill the two on the left with plaster to make them rigid.
I should have 3D printed inserts to cap these ends instead. The printer can produce a very precise fit and they can be super-glued in.

Belt and suspenders base for 3D printed mold

This assembly is the bottom half of a 3D printed 0.8mm wall thickness PLA mold. Until now I have super glued a thin disk onto the bottom, but a plaster pour again woke me up to how much outward pressure the heavy slurry exerts on molds tasked to contain it - the glue failed! This time I am doing a "belt and suspenders" solution. This bottom disk is much thicker and stronger and it is removable. These paper clamps hold it onto the flange and are recessed so the whole thing can sit flat-side down on the table.

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