Skip to content

3D Printing

From OpenSCAD to the Classroom Desk: 84mm Fraction Towers, Logarithmic Prime Blocks, and Unit-Tested Books

Whenever we tell someone we are manufacturing a new calculator alongside 3D-printed math blocks and printed textbooks, the natural question is: "In a world with smartphones and AI, why does the world need another calculator?"

Because even in the age of AI, students still need to know how to think mathematically. Handing a child an AI chatbot—or a standard school calculator where they type nested parentheses (12 + 8) / (5 - 1) = into a black box—hides every intermediate step of reasoning. By contrast, on a stack-based RPN calculator, students learn operator-precedence parsing themselves because they must break expressions down in the right order of operations to enter them onto the stack, seeing every intermediate result step by step. And unlike CAS (Computer Algebra System) calculators—which are banned on the SAT, ACT, IB, UIL, and college math exams—our calculator is purposefully designed to be allowed in testing situations (zero CAS symbolic manipulation, zero QWERTY keyboard, and zero wireless radios on the hardware).

Our goal with the StackCalc Ecosystem is to make every step of mathematical reasoning visible and physical, connecting 3D-printed classroom manipulatives (manufactured in-house and on Slant3D), unit-test-verified reference books, and our SC-6 / SC-32 calculators.

The TPU Button Video Is a Design Review, Not a Slow-Motion Test

A simulation is much more useful when it makes a design argument visible. In a static CAD view, a TPU key, a faceplate opening, and a switch location can all look compatible. The difficult part happens between those still images: a keycap drops, tilts toward a wall, transfers motion through the web, and either reaches the switch or spends its travel rubbing somewhere it should not.

That is why we made a cutaway video of the StackCalc TPU membrane. It is a short design-review tool built from the same membrane and faceplate STL geometry used for the prototype, not a claim that the unpopulated calculator has already survived a life test. The RP2350 board is in fabrication; the video lets us inspect the mechanical questions now and gives the first board session specific cases to repeat.

We Pressed One TPU Key 280 Ways Before the PCB Arrived

A calculator key rarely gets pressed straight down in the middle. A thumb catches an edge. A finger comes in from the side. A child presses a corner. The first question for our TPU membrane was not “does it move?” It was “which bad presses leave enough room for the key to reach the switch without scraping the faceplate?”

The StackCalc PCB is in fabrication, so the printed calculator is not yet a powered keypad. We used the interval to put numbers around the geometry that will meet the board: the printed faceplate aperture, the TPU web, the keycap stem, and the proposed tactile-switch interface. That produced a 280-condition press sweep and the plot below.

From an Origami Box to a Puzzle Stand

Shipping support is usually dead weight: it protects a device for one trip and then disappears into a bin. We wanted the StackCalc packaging support to keep earning its space on a desk or shelf. That changed the design question from “how do we protect a calculator?” to “what can protect it, organize the kit, and become useful after unboxing?”

The first answer was an origami fold. The current answer is a printed puzzle stand: four dovetail-connected corner pieces form an upright shelf stand, while a separate strut becomes a low desktop typing support. The printed pieces and the package envelope are still being refined together, but the change already made the whole product feel more connected—from the first opened box to the way the calculator lives between uses.

A printed StackCalc prototype docked in the shelf-stand assembly.

A Tool-Free Calculator Built Around a Sliding Assembly

“Tool-free” is easy to write on a feature list and hard to make useful in a printed enclosure. The test is not whether an assembly has no screws; it is whether a person can insert, retain, inspect, and later release the parts without turning every opening into a breakage risk.

The current StackCalc assembly is an unpowered, four-part mechanical prototype: a tapered chassis, unified faceplate, TPU membrane, and snap-retained top cap. Its RP2350 KiCad board is in fabrication, but no assembled board has been installed, so this remains a mechanical design lesson rather than an electronics assembly claim.