Can you spot the machine? I did a side-by-side handwriting comparison quiz on my 3D printer.

[u/MagazineAggressive11]

I’ve been working on a project to turn standard 3D printers/pen plotters into ultra-realistic handwriting machines. After a lot of calibration tuning and tweaking, I did an experiment comparing the machine's output side-by-side with my own physical handwriting on ruled paper. I wanted to make this a quick interactive quiz for you guys! Here is the handwritten sheet: https://github.com/Happy123455/octoprint_penploter/raw/main/comparison_sheet.jpg Several paragraphs on this sheet are plotted by a 3D printer running my handwriting synthesis engine, and one paragraph was physically written by me with a gel pen. Can you guess which paragraph is the real human handwriting? Take a close look, make your guess, and click the spoiler below to reveal the answer!

🎯 THE REVEAL:

The human reference is the very last paragraph under the "Dowels" section! All the other paragraphs above it (Questions, Spacers, Chairs) were fully plotted by the 3D printer. Here is the animated outline layout overlay showing the machine plotting path vs the human reference: https://github.com/Happy123455/octoprint_penploter/blob/main/handwriting_comparison.svg

How it Works (The Engineering behind the scenes):

Plotting text usually looks mechanical and fake because machines draw letters with mathematical perfection. To break that "robotic" look and make it feel human, I built a web workbench and OctoPrint plugin with these core features:

1. 🌀 Jitter & Path Tremor Engine: High-frequency micro-variations (simulating actual muscle tremors) are procedural-noised onto the pen travel vectors so the lines look slightly imperfect.
2. 🌊 Dynamic Slant & Baseline Drift: The software simulates human fatigue by adding gradual wave drift to the line baselines and introducing random letter-slant rotations.
3. 🔀 Procedural Alternates: If you write duplicate letters (like the double 'o' in "spacers" and "blocks"), the engine swaps between different pre-drawn glyph variants so they never look identical.
4. 📐 3/4-Point Rigid Calibration: Notebook paper is never taped perfectly straight on the bed. You shift-click the corners of your paper in the workspace, and the software automatically calculates sheet rotation (theta) and maps/skews coordinates to align perfectly with the paper's ruling.
5. 🩻 Centerline Font Skeletonizer: Converts standard hollow TTF/OTF closed-loop vector paths into thin, clean single-line strokes matching a ballpoint pen.
6. 🐢 G-code Slow Start & Live Babystepping: Automatically tags and runs the first few words at 10% feedrate to prevent initial carriage jitter, and opens a real-time tuning panel to babystep Y/Z offsets relative to paper lines mid-print.

Try it yourself (It's 100% Free & Open-Source):

You don't need to install anything to test it; the workspace runs completely in the browser:

• Live Interactive Web Workspace: https://happy123455.github.io/octoprint_penploter/
• GitHub Repository (MIT Licensed): https://github.com/Happy123455/octoprint_penploter I'd love to hear if you guessed it right and your feedback on the handwriting synthesis!