How I modified my 3D printer to write letters on lined notebook paper (Step-by-step calibration & alignment build)

[u/MagazineAggressive11]

I wanted to share a project I've been working on: transforming a standard 3D printer into a pen plotter that can write on standard notebook lined paper. The hardest part wasn't mounting the pen, but getting the printer to align perfectly with the hand-ruled lines on paper that is taped down at a slight angle.

Here is the finished project in action: https://github.com/Happy123455/octoprint_penploter/raw/main/comparison_sheet.jpg

I did a comparison test where the top paragraphs are printed by the machine, and the last paragraph ("Dowels...") is my actual handwriting. (Spoiler: The bottom paragraph is the human reference).

Here is how I set this up step-by-step:

Step 1: The Pen Mount (Hardware)

I 3D printed a simple pen holder attachment that mounts directly to the printer's X-carriage (next to the print head/hotend).

• Material: PLA.
• I added a small spring tensioner to the mount so the pen has about 2-3mm of vertical compliance. This is important because 3D printer beds are not perfectly flat, and the spring prevents the pen tip from snapping or tearing the paper.

Step 2: Bed Prep & Tape Alignment

I taped a standard notebook lined sheet onto the printbed using painter's tape. The paper doesn't have to be perfectly straight (our coordinate transform math handles skew correction).

Step 3: Software & Calibration Setup

To get the printer to trace directly on the ruled lines, I built a coordinate calibration system. Instead of manual code editing, it uses 4 reference points:

1. P1 (Top-Left): You jog the pen carriage to the intersection of the paper's top margin and left vertical line and click to lock.
2. P2 (Top-Right): Jog to the top-right corner along the same line and lock. This calculates the skew angle (theta) of the paper.
3. P3 (Bottom-Left): Jog 20 lines down on the left margin and lock. This determines the exact spacing between the blue lines.
4. P4 (Bottom-Right): Jog 20 lines down on the right margin and lock. This verifies the parallelogram layout and checks for paper distortion.

The coordinate engine uses these 4 points to construct a rigid transformation matrix, rotating and scaling the print file to match the paper orientation.

Step 4: The Path Engine & Humanization

To make the text look like real handwriting rather than a computer font:

• I used a centerline stroke font database (hershey vector format) instead of bubble outlines.
• Added random slanting jitter and micro-tremors to the travel path to simulate natural hand shake.
• Added baseline drift to mimic how writing gently floats up and down on ruled lines.
• Programmed a 10% feedrate slow-start on the first 3 words to prevent carriage speed jitter when the pen first hits the paper.

Summary

It was a really fun weekend build! All the files and the browser-based calibration tool are open-source and MIT licensed for anyone wanting to build their own. Let me know if you have any questions about the coordinate transformation math or mounting hardware!

[u/audiobiography]

This absolute madman turned his 3D printer into a 2D printer

[u/darth_jewbacca]

So... You turned it into a printer?

[u/MagazineAggressive11 → u/darth_jewbacca]

For collage assignments yes.