Pen Plotter Project Update

🛠️ Pen Plotter Project Update – Engineering a Modular Steel Frame System

It’s fascinating how quickly a project's direction can evolve once physical components come together. As soon as I began printing the initial parts for my pen plotter, a surge of new ideas prompted a complete redesign.

🔧 Transitioning from Board-Based to Steel Frame Architecture

My original concept was straightforward: mount everything onto a plywood board. However, assembling just a few components immediately highlighted the limitations of that approach. I pivoted toward designing a robust steel tubing frame, with the board now mounted onto it, reversing the original hierarchy.

This adjustment wasn’t merely structural — it marked a conceptual shift. The new framework is modular and overengineered by design, allowing future integration of additional tools and systems. It’s essentially a customizable set of linear actuators, built with adaptability in mind.

🔩 Mechanical Design Overview

Each actuator is built with simplicity and efficiency:

• A custom bracket holds the stepper motor firmly in place.
• A tensioning system is mounted on the opposite end of the tubing.
• A linear rail is directly affixed to the steel tubing.
• A timing belt links the motor to the moving carriage, delivering controlled, precise motion.

The timing belts have proven highly effective. Their easy tensioning and smooth motion transmission make them ideal for the current setup. Once properly aligned, the carriage movement becomes seamless and reliable.

To attach the actuators to the frame, I’m using three screws per side, with several nuts per screw to allow fine vertical adjustments. This adjustability compensates for imperfections in the steel tubing, which isn’t perfectly straight.

🧪 Initial Motion Tests

I ran a preliminary test plotting a circle using basic G-code — and it worked! Witnessing the machine operate for the first time was a significant milestone.

Currently, the electronics are temporarily suspended in open air, solely for testing purposes. A dedicated enclosure will be added later. Despite this temporary setup, seeing the mechanical system come alive was incredibly rewarding.

⚠️ Structural Challenges and Solutions

The initial frame lacked sufficient rigidity. The plywood board used as the structural base was slightly warped, which led to instability when adjusting actuator height; the frame would flex under load.

To remedy this, I’m now constructing the base using more robust 1" x 1.5" steel tubing. I’m also considering replacing the board with a thinner or more dimensionally stable material, relegating it to serve purely as a working surface.

🔌 Electronics and Step Generation Constraints

The motion system runs on TMC2208 stepper drivers paired with an Arduino. However, I encountered an issue with the Z-axis: the high microstepping resolution of the drivers exceeded the Arduino’s step generation capabilities.

Changing the microstepping configuration requires UART communication, which I have not yet implemented. Until that’s resolved, the Z-axis will remain a bottleneck.

That said, I’m thoroughly impressed by the TMC drivers. They are exceptionally quiet — it’s almost surreal to watch the carriage glide silently across the frame. This low-noise performance adds a refined, professional quality to the machine, making the testing process genuinely enjoyable.

One small but impactful improvement: I recently acquired a proper Dupont connector crimper. It significantly streamlined the wiring process, resulting in cleaner, more dependable connections.

📸 Coming Soon

I’ll be sharing media shortly, including:

• Detailed photos of the new bracket and actuator assemblies.
• A video showing the circle test plot in action.
• CAD captures illustrating the updated design.

More to come — the development is just getting exciting!