Pen Plotter

A custom pen plotter designed in Onshape to draw physical 2D artwork with a moving pen carriage.

Why I Built This

I wanted to make a drawing machine that turns digital designs into real pen strokes. The challenge I am working through is making the mechanical system smooth enough that the plotter draws clean lines instead of shaky ones: the frame needs to stay square, the carriage needs to move predictably, and the pen holder needs to lift and lower without throwing off alignment.

What It Does

This project is a hardware pen plotter. The design includes a frame, belt/idler motion system, gantry, moving cart, toolhead, pen housing, stepper motors, and a servo-driven pen lift.

Current capabilities:

CAD assembly designed in Onshape
Bill of materials exported and cleaned
Firmware folder scaffolded
CAD exports, photos, and final firmware still in progress

Project Links

Onshape CAD:

https://cad.onshape.com/documents/21408afa0678dfc090a39137/w/cada99e8b20e026a88815622/e/614e2d6018b77ddf107765d2?renderMode=0&leftPanel=false&uiState=6a7a26314284ccba60f59ccc

Bill of materials:

docs/bom.md
docs/bom.csv

How It Fits Together

The plotter is organized around a rigid frame and a moving gantry/toolhead system.

Frame and corner brackets
  hold the plotter square and support the belt/idler stacks

Stepper motors and pulleys
  drive the belt motion

Gantry extrusion and cart plates
  carry the moving toolhead across the drawing area

Toolhead and pencil housing
  hold the pen and handle pen lift/lower motion

Firmware
  will control motor movement, servo position, homing, and plot commands

Photos

Hardware photos and CAD screenshots will go in photos/.

Needed before shipping:

photos/cad-overview.png       Screenshot or render of the full CAD assembly
photos/frame-build.jpg        Frame/corner bracket build photo
photos/toolhead.jpg           Pen holder or moving cart photo
photos/first-plot.jpg         Photo of the plotter drawing or its first output

Repository Layout

docs/
  bom.md        Clean human-readable bill of materials
  bom.csv       Clean spreadsheet-friendly bill of materials

exports/
  stl/          STL files for printed parts
  drawings/     PDF or DXF drawings
  *.step        Full CAD exports

firmware/
  README.md     Firmware notes and planned controls
  src/          PlatformIO or C/C++ source
  include/      Shared headers
  arduino/      Arduino IDE sketches

photos/
  Build photos, CAD screenshots, and plot output images

How to Reproduce It

1. Open the Onshape CAD link above.
2. Review the cleaned bill of materials in docs/bom.md.
3. Export the full assembly from Onshape as a STEP file and place it in exports/.
4. Export printable parts as STL files and place them in exports/stl/.
5. Build the frame and motion system from the CAD and BOM.
6. Add electronics and firmware once the controller board is chosen.
7. Add build photos and a first-plot photo to photos/.

Setup Instructions

For CAD review:

1. Open the Onshape link in a browser.
2. Use the Assembly tab to inspect the full mechanism.
3. Use the BOM in docs/bom.md to match parts to the design.

For local files:

git clone https://github.com/Photun/pen-plotter.git
cd pen-plotter

For firmware:

Firmware upload instructions will be added after the controller board and motor driver setup are finalized.

Onshape Export Instructions

For the full assembly:

1. Open the assembly tab in Onshape.
2. Right-click the assembly tab at the bottom.
3. Choose Export.
4. Pick STEP.
5. Save the file into exports/.

For 3D printing:

1. Open the Part Studio or Assembly containing the printable part.
2. Right-click the part or tab.
3. Choose Export.
4. Pick STL.
5. Save individual files into exports/stl/.

Current Status

Design: in progress in Onshape
BOM: cleaned and uploaded
CAD exports: not uploaded yet
Firmware: scaffold added, code not written yet
Build photos: not uploaded yet

License

This project is licensed under the MIT License. See LICENSE.