homelab-docs/Printing/Key caps/README_scaling.md

Keycap Scaling Guide

Quick Start

1. Open the script: Open Body5_scaled.scad in OpenSCAD
2. Adjust scaling: Edit the body_scale_xy parameter at the top (default: 0.98 = 98%)
3. Preview: Press F5 to see a quick preview
4. Render: Press F6 to fully render (required before export)
5. Export: Go to File > Export > Export as STL
6. Test print: Print and check the fit
7. Iterate: Adjust the scale parameter and repeat if needed

Key Parameters

body_scale_xy

• Default: 0.98 (98% of original size)
• Purpose: Scales the X and Y dimensions of the keycap body
• Recommendations:
  • Start with 0.98 for a 2% reduction
  • If too tight: try 0.97 (3% reduction)
  • If too loose: try 0.99 (1% reduction)
  • Fine-tune: use 0.975, 0.985, etc.

body_scale_z

• Default: 1.00 (no scaling)
• Purpose: Scales the Z (height) dimension
• Recommendation: Keep at 1.00 to maintain keycap height

Stem Parameters (Advanced)

Only adjust these if the stem preservation isn't working correctly:

• stem_diameter: Diameter of the circular preservation region (default: 5.5mm)
• stem_height: Height of the stem (default: 4.0mm)
• stem_z_position: Vertical position offset (default: -2.0mm)
• $fn: Circle smoothness (default: 64, range: 32-128)

How It Works

The script uses a two-part approach:

1. Scaled Body: The entire keycap is scaled down by your chosen percentage, BUT a circular region around the stem is cut out
2. Original Stem: The circular stem region is preserved at 100% scale (keeping the 4mm × 4mm Cherry MX cross dimensions)
3. Combined: Both parts are merged together

This ensures:

• ✅ The outer keycap body fits better in sockets (scaled down)
• ✅ The Cherry MX stem remains exactly 4mm × 4mm (unscaled)
• ✅ The circular region around the stem is preserved (for off-brand switches)
• ✅ The stem stays centered and properly positioned

Workflow for Iterative Testing

1. Export STL with body_scale_xy = 0.98
2. Slice and print the keycap
3. Test fit on your keyboard
4. If too tight: Decrease scale (try 0.97)
5. If too loose: Increase scale (try 0.99)
6. If just right: You're done!

Troubleshooting

The stem looks wrong or is scaled

• The circular stem region might not be positioned correctly
• Measure your stem in the original STL
• Adjust stem_z_position, stem_diameter, or stem_height
• If the circle is too jagged, increase $fn to 128

The keycap won't render

• Make sure Body5.stl is in the same folder as the .scad file
• Check for errors in the OpenSCAD console (bottom of window)

Rendering is slow

• This is normal! The script imports the STL twice
• F5 preview is fast but lower quality
• F6 render is slow but required for STL export
• Consider reducing the preview quality in OpenSCAD preferences

The seam between body and stem is visible

• This is usually not noticeable in the printed part
• If needed, increase stem_diameter by 0.5mm increments (try 6.0mm or 6.5mm)

File Structure

Key caps/
├── Body5.stl              # Original keycap STL
├── Body5_scaled.scad      # OpenSCAD scaling script
└── README_scaling.md      # This guide

Export Settings

When exporting STL from OpenSCAD:

• File format: STL (binary is smaller, ASCII is more compatible)
• Units: millimeters (mm)

Next Steps

After exporting your scaled STL:

1. Import into your slicer (Cura, PrusaSlicer, etc.)
2. Use typical keycap print settings:
   • Layer height: 0.1-0.2mm
   • Infill: 15-20%
   • Supports: Probably not needed for most keycaps
3. Print and test!

---

Note: The Cherry MX stem dimensions (4mm × 4mm) are standardized. The script is designed to preserve these exactly, so you should only need to adjust the body_scale_xy parameter for tolerance testing.