Excellon drill format

README.md

Experiment for creating .drl drill files.

These are used in the process of fabricating PCBs (printed circuit boards), they specify where the laser/mechanical drills should drill holes.

The format is also known as Excellon.

Excellon Specification

https://gist.githubusercontent.com/katyo/5692b935abc085b1037e/raw/32879038a55e1e7019902d8d073d6f5d6d2e45ff/excellon.md

Usage

# generate .drl file
bun index.js | tee example.drl

# view in gerber file viewer
gerbv example.drl

holes.json5

// `x`, `y` are the coordinates
// `tool` is the drill bit diameter
[
  { x: 0, y: 0,    tool: 0.2 },
  { x: 0, y: 0.2 , tool: 0.4 },
  { x: 0, y: 0.3 , tool: 0.2 }
]

index.js

import fs from 'fs'
import json from 'json5'

function mapTools(holes) {
  const tools = new Set()
  const indexes = new Map()

  let count = 0

  holes.forEach(({ tool }, index) => {
    if (!tools.has(tool)) {
      tools.add(tool)
      indexes.set(tool, ++count)
    }
  })

  return { tools, indexes }
}

class ExcellonWriter {
  constructor(holes, options = { unit: 'inch' }) {
    this.holes = holes
    this.options = options
    
    const { tools, indexes } = mapTools(holes)

    this.tools = tools
    this.indexes = indexes
  }

  write(io) {
    // start header
    io.write('M48\n')
    // use format 2 commands
    io.write('FMAT,2\n')

    // specify measurement unit (inch or metric)
    io.write(`${this.options.unit.toUpperCase()}\n`)

    // specify tools
    this.indexes.forEach((tool, index) => {
      io.write(`T${index}C${tool}\n`)
    })

    // end header
    io.write('%\n')

    // absolute mode
    io.write('G90\n')

    // drill mode
    io.write('G05\n')

    // specify holes
    this.holes.forEach((hole) => {
      const index = this.indexes.get(hole.tool)

      // choose tool
      io.write(`T${index}\n`)

      // specify drill position
      io.write(`X${hole.x}Y${hole.y}\n`)
    })

    // select no tool
    io.write('T0\n')

    // end file
    io.write('M30\n')
  }
}

// load drill holes
const data = await fs.promises.readFile('./holes.json5')
// parse json
const holes = json.parse(data)
// create writer
const writer = new ExcellonWriter(holes, { unit: 'inch' })
// output .drl format
await writer.write(process.stdout)