Consult your tool manufacturer or material charts.
Please enter valid positive numbers for all fields.
Spindle Speed
0RPM
Feed Rate
0IPM
function updateLabels() {
var system = document.getElementById('unitSystem').value;
if (system === 'imperial') {
document.getElementById('lblDiameter').innerText = 'Drill Diameter (in)';
document.getElementById('lblSpeed').innerText = 'Surface Speed (SFM)';
document.getElementById('lblChipLoad').innerText = 'Chip Load per Tooth (ipt)';
document.getElementById('diameter').placeholder = 'e.g. 0.5';
document.getElementById('surfaceSpeed').placeholder = 'e.g. 100';
document.getElementById('chipLoad').placeholder = 'e.g. 0.004';
} else {
document.getElementById('lblDiameter').innerText = 'Drill Diameter (mm)';
document.getElementById('lblSpeed').innerText = 'Surface Speed (m/min)';
document.getElementById('lblChipLoad').innerText = 'Chip Load per Tooth (mm/tooth)';
document.getElementById('diameter').placeholder = 'e.g. 12';
document.getElementById('surfaceSpeed').placeholder = 'e.g. 30';
document.getElementById('chipLoad').placeholder = 'e.g. 0.1';
}
// Hide results when unit changes to avoid confusion
document.getElementById('results').style.display = 'none';
}
function calculateDrillSpeeds() {
// 1. Get Values
var system = document.getElementById('unitSystem').value;
var D = parseFloat(document.getElementById('diameter').value);
var Vc = parseFloat(document.getElementById('surfaceSpeed').value);
var T = parseFloat(document.getElementById('flutes').value);
var CL = parseFloat(document.getElementById('chipLoad').value);
var errorMsg = document.getElementById('errorMessage');
var resultsBox = document.getElementById('results');
// 2. Validation
if (isNaN(D) || isNaN(Vc) || isNaN(T) || isNaN(CL) || D <= 0 || Vc <= 0 || T <= 0 || CL <= 0) {
errorMsg.style.display = 'block';
resultsBox.style.display = 'none';
return;
}
errorMsg.style.display = 'none';
var rpm = 0;
var feed = 0;
var feedUnit = '';
// 3. Calculation Logic
if (system === 'imperial') {
// RPM = (SFM * 3.82) / Diameter
// Exact formula: (SFM * 12) / (PI * D)
rpm = (Vc * 3.8197) / D;
// Feed (IPM) = RPM * T * CL
feed = rpm * T * CL;
feedUnit = 'IPM';
} else {
// Metric
// RPM = (Vc * 1000) / (PI * Diameter)
rpm = (Vc * 1000) / (Math.PI * D);
// Feed (mm/min) = RPM * T * CL
feed = rpm * T * CL;
feedUnit = 'mm/min';
}
// 4. Display Results
document.getElementById('resRPM').innerText = Math.round(rpm).toLocaleString();
document.getElementById('resFeed').innerText = feed.toFixed(2);
document.getElementById('resFeedUnit').innerText = feedUnit;
resultsBox.style.display = 'block';
}
Understanding Drill RPM and Feed Rates
Calculating the correct RPM (Revolutions Per Minute) and Feed Rate is critical for machining efficiency, tool life, and surface finish. Whether you are using a manual drill press or a high-end CNC machine, understanding the relationship between surface speed, tool diameter, and chip load is the foundation of successful drilling.
What is Surface Speed (SFM)?
Surface Feet Per Minute (SFM) or Surface Speed measures how fast the outer edge of the tool moves across the material. It is determined primarily by the hardness of the material you are cutting and the material of the drill bit (High-Speed Steel vs. Carbide).
Softer materials (Aluminum, Brass) allow for higher SFM.
Below is a general starting point for Surface Speeds (SFM) using HSS (High-Speed Steel) drills. Note: Carbide tools generally run 2-3x faster.
Material
Surface Speed (SFM)
Surface Speed (m/min)
Aluminum
200 – 300
60 – 90
Low Carbon Steel
80 – 100
24 – 30
Stainless Steel (300 Series)
40 – 60
12 – 18
Tool Steel
40 – 50
12 – 15
Brass / Bronze
150 – 200
45 – 60
Why Chip Load Matters
Chip load (or feed per tooth) represents the thickness of material removed by each cutting edge during one revolution. If the chip load is too low, the tool rubs rather than cuts, generating heat and work-hardening the material. If it is too high, the tool may break. For standard twist drills, chip load often correlates to the drill diameter (e.g., a 0.5″ drill might handle 0.005″ – 0.008″ per rev, divided by 2 flutes).