Calculate General Purpose Acme Thread Form (ASME B1.5) dimensions.
Calculation Results
Parameter
Value (inches)
Pitch (p)
–
Basic Thread Height (h)
–
Pitch Diameter (Basic)
–
Minor Diameter (Basic)
–
Crest Width (Basic)
–
Root Width (Basic)
–
Note: These are basic nominal dimensions based on the 29° General Purpose Acme Thread form. Actual manufacturing requires applying tolerances (Class 2G, 3G, 4G) based on fit requirements.
Understanding Acme Threads
Acme threads are a specific thread profile characterized by a 29° included angle. Unlike the standard 60° V-threads found on common bolts and screws, Acme threads are trapezoidal in shape. This robust profile makes them ideal for power transmission applications where heavy loads need to be moved linearly.
Key Characteristic: The 29° thread angle allows for the use of a split nut, which can be engaged or disengaged from the lead screw, a feature often used on lathe lead screws.
How to Use This Calculator
This calculator determines the basic geometric dimensions required to machine or inspect a General Purpose Acme thread. Here is how to interpret the inputs:
Major Diameter: The largest diameter of the thread (the outside of the screw). Common sizes range from 1/4 inch up to 5 inches or more.
Threads Per Inch (TPI): The count of thread peaks along one inch of the screw length. Coarser threads (lower TPI) move the load faster per rotation but require more torque.
Calculated Parameters Explained
The results provided above correspond to the standard ASME B1.5 formulas:
Pitch (p): The distance between corresponding points on adjacent threads. Calculated as 1 / TPI.
Pitch Diameter: The theoretical cylinder where the tooth width equals the space width. This is the critical dimension for thread fit.
Thread Height (h): The depth of the thread from the crest (top) to the root (bottom). For standard Acme, this is half the pitch.
Crest & Root Width: These dimensions determine the flat surfaces at the top and bottom of the thread profile, essential for cutting tool geometry.
Common Applications
Acme threads are ubiquitous in machinery requiring high load capabilities and precision movement. You will commonly find them in:
Lead screws on lathes and milling machines.
Bench vises and C-clamps.
Valve stems for industrial piping.
Linear actuators and jacks.
Stub Acme vs. General Purpose
While this calculator focuses on the "General Purpose" form, there is also a "Stub Acme" standard. Stub Acme threads have a shorter thread height (usually 0.3p or 0.433p) and are used where the deep thread of the standard Acme is not required or where radial space is limited. Always verify which standard your blueprint specifies before machining.
function calculateAcme() {
// Clear errors
var errorDiv = document.getElementById("error-message");
errorDiv.style.display = "none";
errorDiv.innerHTML = "";
// Get Inputs
var majorDiaInput = document.getElementById("majorDia").value;
var tpiInput = document.getElementById("tpi").value;
// Validation
if (majorDiaInput === "" || tpiInput === "") {
errorDiv.innerHTML = "Please enter both Major Diameter and TPI.";
errorDiv.style.display = "block";
return;
}
var majorDia = parseFloat(majorDiaInput);
var tpi = parseFloat(tpiInput);
if (isNaN(majorDia) || isNaN(tpi) || majorDia <= 0 || tpi Major Dia – Pitch
// Crest Width = 0.3707 * Pitch
// Root Width = (0.3707 * Pitch) – 0.0052 (Basic nominal derived from tool point width)
var pitch = 1.0 / tpi;
var height = 0.5 * pitch;
var pitchDia = majorDia – (0.5 * pitch);
var minorDia = majorDia – pitch;
// Basic Crest Width
var crestWidth = 0.3707 * pitch;
// Basic Root Width (Formula: 0.3707p – 0.0052)
// Note: For very fine pitches, the -0.0052 constant might make this negative theoretically,
// though standard Acme isn't usually made that small. We will clamp at 0 for safety.
var rootWidth = (0.3707 * pitch) – 0.0052;
if (rootWidth < 0) rootWidth = 0;
// Display Results
document.getElementById("res-pitch").innerText = pitch.toFixed(4) + '"';
document.getElementById("res-height").innerText = height.toFixed(4) + '"';
document.getElementById("res-pitch-dia").innerText = pitchDia.toFixed(4) + '"';
document.getElementById("res-minor-dia").innerText = minorDia.toFixed(4) + '"';
document.getElementById("res-crest").innerText = crestWidth.toFixed(4) + '"';
document.getElementById("res-root").innerText = rootWidth.toFixed(4) + '"';
// Show result area
document.getElementById("results-area").style.display = "block";
}