Coefficient of Friction of Power Screw given Torque Required in Lifting Load with Acme Thread Calculator

Coefficient of Friction Formula:

\[ \mu = \frac{2 \cdot T - W \cdot d_m \cdot \tan(\alpha)}{\sec(0.253) \cdot (W \cdot d_m + 2 \cdot T \cdot \tan(\alpha))} \]

Torque for lifting load (T):

N·m

Load on screw (W):

Mean Diameter of Power Screw (d_m):

Helix angle of screw (α):

rad

Tolerance:

Coefficient of friction (μ):

Tolerance Range (±5%):

1. What is Coefficient of Friction of Power Screw?

Definition: This calculator determines the coefficient of friction in an Acme threaded power screw system when lifting a load, based on the required torque and screw parameters.

Purpose: It helps mechanical engineers and designers evaluate the friction characteristics of their screw thread system.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ \mu = \frac{2 \cdot T - W \cdot d_m \cdot \tan(\alpha)}{\sec(0.253) \cdot (W \cdot d_m + 2 \cdot T \cdot \tan(\alpha))} \]

Where:

\( \mu \) — Coefficient of friction at screw thread
\( T \) — Torque for lifting load (N·m)
\( W \) — Load on screw (N)
\( d_m \) — Mean diameter of power screw (m)
\( \alpha \) — Helix angle of screw (radians)
0.253 — Angle corresponding to Acme thread profile (≈14.5°)

3. Importance of Friction Coefficient Calculation

Details: Accurate friction coefficient estimation is crucial for determining screw efficiency, self-locking capability, and required driving torque.

4. Using the Calculator

Tips: Enter the torque, load, screw diameter, helix angle, and tolerance percentage. All values must be positive (except angle can be zero).

5. Frequently Asked Questions (FAQ)

Q1: What's a typical coefficient for Acme threads?
A: Typically ranges from 0.1 to 0.3 depending on materials and lubrication.

Q2: Why is there a sec(0.253) term?
A: This accounts for the 29° included angle of Acme threads (0.253 radians ≈ 14.5° half-angle).

Q3: How do I determine the helix angle?
A: \( \alpha = \arctan(\frac{p}{\pi \cdot d_m}) \), where p is the screw pitch.

Q4: What does the tolerance percentage mean?
A: It shows the ± range around the calculated value to account for real-world variations.

Q5: Can this be used for other thread types?
A: No, this formula is specific to Acme threads. Other thread forms require different calculations.