Helix Angle of Power Screw given Effort Required in Lifting Load with Acme Threaded Screw Calculator

Helix Angle Formula:

\[ \alpha = \arctan\left(\frac{P_{li} - W \times \mu \times \sec(0.253)}{W + P_{li} \times \mu \times \sec(0.253)}\right) \]

Helix angle of screw:

rad

1. What is Helix Angle of Power Screw?

Definition: The helix angle is the angle between the helix of the thread and a line perpendicular to the screw axis.

Purpose: It's crucial for determining the mechanical advantage and efficiency of power screws, especially in lifting applications.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ \alpha = \arctan\left(\frac{P_{li} - W \times \mu \times \sec(0.253)}{W + P_{li} \times \mu \times \sec(0.253)}\right) \]

Where:

\( \alpha \) — Helix angle (radians or degrees)
\( P_{li} \) — Effort in lifting load (N)
\( W \) — Load on screw (N)
\( \mu \) — Coefficient of friction (dimensionless, ±5%)
0.253 — Angle of Acme thread (≈14.5° in radians)

Explanation: The formula accounts for the equilibrium between applied effort, load, friction, and the Acme thread geometry.

3. Importance of Helix Angle Calculation

Details: Proper helix angle calculation ensures optimal screw performance, preventing self-locking when not desired or ensuring it when needed.

4. Using the Calculator

Tips: Enter the effort in newtons, load in newtons, and coefficient of friction (default 0.15). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Why is the coefficient of friction marked ±5%?
A: Friction coefficients can vary due to material variations, lubrication, and surface finish, so we indicate a typical tolerance.

Q2: What's special about Acme threads?
A: Acme threads have a 29° included angle (14.5° per side), which provides better load-bearing capability than square threads.

Q3: When would I need to calculate the helix angle?
A: When designing power screws for jacks, presses, or other lifting applications where efficiency and self-locking are important.

Q4: How does helix angle affect screw performance?
A: Larger helix angles increase efficiency but may reduce self-locking capability; smaller angles do the opposite.

Q5: What's a typical coefficient of friction for power screws?
A: For steel-on-steel with lubrication, typically 0.1-0.2; for dry conditions, 0.2-0.3.