Choose drive torque, axial force, screw lead or efficiency, then enter the displayed values. This lead-screw model estimates rotary-to-linear drive torque; actual static breakaway torque may require additional friction and drag data.

Estimate lead-screw drive torque using T = F ร— L รท (2ฯ€ ร— ฮท). Blank optional efficiency means an ideal, frictionless screw (ฮท = 1). This does not independently predict static breakaway friction.

Load force along the screw axis. Changing units converts the value.

Linear travel per revolution, not thread pitch for a multi-start screw. Suggestions include 1, 2, 5, 8, 10 mm and 0.05, 0.1 in; 20/10 TPI applies only to single-start screws.

Screw efficiency (optional)

Blank = 1 (ideal). Enter 0.30 for 30%. Suggestions are examples, not ratings for your screw; verify manufacturer data.

Breakaway Torque Formula

The following example problem outlines the steps and information needed to calculate the Breakaway Torque.

BT = (BF ร— SL) / (2ฯ€)

Note: The formula above is the ideal (100% efficient, frictionless) lead screw relationship based on work per revolution, where SL is the screw lead (linear travel per revolution). For a more realistic estimate that accounts for friction and other losses, include an overall efficiency factor ฮท (greater than 0 and at most 1). Blank optional efficiency uses 1. This does not separately account for bearing/nut drag, inertia or static starting friction:

BT = (BF ร— SL) / (2ฯ€ eta)

Variables:

  • BT is the estimated screw drive torque (lbf-in)
  • BF is the axial load force (lbf)
  • SL is the screw lead (in)
  • ฮท is the overall screw efficiency (unitless, greater than 0 and at most 1)

To calculate a breakaway torque (ideal), multiply the breakaway force by the screw lead, then divide by 2 times pi. To include losses, divide by (2ฯ€ ร— ฮท) instead.

How to Calculate Breakaway Torque?

The following steps outline how to calculate the Breakaway Torque.

  1. First, determine the breakaway force (lbf). 
  2. Next, determine the screw lead (in). 
  3. Next, gather the formula from above = BT = BF * SL / (2*pi).
  4. Select Drive torque, enter the force and lead, optionally enter a verified screw efficiency, then select Calculate.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

breakaway force (lbf) = 300

screw lead (in) = 5

BT = BF * SL / (2*pi) = ?

BT = (300 ร— 5) / (2ฯ€) = 1500 / 6.283185… โ‰ˆ 238.7324 lbf-in