Product FAQ's

Q: What is a keyed screw jack?

A: Some loads do not prevent lifting screw rotation-these applications require a keyed jack. A key, fixed to the jack housing and inserted into a keyway milled into the lifting screw, forces the lifting screw to translate without rotating. Several dimensions of keyed jacks differ from normal jacks-check the keyed jack drawings for each jack model. You can view a keyed jack in the Engineering Overview - Jack Designs PDF document.


Q: What is a Keyed For Traveling Nut (KFTN) screw jack?

A: A keyed for traveling nut jack (sometimes referred to as a rotating screw jack) features a lifting screw keyed to the worm gear as a single unit, forcing the lifting screw to rotate, but not translate. A flanged traveling nut, attached to the load, is driven by the rotation of the lifting screw. This type of jack is ideal for applications that cannot accommodate a screw protection tube or require a flush mount. Refer to the keyed for traveling nut dimensional drawing for each jack model. You can view a keyed for traveling nut jack in the Engineering Overview - Jack Designs PDF document.


Q: How do I calculate linear travel speed of a screw jack?

A: Each screw jack has an inherent number of input shaft turns per inch (TPI) of screw travel. TPI is simply the result of the jack's gear ratio divided by screw lead. The TPI can be found on the jack specification pages at the beginning of each jack section. When the input RPM is divided by the TPI, the result is the linear speed of travel in inches per minute.  Example: A model WJT 242 has a TPI of 96, if 350 RPM is applied to the input shaft, the resultant linear speed is (350/96) or 3.65 inches per minute.


Q: How fast can I move a load with a screw jack?

A: Machine screw jacks are designed to move loads at a typical rate of 10-22 inches per minute. For higher speeds, consider Ball Screw Jacks, Bevel Gear® Jacks, or Bevel Ball Actuators. For application assistance, please contact us directly via phone or email.


Q: What is meant by "duty cycle"?

A: An application duty cycle is the relationship between run time and total cycle time.
Example: If a jack is on for 5 seconds of every minute, the duty cycle = 5/60, or 8.3%.


Q: What is the allowable duty cycle of a screw jack?

A: The allowable duty cycle is based upon several application variables such as load, speed, and temperature. For application assistance, please contact us directly via phone or email.


Q: How do I calculate required input torque/horsepower?

A: Locate the Operating Torque Constant found on the jack specification pages at the beginning of each jack section. To calculate horsepower, multiply this constant times your load and divide by 63,025.

Example: WJT 242 has a torque constant of .009W with (W) representing the load. Using a 2000 pound load you have (.009 x 2000) = (18 inch lbs. of input torque) at the worm shaft. The formula for horsepower is (Input RPM x Input Torque/63025). Using 350 input RPM you have (350 x 18 / 63025) = .10 or approximately 1/10 HP required.

Note: Unlike Bevel Gear ® and Bevel Ball Actuators, Joyce Machine Screw Jack torque constants vary with speed, therefore the constants listed in the catalog are only accurate for the RPM listed. To calculate horsepower at speeds other than those listed, please contact Trans-Quip Inc.


Q: What is the difference between upright and inverted jack configurations?

A: The difference between an upright and inverted jack is the location at which the jackscrew exits the jack relative to the jack base. For example, an upright jack's lifting screw exits the jack opposite the base. An inverted jack's lifting screw exits the jack on the same side as the base. The choice between an inverted or upright jack is totally dependent upon your application. Upright and inverted jacks can be viewed on any of the jack drawings.

Note: An upright jack mounted upside down is still referred to as an upright jack.


Q: Can a Joyce screw jack backdrive? Does it require a braking device?

A: Most machine screw jacks will not be backdriven, that is, power to the input shaft is required for travel in both directions. Some exceptions include the standard WJ 500 and some DWJ (double lead) models. Under extreme vibration conditions any machine screw jack has the potential to backdrive. Brakemotors should be considered for all these exceptions.

Note: Bevel Ball and Ball screw Jacks will backdrive. Brakemotors are a requirement.


Q: What is the maximum allowable travel of a screw jack?

A: Either the column loading in compression or the availability of screw stock generally limits the maximum allowable travel. Go to Column Load Charts for limitations for guided, trunnion, and unguided conditions. For travels over 20 feet, please contact Trans-Quip.