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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 on the Jack Designs page.
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 on the
Jack Designs page.
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, fill out the
Jack/Actuator Selection
Guide and email it to our office.
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, fill out the
Jack/Actuator Selection
Guide and email it to our office.
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 fill out the
Jack/Actuator Selection Guide
and email it to our office.
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 Joyce.
Q. What are the benefits of a Linear Actuator?
A. Joyce/Dayton Linear Actuators offer a complete package solution including actuator,
motor, limit switches, and position feedback (potentiometer)
Q. What are the duty cycle limitations?
A. Joyce/Dayton actuators have been designed and thoroughly tested to meet the duty
cycles indicated in the catalog pages under the full load rating of the actuator. No
special capacitors or other components are required to meet rated duty cycle.
Q. What happens if I lose power?
A. The actuator will come to a stop and stay in position until power is re-applied.
An integral coil spring brake automatically engages when the motor is not running.
Q. What is the clutch and how is it used?
A. A screw clutch device is available on units without limit switches. This device
allows the screw to turn if the actuator is run against a hard stop. The clutch is an
emergency protection device and should not be repeatedly used as an end of travel limit.
Q. Are the linear actuators user-serviceable?
A. A comprehensive O&M manual is supplied with each actuator and some components
can be replaced in the field. However, it is often more convenient and cost effective
to replace the entire actuator.
Q. Are the limit switches pre-set?
A. Models with limit switches must be installed prior to setting the limit switch.
This allows the flexibility to tailor the stop positions to the individual application.
Q. What are the benefits of an integrated actuator?
A. Integrated actuators offer maximum design flexibility with a choice of gear ratios,
cast NEMA 56C motor mounting, and a choice of precision ACME screw or high speed ball
screw drives.
Q. Are integrated actuators self-locking?
A. The IA51 and IA201 integrated actuators are inherently self-locking. All other
models require a motor brake or other external locking device.
Q. What motor options are available?
A. Joyce/Dayton Integrated Actuators come standard with a NEMA 56C motor mounting so
any motor with a 56C mounting can be adapted. Integrated Actuators can be purchased
with AC or DC electric motors as well as with air motors.
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