Glossary of Terms

Acceleration/Deceleration Profile Back to top>
A term used to describe the percentage of time, during a move, that is used for acceleration (and for deceleration) relative to the total amount of time used for that move. The formulas used in this guide assume a 25% acceleration/deceleration profile, as shown below.

Axial Lash Back to top>
The free movement between a screw and a nut as measured along the axis.

Axial Center Load Back to top>
Any load which is distributed evenly about the axis of a screw. These loads are desirable.

Backdrive Back to top>
Rotation (torque) of a screw caused by a load (thrust) on the nut.

Backlash Back to top>
The amount of free movement between a screw and a nut. Axial Lash is measured along a screws axis, while radial or transverse backlash is measured transverse to the screw.

Compression Load Back to top>
A load that compresses a screw along its axis. When designing a system, minimize this load type.

Critical Speed Back to top>
The maximum speed, normally expressed in revolutions per minute, that a shaft can rotate before it experiences damaging harmonic vibrations. This value varies with a shafts length, diameter, straightness and mounting configuration. When considering a drive system, this speed is often converted to a measure of linear distance versus time for convenience purposes.

Efficiency Back to top>
The percentage of torque put on a screw that gets converted to thrust in the nut.

End Fixity Back to top>
Various methods for supporting the ends of a rotating shaft, each providing a different level of rigidity.

External Guiding Back to top>
A means of supporting and guiding a carriage to assure that nut loading occurs along the axis of the drive screw.

Flank Angle Back to top>
The angle between the helix of a screw and a plane that is perpendicular to the screws axis. The value is a calculated, based on the lead and the diameter of a screw.

Friction Back to top>
The resistance to relative motion between objects that contact each other. When such objects slide or roll on each other, this resistance converts input energy to heat, causing a reduction in efficiency.

Hard Stop Back to top>
A mechanical means of stopping a carriage in an exact position by running into a fixed stop. Shocks are advised, and deceleration is necessary before reaching a hard stop in order to achieve maximum drive life.

Index Back to top>
The distance a carriage can travel along the axis of a drive system without interference.

Lead Back to top>
The axial distance a nut moves during one revolution of a screw. (Equal to pitch of the screw multiplied by the number of starts on the screw)

Lead Error Back to top>
Deviation from the specified lead, which results from the manufacturing variations of a screw. Normally expressed per linear foot, these errors are cumulative over the length of a screw.

Load Back to top>
The weight that is being moved by a drive system.

Load Surface Area Back to top>
The amount of surface area of the nut that is in contact with the drive screw when it is under a load. This area is where the flanks of the nut and screw make contact and is equal to _ of the total thread surface in the nut.

Major Diameter Back to top>
For a screw it is the diameter at the crest of the threads, while for a nut it is the diameter at the root of the threads.

Minor Diameter Back to top>
For a screw it is the diameter at the root of the threads, and for a nut it is the diameter at the crest of the threads.

Motion Profile Back to top>
The entire set of motions a drive system will repeatedly undergo while performing all of its tasks.

Move Back to top>
A single linear movement in the motion profile of a drive system. All parameters in all moves of a profile must be considered to obtain an accurate life prediction of a TranTek drive system.

Off Center Moment Load Back to top>
Any load that is neither along the axis of a screw nor perpendicular to it, resulting in forces that cause the nuts centerline to misalign with the screws centerline. Avoid loads of this type.

Pitch Back to top>
The distance between the threads of a screw as measured along the axis of the screw.

Radial Load Back to top>
Any load which is perpendicular to the axis of the screw. Avoid loads of this type.

Re-cast Back to top>
A procedure performed at TranTek, whereby worn epoxy composite is removed from a nut housing, then new threads are cast, bringing it back to its original specifications.

System Life Back to top>
The number of years that a properly designed and maintained TranTek drive system will operate before the axial lash reaches a predetermined value. (Usually .030”, at which time the nut can be replaced and/or the worn nut can be sent back to TranTek to be re-cast)

Standoff Back to top>
A TranTek support used to join screws together and allow the DriTran nut to pass right over.

Starts Back to top>
The number of individual thread paths on a screw.

Tension Load Back to top>
Any load that stretches a screw along its axis. When designing a system, maximize this load type.

Thread Clearance Back to top>
DriTran epoxy composite nuts are cast with .002” to .005”of linear thread clearance, also known as axial lash. Thread clearance provides room for lubrication, and it increases over the life of the drive system, as the epoxy composite slowly wears.

Transfer Distance Back to top>
See Index.