Anti-backlash nuts are available in many styles. Selecting the right nut style for your project depends on various factors, including; payload, accuracy, repeatability requirements, budget, space constraints, and available torque. Linear accuracy, often referred to as lead error, is a function of the leadscrew quality. Repeatability is a function of the nut. In many cases, bi-directional repeatability (returning to the same position each time) is more important than linear point A to point B accuracy. Repeatability can often be compensated for in the system once that value is known.
Axial anti-backlash nuts consist of two nut halves biased against opposite flank angles with a compression spring. This configuration provides the simplest means of taking up backlash at the lowest cost. The disadvantage of this design is the resulting higher drag torque. This nut’s stiffness is dependent on the force of the spring. However, multiple springs options are available and can be sized appropriately depending on the application.
Radial style anti-backlash nuts have three fingers that close like a collet to squeeze the threads of the nut into the flank angle of the leadscrew, removing the backlash. The accompanying compression spring provides constant pressure to compensate for wear. This style offers greater stiffness than an axial anti-backlash nut and is ideal for higher loads and better repeatability while keeping costs low.
The anti-backlash nut with the highest design load rating and greatest bi-directional repeatability is a torsional anti-backlash nut. A spacer separates two nut halves and automatically adjusts with the use of a torsion spring to lengthen and take up the gap as wear occurs. This automatic adjustment ensures that the nut maintains zero backlashes. Though mid-range in price, this design offers the highest stiffness while at the same time providing the lowest drag torque.
When standard anti-backlash nuts do not satisfy all of your project criteria, a custom nut may be the solution. Modifications can be as simple as a material change (such as PEEK for medical uses or bronze for industrial projects) or a different mounting flange to suit the space and preferred attachment method. Or, your application may warrant a completely custom anti-backlash nut requiring a rework of the axial, radial, and torsional principles. These can be shaped to maximize stroke length, increase life, eliminate other components, and reduce assembly time.