BACKLASH ON THE WORM SCREW
The worm screw – worm wheel coupling has a small degree backlash. Due to the reduction ratio and the transformation from the rotation movement to the translation movement, this backlash becomes an error of less than 0,05 mm in the linear positioning of the threaded spindle.

LATERAL BACKLASH IN TP MODELS
The thread spindle and worm wheel coupling presents a natural and necessary lateral backlash indicated by A in the drawing below. The use of a double serial guide allows to minimize the entity of said backlashes, while keeping the spindle and support nut axes aligned. The angular backlash on the coupling is translated on the spindle end fitting into a linear measure whose value depends on the size of the screw jack and grows according to the length of the spindle itself. Traction loads tend to reduce this backlash, while compression loads induce the opposite effect.

LATERAL BACKLASH IN TPR MODELS
In TPR models the spindle and the worm wheel are locked by means of a double pins. UNIMEC carries out this operation by means of a suitable machine which keeps the axes of the two components coincident during the two drillings and the consequent pins insertions. Hence, the threaded spindle rotates minimizing the oscillations due to concentricity errors. For a proper operation it is necessary for the user to provide solutions able to keep the spindle and the lead nut aligned. The guides can be external or directly implicate the structure of the lead nut, as can be seen in the following drawings.

AXIAL BACKLASH
In B the axial backlash between the threaded spindle and its support nut (either a worm wheel or a lead nut) is caused by the natural and necessary tolerance characterizing this kind of couplings. For construction purposes it is only important in the case where the load changes its direction of application. For applications where there can be reciprocating traction and compression loads, and therefore a need to compensate the axial backlash, it is possible to apply a backlash reduction system. The axial backlash reduction must not be forced in any case, in order to avoid that the screw and the support nut get blocked.