Tensioning a Ballscrew

For eliminating loss of accuracy due to thermal expansion, the ballscrew can be held under tension. In this case the lead error can be specified as negative 1) . Bearings must be selected accordingly. Steinmeyer will provide you with calculations regarding correct selection of bearings and resulting axial stiffness upon request.

The elongation due to pretensioning must be greater than or equal to the thermal expansion that would occur under the maximum temperature increase expected.

The pretensioning force must be considered carefully, as it will affect load capacity evaluations for the support bearings.

F_T = Screw pretension force [N]
E = Young´s modulus [210.000 N/mm2]
= Extension
l_p = Elongation [mm]
l_s = Length of unsupported shaft [mm]
A = Screw cross section [mm2]

The thermal expansion (l_T) can be defined as follows:

= Coefficient of thermal expansion [11,5 o 10^-6 / °C]
l_o = Overall length of screw [mm]
_t = Temperature gradient [°C]