How to achieve long travel and high speed with ball screws
From the equation, you can see that the critical speed and unsupported length have an inverse square relationship. Put simply, by halving the unsupported length, the critical speed increases by a factor of four. Therefore, the most effective method to increase the critical speed is to reduce the unsupported length. But how can you reduce the unsupported length of the ball screw without sacrificing the travelВ length?
Long Travel vs. High Speed: В You Can Have Both
Ball screw supports can solve this length-speed dilemma. These floating supports (typically used in sets of 2, 4, or 6) are located on each side of the ball nut, and are connected in a way that allows them to extend to an equal spacing on one side of the ball nut, as the nut travels in the opposite direction, reducing the unsupported length proportionally. In the direction that the ball nut is traveling, the supports stack up at the end of the screw to provide the least interference with the stroke.
Based on the critical speed equation, adding just one set of ball screw supports (one support on each side of the ball nut) will quadruple the screw’s critical speed!Cutting, routing, and other operations in metal manufacturing and woodworking are the most common applications for ball screw supports, due to their need for high thrust forces and good positioning accuracy while moving long distances at fast speeds.
It is important to remember that ball screw supports require additional space, and to calculate the length of the screw accordingly so the desired travel length can be achieved. Each ball screw support typically adds three to five inches of “unusable” length, so one set of supports increases the screw length by six to ten inches. This also negates a small amountВ of the reduction in unsupported length, but the addition of screw supports will rarely have an adverse affect on the final ball screw selection. In some cases, the use of ball screw supports will allow you to select a smaller diameter ball screw and reduce the requirements on other parts of the system, such asВ В couplings, bearings, or motor-drive components.
When your application requires high thrust forces, high positioning accuracy, or contamination protection, but the limitations ofВ length and speed seem to exclude ball screws as a suitable solution, talk to your screw manufacturer or machine builder about adding ball screw supports to the assembly. They could help you avoid the length-speed compromise.