What are the characteristics of the ball spline?

The ball spline is essentially a linear bushing and shaft system,with axial grooves along both the shaft and the inside diameter of the nut.The load-carrying balls recirculates within the nut in much the same manner as the linear bushing.However,grooves in the shaft prevent rotation and facilitate torque transfer.This allows the ball spline to withstand overhung loads and moment loads,unlike linear bushings which can only support radial loads.

The ball splines along the length of the shaft and the inner surface of the nut contain grooves to resist rotation and transfer torque.

Because the ball splines are designed to have a much larger contact area between the ball and groove than standard bushings,the ball splines have significantly higher load capacity.Ball splines usually have two,three,or four grooves,although some designs have up to six.As with the raceways of profiled rail bearings,the grooves in the ball splines can be designed as circular geometry,providing two points of contact on each ball,or as Gothic arch geometry,providing four points of contact on each ball.

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Gothic arch geometries provide higher stiffness but also improve friction,while circular arc geometries have lower friction and smoother running characteristics.Torque capacity is determined by the number of contact points,so a ball spline with four Gothic arch grooves will have 16 contact points and deliver more torque than a ball spline with two arch grooves,with only eight contact points.

ALM provides custom service,ball spline can be manufactured according to custom's requirement.

The selection of ball splines combine the technical considerations of linear recirculating bearings and ball screws.Life is calculated using standard bearing life equations,using radial and torque loads.Like profiled guides,ball splines can be preloaded to increase rigidity and provide better support for torque loads.

The ball splines are fixed by rotating bearings,much like ball screws,and the end fixation(fixed-fixed,fixed-floating,etc.)plays an important role in determining the critical velocity,as does the shaft root diameter and unsupported length.Accuracy grades are also similar to ball screws,based on radial runout and verticality of the shaft end,radial runout of the nut body,and verticality of the nut flange,if applicable.However,ball spline accuracy grades are not based on industry standards such as DIN or JIS.

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