Screw Thread Accuracy Screw jacks using trapezoidal rolled leadscrews have a lead error of around 0.10mm over 300mm of thread but the use of optional whirled screw threads can reduce this down to around 0.05mm. It is possible to attain even lower pitch error via use of ballscrews as opposed to leadscrews and can yield an accuracy of 0.023mm and lower over 300mm – please contact of sales team for information on what options we offer. Tolerances 6 TEL: 01827 288122 sales@wmh-trans.co.uk FAX: 01827 253390 www.wmh-trans.co.uk Axial Play – “a” Axial Play has no influence on positioning accuracy when loading of the jack is in one direction only (i.e. in constant compression or in constant tension) as the load is always thrust upon one flank of the screw thread only. Operating Temperature Screw jacks with standard lubrication have a rated working temperature range of -10 °C to +40 °C but special lubricants are available to increase this range to -30 °C to + 80 °C Radial Play – “b” Radial play occurs only in the case of type 1 (travelling screw) jacks as a result of clearance between the outer diameter of the screw thread and the guide ring within the jack body. This clearance is typically around 0.2mm and results in radial play “b” proportional to the stroke length. The use of whirled as opposed to rolled screw threads will help to reduce this clearance but it can never be fully removed as to allow for proper lubrication and thermal expansion. Although screw jacks have been designed to account for a small amount of radial play, they are not designed to withstand any loads that do not act parallel to the axis of the screw – this applies to both type 1 (travelling screw) and type 2 (travelling nut) screw jacks. WMH recommends the use of external guidance in all applications to remove any possible side loads from the screw jack which would otherwise lead to premature wear and failure – please contact our sales team for information on the range of linear guidance systems available from our stock. Tooth Play – “backlash” Tooth profile play or “backlash” is a result of clearance between drive and driven teeth of the worm and wheel within the jack body. This clearance is necessary to allow for thermal expansion and correct lubrication of the mating parts to prevent binding and premature wear or failure. When new, this backlash is around 0.10 – 0.30mm and varies on the size of the components but will increase over the service life of the jack.