Instead of the worm drive systems discussed here, a bevel gear system could be used to convert rotation to linear movement. This would offer greater effectiveness to a machine screw jack due to it producing a rolling contact instead of the sliding contact of worm drive elements. It could, nevertheless, come at a greater initial cost and will not cover as greater ratio range as worm drives.
Also called power screws, lead screws include a number of different types of thread profile which are ideal for different applications. Acme lead screws are described by their trapezoidal thread profile and 29° flank angle and are commonly within American Imperial machine screw jacks. An alternative to the Acme business lead screw in a machine screw jack will be a square lead screw.
European or other international screw jacks utilise a trapezoidal lead screw with a 30° flank angle and complies to an ISO metric standard.
Ball screw jacks require the thread of the business lead screw to get a profile which allows for the travel of the balls. To improve load distribution and minimise use, the ball screw track has a gothic arch profile.
Recognition of the trapezoidal screw thread comes from the fact that it’s easier to machine and is therefore less expensive than sq . and ball screw thread forms. Additionally, because of the large region of contact between the business lead screw threads and the worm wheel, there is usually a sizable load carrying capability. This outcomes in high friction which is harmful to efficiency but does mean the system is much more likely to be self-locking. This low performance means that this kind of screw jacks are more suited to noncontinuous or intermittent operation.
Many applications do not warrant the extra expenditure of a ball screw jack since they do not require continual drive. In configuring a screw jack a prediction is made from the frequency of actuation and this will stage to the appropriate screw jack to end up being selected.
Translating Design Jacks are most often selected. With this style, a driven insight worm functions on an internal worm gear causing the lifting screw to extend or retract. Operation requires that rotation of the lifting screw be avoided. This rotation it restrained whenever several jacks are linked with the same load.
Keyed Design Jacks are utilized any moment rotation of the lifting screw isn’t restrained. For instance, when you must lift the jack to meet up a load. This is how they work: An integral, set to the jack housing and inserted into a keyway milled in to the length of the lifting screw forces the lifting screw to translate without rotating.
Keyed For Travelign Nut Design Jacks (KFTN) are another choice. These jacks have a fixed size lifting screw that rotates. Loads are attached to a flanged “traveling” nut that translates along the space of the rotating screw. This type of jack is perfect for applications that cannot support a screw protection tube or that want a flush mount
The worm wheel acts on the ball screw (via the ball nut) which actuates the lead screw. This technique offers greater performance between the input and the useful output compared with a machine screw jack. Furthermore, it allows for greater actuation speeds and, due to the low friction, is quite durable. However a ball screw jack isn’t inherently self-locking and, because of its improved precision components, the original outlay is better. The resulting improved efficiency however implies this is often offset against smaller sized drive train elements and a significant reduction in the necessary power.