Machine Jacks Screw

What is a Machine Jack Screw

In machine design there is often a need to add linear movement to the assembly. You could always design a custom linear movement mechanism for your application, but is that always necessary? It is very useful to have a standard component that you can just add to your design. That component is a machine jack screw.

 

Image Credit: http://www.nookindustries.com/

 

Machine Jack Screw working principle

Machine screw jacks are mechanisms designed to add precise linear movement to the machine. Actually it’s a mechanism that transforms the rotary into linear movement. The mechanism consist out of wormgear assembly in the input section and a linear screw that is on the output section. This wormgear-screw assembly is also a speed reducer and a toque multiplier.  They can be operated by a hand wheel or a motor which is great for automation purposes.

Image Credit: http://joycedayton.com/

 

Loads on a machine jack screw

It is important that for every machine component you understand what kind of loads it is designed to handle. This is the most important information when implementing a component into your machine. Machine jack screw are designed to handle compression or tension loads as shown in the picture bellow.

Jack Screw acceptable loads

Jack Screw acceptable loads Image Credit: http://www.nookindustries.com

Machine jack screws that are under tension load can carry the entire rated capacity of the jack screw. The ones that are under compression loads do not. In the machine jack screws that are under compression loads the column load must also be taken into the consideration. This reduces the carrying capacity significantly.



Overturning loads and side loads are not acceptable. These loads will likely prevent the proper operation of the mechanism and reduce the working life.

Unacceptable loads on a machine screw jack

Unacceptable loads on a machine screw jack Image Credit: http://www.nookindustries.com

Considering the loads that these mechanisms are designed to handle loads only in the axial direction it is wise to provide linear guides with them. Guides will eliminate the influence of other loads on the jack screw and provide a safe and reliable working environment.

Uses and applications

Machine jack screws can be used as a single unit or in combination with more jack screw together. As mentioned before, when using a single machine screw jack you should add linear guides. Linear guides should eliminate the influence of all forces other then the ones acting in the axial direction on the machine jack screw.

Linear guides example

Linear guides

For added stability and increased load carrying capacity more machine jack screws can be connected together and to a single power source in order to make unison movement. Some examples of movement configurations are shown in the picture bellow.

machine jack screw configurations

Image Credit: nosenjack.com

Connecting jack screws together and with a motor is done with shaft couplings. These can provide a quick disconnection point and easy assembly.



Jack screw with shaft collar

Image Credit: nosenjack.com


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