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What is an Actuator?

Posted 28th April 2016

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The raw definition of an actuator is that it is a mechanism that puts something into automatic action.


In our line of business the actuators we commonly come across are rotary actuators which are used on lathes, however actuators are not limited to lathes.  I will focus on the rotary type that you will come across more frequently.  The rotary actuator on a lathe is the device mounted on the back end of the spindle outside of the work area.  It is responsible for the holding force which closes the jaws on the chuck which holds the part being machined by the lathe. 


The rotary actuator is a hydraulic cylinder on which the center shaft can move back with hydraulic force as it holds that force while the inner shaft spins. The actuator does not spin on its own, but is threaded onto the spindle draw tube of the lathe. When the spindle runs, the actuator shaft spins, while the outer housing of the actuator is held in a stationary position by a bracket which is usually mounted to the frame of the lathe.  There will be typically three hose lines which run to the actuator.  Two lines which handle the extend and retract movements, and one line for an oil drain path.  The spindle shaft they connect to is commonly called the spindle draw tube and it goes through the center of the spindle and connects to the back of the chuck.  The actuator extending and retracting action controls the jaws of the chuck of which the body of the chuck is mounted to the spindle.  This motion causes the jaws to either move in, or to move outward.  The jaws are typically designed so you can move them in to clamp on the outside of a part, or to move them out to clamp a hollow part from the inside.  


I mentioned a drain line earlier.  This drain line is usually a larger clear inner braided hose so you can visually see the oil flow down and it typically runs to a drain port on your hydraulic system which controls the actuator.  I mention that because there are many times when people call for hydraulic units, but don’t need a hydraulic unit.  They think they do because they may have a bad leak in the actuator.  You see, the actuator is meant to allow some oil flow over the bearings to allow free movement at high speeds.  This oil cools and lubricates the moving parts allowing the outside to be stationary while the inside can spin at 5,000 rpm, as an example.  When you have seal failures in the actuator the oil trickle becomes a large flow of oil.  When this occurs the pump may run hot, or may lose holding force on the chuck as an example.  So this will appear as a hydraulic unit failure, but is not.  You will need to advise them of what they should check first. 


So when you have someone ask you about a hydraulic unit, because they think that they have a failure, you need to ask if it is a lathe and then ask if they checked to see if they have a large leakage from the actuator.  If you don’t do this, and they put a new pump on that they bought from you and it does not work, then they will lose confidence in your knowledge of the products.  So, always try to advise the customer and help them to learn from you.  If you do this, then they will trust that you are knowledgeable and will feel more comfortable calling again to help them solve future problems that come up.  Now you should have some idea of what a rotary actuator is on a lathe and how it pertains to you.
 

Written By: Darrell Janesak, Senior Technology Advisor

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