Max Safe Travel and Springs Taking a Set
Elastic Limit = Maximum Safe Deflection A.K.A Maximum Safe Travel
The terms “maximum safe travel”, “elastic limit,” and “taking a set” can be a little confusing to understand because they are all related. These terms are all important in regards to the limits of deflection that each spring has. That is why you may also hear the term “maximum deflection” which can sometimes be used interchangeably for “maximum safe travel”
As you may know, springs can only be compressed, extended, or torqued to a certain point before they break or fail. Since each spring design is different, it is very necessary that you are well aware of the limits that each specific spring has.
The elastic limit of a spring (a.k.a maximum safe travel) is the distance a spring can safely compress, extend or torque. If the spring is pushed past this limit it "takes a set." Elastic Limit and Maximum Safe Travel are synonyms, both refer to how far a spring can go safely, without suffering damage.
Taking a Set: When Springs are Forced Too Far
Taking a set is when a spring is forced to the point of no return and suffers permanent damage. Once a spring takes a set it will never be the same because it has been force to withstand a load that it past its capacity. When a spring "takes a set" it means its resilience and structure has been affected and can no longer recuperate the initial free/unloaded length (or torqued position in the case of torsion springs). This happens because it has been compressed, extended or torqued past its limit.
To better understand this let's use a more tactical example. Humans have certain resilience and every person has different amount of flexibility. If you pull your finger too hard it can become dislocated, if you bend your arm back too far it can break, we all have a different elastic limit. Some of us are not flexible at all while other are incredibly flexible and can withstand a deeper bend or a farther twist. That is why we need to know our limits and stop at the "safe point" of our bodies where we can withstand some sort of twist, bed or stretch. That "safe point" before we get hurt is what the spring's "max safe travel" or "max safe deflection" is.
How Far Can Your Spring Go?
Let's say a compression spring's free length is 1 inch and, based on how thick the coils are, you can physically compress it down to the solid height of 0.25 inches. Does this mean you should? Maybe. It depends. If the spring’s maximum safe travel is 0.75 inches it means you can make the spring travel down all the way to 0.25 inches without any problem. However, if the spring’s maximum safe travel is 0.6 inches, you will only be able to safely compress it down to a loaded height of 0.4 inches without it taking a set or taking a set.
Let me put it this way: if you should ignore a spring's maximum safe travel and press down a compression spring past this elastic limit, it might go down, but it would have endured so much pressure that it will take set.
Knowing the Load Your Spring Can Handle
Can your spring handle the load you will place on it? How do you know? The answer is easy. All you need to do is go into our Spring Creator calculator and input the measurements of the spring, it will automatically give you an analysis of the spring. In the analysis, go to the section of “rates and loads” and look at “maximum safe travel considering solid height”. You need to respect this value if you want your spring to work right and have a longer cyclic life.