• Wire Diameter: The diameter of the spring wire from one side of the wire to the adjacent side of the wire. 

• Outer Diameter: The outside diameter of a compression spring from one side of the outer diameter to the adjacent side of the outer diameter.

• Mean Coil Diameter: The average of measurements from outer diameter to inner diameter. The best method to calculate for mean diameter is either subtract one wire diameter from the outer diameter or add one wire diameter to the inner diameter. This will give you the “Mean Coil Diameter” of the spring. Mean coil diameter is used to calculate the spring rate and the stress of a compression spring. 

• Inner Diameter: The Inside diameter of a compression spring from inside one side of the inner diameter to the adjacent side of the inner diameter.

• Free Length: The length of a compression spring in a free uncompressed state also known as spring length or overall spring length. 

• Total coils: The total amount of helical wound coils that contain pitch and have no pitch in a compression spring, meaning all coils in a spring. 

• Active Coils: The amount of helically wound coils that contain pitch to exert energy when a spring is compressed. 

• Solid Height: Solid height for compression springs is defined as the point at which all wires in your spring are touching and no more force can be exerted by the spring. Also known as coil bind height where all spring coils are in contact with each other and the spring cannot compress further.

• Compression Spring Rate Definition: Spring rate k or spring constant is the proportion of a spring’s force in (pounds or newtons) to one unit of travel (inch or millimeter). It is a constant force value which helps you calculate how much load you will need with a specific distance of compression travel and it will also help you calculate how much compression travel you will achieve with a certain load force.

• Closed and Squared Ends: This configuration provides a flat surface without grinding and is best suited for springs with a slenderness ratio of less than 3.5. Closed and squared ends offer stability and reduce the likelihood of falling over under load. Suitable for applications where the compression spring's slenderness ratio is less than 3.5 and is required to stand up vertically straight without support.

• Closed and Ground Ends: By grinding the ends of the spring, a more precise and flat surface is achieved, allowing for better contact with the load. This end type is preferred for high-precision applications requiring uniform load compression and is often used in manufacturing and automotive industries. Closed and ground ends are recommended for springs with a slenderness ratio greater than 4.

• Open Ends: Springs with open ends are not modified after coiling, resulting in a natural, slightly uneven end. The advantage of open ends is that one can obtain more travel since open ends have no dead coils on each end thus freeing up solid height space to provide more travel. This option is suitable for applications where end precision is not critical, offering a cost-effective solution without sacrificing performance.

• Double Closed Ends: A specialized option where both ends of the spring are closed but not ground, offering enhanced vertical stability and resistance to lateral forces. This end type is particularly useful in applications requiring the spring to align with minimal guidance. Double ends take up more solid height but the payoff is stability.

• Triple or more closed ends: A custom hybrid option that has many advantages: An option for fine wire diameter springs of .005 to .025 thousand of an inch. Where  compression springs that have a fine wire diameter and large spring index need extra stability when compressing the spring.

• An option for having multiple closed ends on one side of the spring for threading the springs inner diameter over a threaded bolt or threaded shaft. Multiple closed ends offer a way to secure and assemble a spring over a thread. The springs wire diameter must synchronize with the thread size as well as the compression springs inner diameter must coincide with the bolts outer diameter for proper fit.

• One Closed End and Multiple Closed Ends:  An option for having one closed end and multiple closed ends on the other side of the compression spring. This end type offers stability on the base of the spring as well as a closed end on the top of the spring.  This end type can be ground for a more precise flat surface offering superior stability.

1. Compression Spring Wire Material: Spring tempered wire is used in all coil compression springs. This wire is spring tempered and has a rockwell hardness factor of between C41-60. There is an ample gamut of spring material varieties listed below.

• Music Wire (ASTM A228): Renowned for its high tensile strength and robustness, music wire is the go-to choice for springs requiring high load capacities and fatigue resistance. Ideal for applications demanding acute precision and strength.

• Stainless Steel 302: Offers excellent corrosion resistance and is used in applications where the spring is exposed to corrosive environments. Its durability and longevity make it suitable for food industry machinery, medical devices, and marine applications.

• Hard Drawn (ASTM A227): A cost-effective option, hard drawn wire is used in applications where material strength is crucial, but exposure to corrosive elements is minimal. Commonly found in commercial products and industrial machinery.

• Other Materials: For specialized applications, Acxess Spring also offers springs in exotic materials such as Beryllium Copper, Phosphor Bronze, Chrome Silicon and more, here is a listing of all the unique properties of popular spring materials to meet specific environmental and operational demands.

• Zinc Plating: Matt chrome in color, offers excellent corrosion resistance, making it a popular choice for springs used in outdoor or humid environments. Zinc plating also provides a clean, bright appearance and additional protection against rust. 

• Black Zinc: Black in color offers good corrosion resistance, making it a good choice for springs used in outdoor environments. Black zinc plating also provides a clean appearance and additional  rust protection. (Lalo Show Icon)

• Black Oxide: Black matt in color, primarily used for aesthetic purposes or to minimize light reflection, black oxide also offers mild corrosion resistance and reduces friction between coils, making it ideal for applications requiring a sleek appearance without extensive exposure to corrosive elements. 

• Gold Iridite: Provides superior corrosion resistance and electrical conductivity, making it an excellent choice for electronic components. The gold iridite finish is often used in electrical connectors and high-reliability applications where performance cannot be compromised.

• Nickel Plating: Offers a lustrous shiny silver chrome appearance and is electrically conductive. This bright glossy chrome finish is aesthetically appealing. 

• Copper Plating: Copper in color is primarily used for springs that need to be conductive, great for springs that go into battery or electrical contacts. 

• Gold Plating: 14K Gold Electroplating is used for high electrical conductivity compression springs. This plating requires placing the compression springs on a copper wire necklace or placing the springs individually on a rack to perform the gold electroplating more costly but greater conductivity.

Measuring a compression spring accurately is crucial for its performance and compatibility with your application. Key dimensions and how to measure a compression spring include:

• Wire Diameter: To measure the wire diameter (WD): Place the lower jaws around the springs wire diameter as shown in the picture then slowly push the jaws of the caliper so that the two parts of the lower jaws touch the wire diameter.

Hint:  You can also lay the spring down and place the lower jaws of the caliper around the wire diameter to get an accurate measurement.

• Outer Diameter (OD) To measure the outer diameter of a compression spring use a digital caliper (as shown). Measure at one side of its widest outside point then measure the other side from its widest outside opposite point to get the correct outside diameter of the compression spring.

• Inner Diameter (ID): Insert the upper jaws of the digital caliper into the inside diameter of the spring making sure to measure the largest part of the ID. Make sure to rotate your spring slowly with one hand and with the other pull the thumb screw outward so that the upper jaws get an accurate measurement. (Lalo Show picture)
   

Hint: Hold the spring vertically straight so that the upper jaws go into the inside diameter, and make sure the tip of the spring coil is at high noon or 12 O`clock.  then rotate the spring a bit to the left then to the right as you pull the thumb screw. You will feel the larger part of the spring’s inner diameter that's the  measurement you want. 

• Free Length: How to measure the free length of compression springs (FL) :
  Hold your compression spring horizontally straight as shown then insert the lower jaws around the length of the spring making sure to measure the entire vertical  length of the spring.   

• Total Coils (TC): How to count total coils in a compression spring:
  Hold your spring as shown in the picture to the left. Start counting on the second wire which is the first complete coil then count all the coils until the last coil. This spring has 8 total coils. 

• Active Coils (AC): How to count active coils in a compression spring. 
  Active coils are the coils that have pitch in between the coils (also known as open wound coils). This spring has 8 total coils but since the first and last coils are closed we cannot consider them active coils  therefore we subtract the 2 closed coils and we get 6 Active coils with pitch. 

• Solid Height: Calculating Solid Height - Closed And Square Ends:
  The formula for calculating solid height on closed and square ends is:
  Total Wires = Total Coils + 1 
  Solid Height = Total Wire * Wire Diameter 

Spring compression, or how much a spring compresses under a given load, can be derived from the spring constant and the applied load using Hooke’s Law:

F=kx

Rearranging for compression (x) gives:

x=F/k

Using the maximum load of 25 lbs and the spring rate of 20.022 lbs/in:

X = 25/20.022 ≈ 1.249 inches of spring compression or deflection

This simple equation shows the compression spring’s capacity to compress 1.249 inches under a load of 25 lbs without exceeding its elastic limit of 1.561 inches.

Example is based on Part Number PC072-600-15100-MW-2750-CG-N-IN

This calculation provides a foundation for understanding the spring's behavior, enabling the selection or design of springs that align perfectly with the operational demands of the application. Acxess Spring’s Spring Creator 5.0 simplifies this process by automating calculations, ensuring precision and efficiency in spring selection and design.

The spring constant (k), also known as the spring rate, indicates the spring's stiffness or spring rate of force. While Acxess Springs Spring Creator 5.0 provides the spring rate directly, let’s illustrate an example of how it could be theoretically calculated if we had started with basic dimensions and properties:

Given:

• Wire Diameter (d) = 0.043 inches
• Mean Coil Diameter (D) = Outer Diameter 0.390 - Wire Diameter 0.043 inches = 0.347 inches mean diameter
• Total Coils (N) = 8.250

The spring constant formula for a compression spring is:

k = Gd^4 ÷ (8D^3 * n)

Assuming a modulus of rigidity (G) for Stainless Steel 302 (which typically ranges around 11.2 x 10^6 psi), the calculation would detail the theoretical underpinnings of determining k, leading to the provided 16.282 lbs/in as a practical outcome.

Example based on Part Number: PC043-390-8250-SST-1000-CG-N-IN

Calculating the load on a spring is pivotal in the design process, involving the determination of the force required to compress the spring to a desired extent. This calculation is foundational, as the load directly influences the spring's dimensions and material selection to withstand operational forces. In technical terms, the load is often derived from the application's functional requirements—whether supporting the weight in a valve or absorbing shock in a suspension system. The calculation involves understanding the maximum forces the spring will encounter and ensuring the spring's design can accommodate this with an adequate safety margin.

Calculating the spring's maximum load capacity involves understanding the spring's design limitations and material properties. For a spring with a spring rate of 16.282 lbs/in and a maximum deflection of 0.604 inches, the maximum load capacity can be determined using the formula:

Maximum Spring Load = Spring Rate × Maximum Spring Deflection (Travel)

Plugging in the values:

9.837 lbs = 16.2820 lbs/in × 0.604 inches

This calculation indicates the highest force that can be safely applied to the spring without risking permanent deformation, based on its material (Stainless Steel 302 ASTM A 313) and design parameters.

Example based on Part Number: PC043-390-8250-SST-1000-CG-N-IN

Calculating a compression spring's loaded height or (compressed height) is opposite of calculating distance traveled. This involves determining the compressed height of a spring when subjected to a specific load of force. This is crucial for ensuring the compression spring fits within its operational environment when compressed. The calculation requires knowledge of the spring's uncompressed free length and its compression spring rate under load, often utilizing the formula:

Loaded Height = Free Length - (distance traveled or compression distance).

Accuracy in this calculation ensures that the spring will not only fit within the assembly at its working state, but also function as intended without undue stress or risk of bottoming out.

A spring with a free length of 1.000 inches and a maximum travel deflection of 0.604 inches under load is designed to compress within its maximum operational load limits of 9.834 lbs. With a spring rate of 16.282 lbs/in, calculating the loaded height involves subtracting the compression spring's travel from the free length: 1.000 inches − 0.300 inches (Travel) = 0.700 inches loaded height. This loaded height ensures that the spring, when compressed by the load of 4.885 lbs, will not exceed its max travel of 0.604 inches nor will it exceed its maximum spring load of 9.837 lbs, thus avoiding potential damage or failure.

Example based on Part Number: PC043-390-8250-SST-1000-CG-N-IN

Understanding the distinction between compression spring load and compression spring constant is essential for precision engineering. The spring load refers to the external force applied to compress the spring, which can vary depending on the application's requirements. It represents the operational demand of the spring. In contrast, the spring constant k is an intrinsic physical metallurgical property of the spring that indicates its stiffness or resistance to compression. Defined technically as the force required per unit of displacement (K = F/x), the spring constant is determined by the spring's material, outer diameter, wire diameter, and number of coils. Recognizing this difference allows engineers to design compression springs that are not only capable of handling the expected load but also exhibit the desired performance characteristics in terms of compression and energy absorption.

The difference between spring load and spring constant is exemplified by the specific dimensions of this spring. The spring load, capped at a maximum load of 9.834 lbs, is the force the spring is designed to withstand, influenced by its application requirements. In contrast, the spring constant k, or spring rate, of 16.282 lbs/in, signifies the spring's stiffness—how much force is needed to compress it by one inch of distance. This spring's design, with a wire diameter of 0.043 inches, total coils of 8.250, and closed and squared ground ends, directly influences its spring constant. The spring constant reflects the spring's inherent characteristics determined by its physical dimensions and material type and metallurgical makeup, distinct from the operational force or load it accommodates in use.

Example based on Part Number: PC043-390-8250-SST-1000-CG-N-IN