Compression Spring. Compression Spring Calculation and Drawing

Compression Spring (Pressure Spring)

One of the frequently used machine elements, the compression spring is also known as a pressure spring. In this article we’ll take a look at compression spring calculation, compression spring drawing, and the elements and formulas of compression springs.

On the market, compression springs are categorized as hard, medium-hard, or soft, based on the load they can carry without losing their properties, and spring manufacturers usually indicate these categories with colors. That is, springs are generally manufactured in different colors according to their hardness grade.

Helical compression springs with a round cross-section are made by winding round-section spring wire helically, hot or cold, around a mandrel.

The ends of these springs, which resist the compressive force, are optionally manufactured in generally 4 types: open or closed, unground or ground.

The figure below shows helical compression springs categorized by their end conditions.

Helical compression springs are generally made with closed ends. These sections are ground so the spring sits flush on its seat. This grinding covers roughly 3/4 of the coil diameter when viewed from above the spring.

The formulas for total number of coils, spring solid length, and free spring length, used in spring calculations and shown in the drawings based on the spring’s end conditions, are given in the table above.

Compression Spring Technical Drawing

In drawings, particularly in assembly drawings, helical compression springs should be shown in elevation as in figure (a) below, in section as in figure (b) below, and, when a symbolic representation is desired, as in (c). In these figures, even though the helix formed by the spring wire is actually a curve, these sections are drawn as straight lines. The shape and dimensions of this kind of spring are standardized in TS 1440.

If the spring’s wire diameter is too small to show hatching lines, it can be shown filled solid black. The symbolic representation should only be used when, due to lack of space, the spring cannot be drawn in elevation or section. Standard helical compression springs are specified by mean diameter (Dm), wire diameter (d), and free length (Lo). For example, a compression spring with Dm = 50mm, d = 4mm, Lo = 150mm is designated as “Compression Spring 50x4x150 TS 1440/1”.

The manufacturing drawing of a helical compression spring is given above. When drawing this type of spring, it isn’t necessary to draw every coil that makes up the spring. Only a few coils at the start and end are drawn, and the space between them is joined with centerlines.

The dimensions that need to be found in a compression spring drawing are as follows:

Outer diameter (Da) or inner diameter (Di) dimensions,
Mean diameter (Dm) dimension,
Free length of the spring (Lo),
Spring wire diameter (d),
Maximum deviation parallel to the axis (e1),
Maximum deviation perpendicular to the axis (e2),
Angular value of the seating surface (270° + 60°).

The following notes should also accompany the drawing:

Total number of coils (ig),
Number of active (working) coils (if),
Helix direction (right-hand or left-hand),
Length of the spring wire when uncoiled (L),
Pitch (h),
Load application frequency (n),
Spring material,
Max. operating temperature (t),
Mandrel diameter,
Hardening or coating processes, and any other surface treatments, if applicable,

Other special details:  
If needed, a force diagram of the spring is drawn, and the following dimensions are shown on it.

The spring’s operating force (P1) and its corresponding length (L1),
The permissible load (Pn) and its corresponding length (Ln),
Solid length, in other words the length at maximum compression (Lbl),
The sum of the smallest gaps between the active coils (Sa)