Machine Design

Software for designing springs

Many small mechanisms contain a spring or two.

The input window for a beam spring shows the range of selections. It's useful to have the input matrix on screen when filling in the blanks.

The input matrix for cantilevered beam springs shows what is needed (Xs) and what is optional for different design conditions.

Variable inputs for a compression spring appear in the window to the right. Outputs are in the fields on the left. Definitions of spring variables with descriptive images would be a useful addition to the input window.

Ballpoint pens, for example, use coil springs while battery holders rely on beam springs for contacts. When the need for a spring arise, users can pick a reasonable fit from a catalog, or design the perfect one using software such as SpringCAD. The software handles all calculations for designing several varieties of beam, compression, extension, helical torsion, and solidtorsion springs.

Designing a spring involves a bit more than just running through an equation, so it takes a few minutes to learn and properly coordinate the various windows associated with each type of spring. Nevertheless, the software operates much like you'd expect: pick a spring type, fill in a few design values, select a material, and hit Calculate. The software crunches through its equations for the remaining values and then some.

There is a little more to it than that, however, because the program presents several options. For instance, beam springs can be cantilevered or supported at the ends, and the beam could be curved. The software also allows several different cross sections. Spring life is another selection. Springs can be sized for light duty (less than 50,000 cycles), medium duty, or heavy duty (500,000 cycles and up).

To avoid over or underconstraining designs, the developer includes a table or input matrix that identifies required and optional information. Starting with the table may be the best way to work. Decide what you don't know and find those empty slots in the matrix, select that matrix column for the solver (each is numbered), and type in known values.

When users under or overconstrain a design, the software lets you know it cannot proceed. Figuring out what information is extra or unsupplied takes a little study. Users might also design a spring with marginal quality. The software warns of that, too. For example, one coil spring I designed had an index outside the acceptable range of 4 to 16. The index for a coil spring is the ratio of maximum deflection over the solid height. An index of 7 to 12 is ideal.

The Help section is sufficient to pass for a short class on spring design. It defines variables for each spring and outlines a few design guides.

The software is not difficult to use, but it could be improved. For instance, variables on the input matrix are not in the same order as they are on the input screen. In the input matrix, wire diameter is the top line, while length is the first item in the input parameters. The same order in the two columns would take a few minutes off the learning curve.

The $295 package and a free demo version comes from Bare Hill Software Inc., 262 East Lake Rd., Rushville, NY 14544 (585) 554-5451, (

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