We can use Hooke’s Law to help extrapolate how a new spring design will function, based on existing test data. Hooke’s Law is:

F = ky

Where F is the elastic force exerted by the spring, y is the change in length of the spring, and k is the “force constant” of the spring.

For example we can say that a spring with half as many turns will require twice the force to stretch the same amount.

The test data needed is the following:

Length of the coil spring – along the main axis of the spring

Number of coils in the spring – number of loops around the axis of the spring

Diameter of the coil – the diameter of a loop

Diameter of the spring material – thickness of round coil material

Force test data:

Change in length – 5mm

Force applied – e.g. 8 ounces

For example I see that there is a spring in the whoosh machine in the following tutorial:

http://www.shapeways.com/tutorials/designing_mechanical_part s_3d_printing_the_whoosh

The following information would need to be filled in:

Length of spring – e.g. 15mm

Number of coils – e.g. 7

Diameter of the coil – e.g. 10mm

Diameter of spring material – e.g. 1mm

A simple test could be done to get the force data:

Add weights to the top of the button until the top of the button is pushed down so it is flush with the top of the surface it is sticking up through, e.g. 8 ounces of weight. Then measure the length of the button that sticks above this surface with the weigh removed. This is the change in length y.

Tests can also be done by stretching the spring. I think the constant k should be the same for stretching and compressing. Tie a weight to the end of the spring and measure how much it stretches by, e.g. if it starts out 15mm and stretches to 18mm, then y is 3mm here. The force is the weight used.

It would be good to have test data for different diameters of spring material, e.g. 1mm, 2mm, 2.5mm etc.

I think some extrapolation could be done for springs of the same spring material diameter, but different coil diameter, by using the overall length of the coil material, i.e. the length of the coil material if you uncoiled it into a straight line.

Please add your data to this thread for any designs that you have done. After some data is gather some tables can be put together to go in the thread.

Thanks

Steve W.

]]>

We can expect to get the same amount of deflection, for the same amount of force (weight ) if we take this beam and wrap it into a spiral shape to make a coil ( via the magic of CAD or Blender ).

Steve]]>