How to Utilize Vulcan’s Stock Constant Torque Springs

Vulcan Spring has just introduced a line of stock constant torque springs.  We call this our Contorque® spring.  In this blog, we will give some details on how to use these springs in your design.  Contorque® springs have been discussed in previous blogs, so this blog will focus on the installation and use of the spring once it has been received.

Reverse Winding

The first noticeable feature is that the scallop end detail is on the innermost coil of the spring.  Manufacturing the spring in this configuration allows for what is called reverse mounting.  The scallop will eventually be attached to the output spool.  Vulcan Spring coils with the scallop end on the inside so that the straight cut outer end of the spring can be wound directly onto the storage spool.  If this spring is to be housed in a cavity it is still necessary to reverse the spring, making the outside the new inside.  Once wound onto the storage spool, or onto itself, the scallop end will be on the outside and ready to attach to the output spool.  The spring does not need to be fixed to the storage spool.  If the recommended storage spool diameter is used, the spring will wrap tightly on the spool during reversing.

Pickup End

After reversing, there will be little or no uncoiled material pickup on the outer end because the spring was manufactured for reverse mounting.  This allows maximum constant force throughout the number of available turns.  The end should be carefully attached to prevent any bumps or creases in the spring.

Attaching the Scallop

There are many ways the scallop can be attached to the output spool.  The easiest way is to make an oblong slot in the spool.  The slot length should be longer than the width of the spring material and the width should be greater than the width of the inside portion of the scallop but not as wide as the spring material.  The spring is inserted into the slot and turned into place.   If necessary, a hole may be punched in the end to use a fastener instead of the scallop.


It will be necessary to pre-wind the spring prior to usage.  This pre-wind should be 1–2 turns and will not detract from the number of turns listed on the specification sheet for each spring we offer.  In use, the spool should not be allowed to rotate back past this point of pre-wind.  If the output spool is allowed to completely unwind the spring can be damaged and will not function correctly.

Torque Profile

While these springs are called constant torque, there is a slight increase in the torque throughout winding or extension.   During manufacture, the torque is measured halfway through the total number of turns to provide the proper force throughout the rotation.  If there is a cable winding on the output spool, the force on the cable can increase as the diameter of the spooled cable decreases.

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