Coiled spring pins provide design solution for circular saw

16 April 2012

The use of standard duty coiled pins as hinge pins in a circular saw blade guard application was causing problems during manufacture due to the excessively high insertion forces. Following design advice provided by Spirol Industries, coiled spring pins, which have only half the exertion force, are now being used instead.

Different assembly lines were being used to install the coiled pin and all the insertion problems were being experienced on the fully automated line that had less than half of the insertion force of the semi-automated line. Based on empirically derived insertion data for the coiled pin, the automated line had a cylinder that was undersized for this application.

When Spirol were asked to come up with an improved design solution, no shear strength requirements for the coiled pin were supplied for this application. A simple option, which would require no changes to the automation equipment or the hole sizes in the components, was to change to a light duty coiled spring pin. The insertion force for the same coiled pin in light duty was approximately half that of the standard duty pin in the same application.

There were other recommendations made by Spirol. For example, the customer was using a tapered disappearing pin to align the holes and there was a tendency for the top holes to be misaligned due to the severe taper. The diameter of this alignment pin needed to be the same for its entire length.

The insertion quill also had slightly rounded edges. The quill was smaller than the diameter of the coiled pin and was therefore pressing on the inner coils, thereby increasing the insertion force. Spirol also stressed the importance for the assembly be supported/clamped to limit the cantilever lifting action during insertion.