This project consisted in creating a secateurs design primarily following ergonomic criteria. To achieve this, a number of user trials were performed, that resulted in substantial changes to the design.

User testing

Multiple prototypes and mock-ups were made, ranging from scale cardboard models to more functional ones designed to test the ergonomics. Finally, a model was made that should represent as closely as possible the final product in aesthetics and function.

After testing the product, users were requested to fill out a questionnaire to help refine the design.

View user trialing questionnaire 

The chosen design uses its geometrical configuration to achieve a large reduction in the force required to operate in comparison to the sample of over 30 products on the market that were benchmarked.

This is the result of maximising the par conversion and minimizing the distance that the fingers need to grasp in the open position. An over reduction of this space resulted in possible pinching in the first crude prototype. Subsequently the handle form was modified and the distance increased to insure smooth operation without any pinching or discomfort.

In the following images you can see the difference between the first user trialing model and the final design.

First secateurs model made from acrylic and foam. Spring inside is from a door handle.

Final design. Substantial changes can be appreciated...

After observing secateurs use it was also decided that the ergonomic testing must be done both with and without gloves.

Prototype creation

The design detailing was first created manually with pencil and paper. Modelling the pre-defined design in SolidWorks proved a gratifying challenge as this was my first SolidWorks creation. The organic forms of the handle were created with a series of loft functions as the cross sections had been defined previously using anthropometric data from the hand.

By using 3D CAD software it was much easier to ensure there were no conflicts in the inner working and that the opening angle was adequate, as the spring is contained within the design. Disassembly and durability are ensured with the use of spring stoppers.

Rendering images of the CAD model...

Exploded view showing the inner components and assembly.

It was decided that the prototype should be made of layers of laser cut acrylic. To ensure accuracy, a second CAD model was created from the first, but consisting in extruded layers. These were then exported to files used for laser cutting.

Checking that all the layers are there in the workshop. The left images show pics of the CAD file created to aid assembly of the laser cut acrylic layers.

After gluing the layers together, they were manually sanded down to obtain the curved form necessary for the handle. Imperfections were filled in and sanded again. In the following image the prototype is placed over the original hand drawn files to show how closely the profile corresponds.

This image shows the physical prototype (under construction) placed over the original drawings used to model it. Axle, spring and blades have yet to be assembled.

Finally, the model was spay painted and assembled. The spring, axle and stoppers were custom made from bits and pieces lying around the workshop and a fully functional model was obtained that very closely resembled what the final product might look like.

Ready to paint...