Defining the optimal dimensions

The first step of the design was to define the optimal dimensions of the double cap. This device presents two constraints :

The screw pitch adapted to the sample vials
The connector must pierce the aluminum seal after starting to screw

The first problem was solved by reverse engineering. We cut an existing cap in four to see the shape of the screw pitch and measure it with a caliper.

For the second one we measure the difference between the top of the screwed cap and the top of the vial to define the maximal height of the connector.

We finally take the biggest possible diameter for the connector, to reduce the Reynold number, i.e. allowing a better flow by reducing capillarity.

In the optics of making accessible for everyone the project, we realized the industrial drawing of the piece. It gives all the optimal dimensions of the double cap and especially of the connector. It had been realized with LibreCAD, which is a free and open source software.

We find in this drawing the dimensions of the connector part and of the double cap with a thickness of 1mm.