This is part of the series of 30 exercises developed during the E3D+VET program. The aim of this Erasmus+ program is the immersion in 3D printing of VET centres (website: ). The model assembled pieces is composed of two parts that were printed out separately. In this exercise there will be three types introduced. All types show a repeating pattern, which, once assembled, seems to create an inseparable joinery. These models are grounded on the well-known lock and key concept and the clearance between the two parts should allow for the parts to slide in a smooth way. 1. Dovetail: This model’s basic geometry is a cube and it is made up of two halves. One half has two protrusions which are formed like the classic dovetail in carpentry (but distorted). The other half has two cavities which are formed like the dovetail too. These two halves create a connection, that can only be loosened by pushing the two parts in the right directions. There is only one possible axis that allows movement (forwards and backward, hence two directions). This axis is in parallel to the axis along which the cavities and the protrusions are oriented and constructed. 2. Pentagon: This model is a variation on the Dovetail. Here the two halves show a pentagonal form, and apart from that it follows the same construction principles as the Dovetail. 3. Triangular Dovetail: The two halves form an equilateral triangular that can only be loosened by rotating the triangle and then pulling the parts apart. Here the pattern is rotated around the z-axis and intersected with the triangular body.