Link 1 turns about fixed axis A and is connected by turning pair B to slider 5 which, in turn, moves along the axis of link 4. Link 3 is connected by turning pair K to link 4 and slides in guide a of link 1. The axis of guide a is perpendicular to line BA. Roller 2 has a sharp-edged rim and rotates about the axis of link 4. When link 1 turns about axis A, roller 2, cutting into the surface of the drawing with its sharp edge, moves during each instant along the line of intersection of the planes of the drawing and of roller 2. The envelope of the successive positions of roller 2 is a spiral of Archimedes with the polar equation, with respect to pole A, ρ=b(ϕ+ ϕ₀) where b=A͞B, ρ=A͞K, ϕ = angle of rotation of radius vector ρ, ϕ₀ = initial angle.
$1236$LG,Ge$