A parallelogram mechanism of violet conrod and two blue cranks can slide on two yellow rods.
Red tracer is on one crank, orange cutter is on the other. Their distances to pink bar pivots are equal (the tracer and cutter can be on the violet conrod also)
Move (by hand) the tracer along profile of fixed cyan template, the cutter creates a surface on fixed yellow work corresponding to the profile of the template.
The tracer and the cutter are kept perpendicular to the ground.
The tracer and the cutter diameters must be equal if profiles of the template and the work are requested to be the same.