HiThe router should be able to move freely up and down to follow the shape of the back – on my binding jig it moves smoothly on a linear bearing – there are no springs…https://www.stewmac.com/Luthier_Tools/Types_of_Tools/Jigs_and_Fixtures_for_Guitar_Building_and_Repair/TrueChannel_Binding_Router_Jig.htmlMore importantly your cutter is UNGUARDED…   Read more»