Sliding element is basically aluminum square tube with UHMWPE pads. The square tube pieces are made using SVG templates. UHMWPE pads are cut out from channel stock, drilled and fitted inside, held by plastic screws. Some hacksaw (or Dremel) work is required to thin the areas where UHMWPE pads touch the angle rail. The friction is adjusted by small screws.
Detailed howto: http://contraptor.org/make-sliding-elements