Torsion arm PolyUrethane

Torsion suspension arm manufacturing guide. These instructions/notes are only used when manufacturing the torsion arms with poured polyurethane bushings and are NOT normally part of the assembly process.

PU = Polyurethane Shore 60A (Vytaflex) Sealant = Lard (there's probably something better, but this works and is non toxic, cleans up with soap.)

• preparing jigs (part1)

  • 3d printed plastic components are used to correctly space the torsion box, and center it on the axle shaft.

  • sealing all edges is critical, otherwise PU will find a weak point and leak out

  • coat lightly with sealant

• preparing metal

  • The torsion box edges are to be sealed quickly (ahead of time) using simple white glue along the OUTSIDE of the welded edge/tabs. this is a precaution to prevent PU from seeping out.

  • The axle "large circle" is sealed with white glue on the INSIDE edge in order to prevent PU seeping.

  • the inside of the torsion box and the axle shaft area that sits inside the box are degreased and cleaned with brake cleaner

  • Be careful not to touch the cleaned axle area afterward

• Jig assembly and sealing (part 2)

  • plastic jig parts seal around the edges using lard (there may be other options, but this is what has worked so far)

    • the entire plastic part can be lightly covered in lard also to prevent any excess or spilled PU from sticking

    • on the lower section:

      • seal between the two halves with jsut enough so that it barely squeezes out the top when tightened together.

      • seal around the inside diamond that presses agains the shaft

      • seal around the perimeter where the torsion box touches the plastic

    • loosely assemble the lower plastic around the uprigth axle

      • axle is standing on the circle end

      • be careful not to touch the clean surfaces

      • some sealant will squish out already

        • tidy this up if needed. Ensure you see a continuous seal around the diamond axle shaft opening.

    • place the torsion box on the plastic.

      • push down slightly to ensure the space is correct between the large axle circle and the torsion box. i.e. make a sandwich with the plastic jig.

      • Make sure the edge of the torsion box is sealed

      • ensure the long flat edge seems sealed ,you can add extra sealant along the back edge as well.

    • install the M5 screws and gently tighten

    • tighten the two halves of the lower plastic jig

    • fully tighten the M5 screws.

    • Check everywhere for possible PU leak points. Add extra sealant as necessary.

• Pouring Polyurethane

  • (know how much you will need)

  • Mix exactly

  • Use the 3d printed funnels

  • don't overfill or under-fill

  • protect the table top from spillage

  • protect from possible leaks (inside the shaft too)

  • Coat anything you want to be able to remove PU from with sealant

  • Use plastic gloves

  • have disposable paper/plastic to put sticky things down on

  • Use tongue depressor or similar to manipulate the PU