> For the complete documentation index, see [llms.txt](https://nxp.gitbook.io/elmandadero/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://nxp.gitbook.io/elmandadero/guides/manufacturing-guides/torsion-arm-polyurethane.md).

# 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