Thanks alot bill and other fellows for sharing this tip
Bill, do you have some picture of the mandau before using your tip

i would like to see comparation before and after rust removal.
Regarding the pienapple rust removal, we usually used the Pineapples/ Pineapples skin to remove hard rust. Just rubbed the rusted area with Pineapples skin couple of times until the rust fade away.
just my 2 cent