  We present three large families of new examples of plumbed 3-manifolds that
bound rational homology 4-balls. These are constructed using two operations,
also defined here, that preserve the lack of a lattice embedding obstruction to
bounding rational homology balls. Apart from in the cases shown in this paper,
it remains open whether these operations are rational homology cobordisms in
general.
  The families of new examples include a multitude of families of rational
surgeries on torus knots, and we explicitly describe which positive torus knots
we now know to have a surgery that bounds a rational homology ball.
  While not the focus of this paper, we implicitly confirm the slice-ribbon
conjecture for new, more complicated, examples of arborescent knots, including
many Montesinos knots.
