\new PianoStaff 8 f' e' f' e' \change Staff = "down" \stemUp b g e Nonetheless the duplication causes the beams to be close to overlapping (fig E).
![dorico cross staff beaming dorico cross staff beaming](https://musescore.org/sites/musescore.org/files/2020-10/L_A_cross-staff_gracenotes.png)
The key result here is that where the two voices contain the same notes, because they are now in the same Staff and assigned to the same Voice, lilypond lets the noteheads overlap such that we don't see the duplication. And you will need to make sure stems continue to point to the middle of the two staves using stemUp and stemDown as appropriate. You also need to assign both to the same voice number (here I assign both to voiceOne). Here we will have the final three notes of the treble voice change to the lower staff, while the first note of the lower voice changes to the upper staff. Next, have the voices change staff where appropriate such that the note heads appear in the correct staff (i.e. Now orient the stems so the beams are in the middle of the staves. Similarly, I will add the final three notes of the bass to the treble (fig C). So, in this case, I will add the first E from the source's treble to the bass so it is present in both staves. The next step is to fill in these gaps with duplicate notes from the other staff. For instance, the upper staff stops with 3/8ths of the bar still to go, while the first 1/8th of the loewr stave is missing too. Next, note how the upper and lower staves of the source are "missing notes". The first step is to write both voices out separately (fig B). Note we will ignore the uppermost treble voice and lowest bass voice as they are not relevant to the problem at hand. cross staff stems with the beam in the middle), as shown in the source (fig A). Edit: I have since found a better method which is faster and less fiddly.