Consider a cubic surface cut out by equations $x^2y - z^2w$ inside $\mathbb{P}^3$. This gives a cubic surface with a line of nodes, it is toric and has normalisation $\mathbb{F}\_1$, a Hirzebruch surface.


My confusion is two fold, I am having difficulty spotting which two torus invariant lines of $\mathbb{F}\_1$ are being glued together.


In addition I would like to understand how this degeneration works with respect to the 27 lines on a cubic surface and see where degenereate to.


\*\* Edit:\*\* Sasha's answer has made me delete some of my post as it has clarified why it is wrong, and now it is unhelpful and long.



Lines on a toric cubic surface with a line of nodes
The cubic scroll in $\mathbb{P}^4$ is isomorphic to $\mathbb{F}\_1$ and its torus-invariant divisor has three line components and one conic component. The linear projection $\mathbb{P}^4 \dashrightarrow \mathbb{P}^3$ from a point lying in the linear span of the conic, but not on the conic itself, gives the normalization map 
$$
\mathbb{F}\_1 \to X = \{x^2y - z^2w = 0\} \subset \mathbb{P}^3.
$$
Thus, instead of gluing two lines, it collapses the conic onto a line via a 2:1 map.


