vertex slide and snap not working together How can I modeling these case more efficiently?

This post is an extended question from the link above.
I have covered the efficient way of doing indent in the previous question.



Like the GIF above, I finished the indent and wanted to flatten the bottom with the finish. I wanted the vertices to move numerically precisely. If the underside was aligned with the world axis, we could solve the problem by using the axis locking function and the snap function together, but we wanted to use the vertex slide function and the snap function together because the bottom surface has a different slope from the world axis.

But why Vertex slide did not work with snap in blender? So I eventually zoomed in as far as possible and placed the vertex as close as possible to the snap point on the underside.

In fact, I'm working on visuals rather than on product creation and i don't need numerical perfection. So I'm not uncomfortable using boolean cutting to flatten it. But I wanted to know more about the modeling technique, so I wrote this question.

 How do I snap a vertex(vertex slide derection) to a plane with a different slope from the world axis?
GG doesn't snap, perhaps because if you use it on multiple vertices, they all move in different directions.. (I think it still could be implemented, but that's another story)

G along a defined axis does snap, so you just have to create a defined axis from the edge you're sliding down, by creating a Custom Orientation from it. In 2.79, that's CtrlAltSpace. In 2.8 there's no default keymap.. it's the '+' in the Transform Orientation dropdown in the header. Ensure 'Use after Creation' is checked. So it's:


Create a Custom Orientation from 2 vertices, or the edge you're sliding down
GYY move the selection parallel to that line, snapping the source (usually snap: 'Active', with a vertex made active) to a target vertex.


But this will only snap to a plane thrown perpendicular to the axis, around the source vertex. Sometimes that's not what you want. So more generally, instead, set a Pivot-Pointon the plane you want the entire selection to flatten to, whose normal is the edge you've made into a Custom Orientation, and SYY0 the lot.

You can make a Custom Orientation from 3 (or more) vertices, defining a plane. Blender generally  calls the direction down an edge or a curve 'Y', and the direction normal to a plane 'Z'. So to flatten to a defined plane:


Create a Custom Orientation from 3 vertices, or a face
Set a Pivot-Point you want your selection to flatten to, parallel to the defined plane
Hit SZZ0