Hi James, thank you for your reply.
I've tried using your proposed method, but it still doesn't get me where I want to be.
When I change the gizmo mode using the pick command, the gismo is oriented to the middle of my polyline, but the X/Y axis are still orthogonal to the default Max grid.
I was hoping to get the Y axis on (or parallel) to the drawn polyline and the x axis with a 90 degree angle to the newly selected Y axis (polyline).
Option 2; when I'm trying to use a custom grid, the grid alignment is not possible along the grid edges, yet only the grid middle(diagonal intersection).
What I want to achieve would be to rotate the gismo and align X or Y axis along any polyline I've created.
Similar action could be achieved just by editing a working pivot(I can drag it, snap it, rotate it), but it is never a 100% accurate solution (rotation angles differ up to 0.00032 degrees for example).
I've attached 2 screenshots showing what the problem/wishes are.
Best regards