Outside of Transforming objects, is there a way to constrain movement on an axis? Similar to what you do in Photoshop when you want a drag either horizontally or vertically by holding the shift key.
Just press the axis letter, or shift+letter to move on all but that axis.
No, what I mean is, let’s say I want to use the knife tool and I want the next cut of the knife to be perfectly perpendicular to the 1st cut I just made. How would I make it do that? Or even the case that I want the 1st incision to travel along a particular axis. Is there a way to make it only go along that axis and not other direction?
Using the knife tool if you press c it will constrain to the knife tool either in increments of 45 degrees it looks like.
As a59303 said, you can use ‘c’ to contrain the knife, (z to cut through or it will only cut the facing polys).
If you want 2 cuts directly perpendicular, I tend to cut once, with the edge still selected, Ctrl+B to bevel to create my second slice.