I’ve watched a few videos, read a blender.org article, and also see a tutorial in a book all about the knife tool, but I can’t get it to behave the way they all do. I cannot draw freely, I only get straight lines. What am I doing wrong?
Also, what is the difference between the K and Shift-K for Knife and Select? The latter doesn’t do anything for me when I press Enter after using the knife.
Yes, the knife is not a free cutting tool, you can only cut in lines, so to cut in a curved way you need to make several small cuts , by example like this :
SHIFT+K is supposed to allow the knife to cut only on the faces that are selected, something very usefull.
But that’s the theory, in practice SHIFT+K is extremely buggy to the point of being completely useless because it will miss nearly all the cuts you want to do (though the regular knife has sometime problems too).
It’s a long time standing bug that has been reported but must probably be very hard to fix as it’s still there after all that time. So just avoid it unfortunately and let’s hope it will be fixed one day.
This must be functionality that was removed. The knife tool certainly used to allow freeform drawing, as noted in several tutorials. Even the wiki shows an example of this:
And I’ve seen videos where people are using it to draw freely in realtime.
The screenshot you show me is from Blender 2.4x (the last version of Blender from the 2.4x serie was Blender 2.49b), the knife was working very differently (much better in most ways as it never missed a cut and you could constraint it to an axis, but worse in ways because it wasn’t possible to cut inside of a face exactly the way you wanted by example the curved cut inside of a face from my previous screenshot was impossible with the 2.4x knife).
Hopefully one day we’ll get an improved knife with all the good functionalities and without the problems in Blender 2.6x.