There is a lot of good advice here but it can be confusing when you get too much. I suggest you only learn how to sharpen two gravers, A 90 degree or square graver and a flat graver. Start with the flat graver because it is the simplest. If you learn from professionals you will save yourself a lot of problems later on.
This is advice for some of the others. Depth control is mostly caused by the heel being too long.
A graver pivots on its heel not just left to right but also vertically. The longer the heel is the more it magnifies the errors your hand makes. Take a pencil and put your finger in the middle of it for a pivot point. When you move one end the other end pivots on the middle where your finger is. If you move the pivot point near the end, then when you move the long end the short end will not move much. This is how a graver works. So the shorter the heel is the less it magnifies your mistakes.
There is one limiting factor to a short heel. If you go deep enough to where the graver is in the metal past the pivot point of the heel you cannot come out of the cut.
When I teach engraving I usually spend the first day just on graver geometry. Advanced graver geometry is a lot more complicated. Most of you will never get that far into engraving.
PS
It’s not enough to know how to sharpen a graver, It is important to know why it has to be that way.
