Mazo, this is where you start. Most engravers have their own variations on angles, but this will give you a start. All flats must be as flat and true as you can get them. They also need to be polished to at least 600 grit. Many go to 1200 grit and beyond. You need a magnifing glass to see that the point is sharp. You would find things much easier with a Crocker jig, About $35.00, but it can be done without.
The very top angle is just to reduce the surface of the main 45° face, to ease sharpening. Rule of thumb on the 15° face, is no more than the depth you are cutting. Too little, and the graver can dig in, or skip out. Too much, and the curve cuts will be ragged. .020 might be a good start, and that would be length, and heigth. You have to grind these angles first, except for that tiny 15° angle. That you can get by stoneing. Grind, then stone true, working your way down different grits as you would sharpen a knife. Finally finish with 600 grit sandpaper or finer, on a dead flat surface.The graver face should be like a small mirror, or very close. Acually, all faces should be that polished. One trick in this, is to lay a brass, or steel rod lengthwise on the edge of an Arkansas stone, set the graver on this rod, adjust the angle the graver sets on the stone, and sharpen sideways, holding that angle as true as you can. Do the tiny 15°last, and just use sand paper for it, on a flat surface, or even laying on the stone if it is fairly true. Don't overdo that one. Then try it out. Start with very light taps, and many of them to move the graver forward. If it digs in and kinda stops. you stop, and make your working angle more shallow. If it jumps out, increase your angle of attack. Whenever possible, when cutting brass, anneal it first. Sometimes cast brass will try to crumble rather than be cut clean. Low carbon steel seems to cut as easily as brass, and sometimes easier. In my experience. Dipping the graver point in very thin oil sometimes helps, but can get messy if you use too much. I usually don't bother. Laurel Mt. Forge has a Chinese white that I found helpful for layout. Once I figured out how thick to use it, and thinned it a tad. You can draw on it with a pencil, and erase with a light touch, if needed, and I need to a lot. It comes right off will a damp rag.