Rolf,
There's enough infor already to get you started.
Maintaining the same sharpening angle is important in maintaining the same cutting characteristics after each sharpening.
An easy way to do this is to make a length gauge, to maintain the same angle without the hassle of using a protractor each time.
To make a length guage, get a piece of tubing (copper, steel, plastic) that fits over the graver.
As Jerry points out, put the graver in the sharpener, and adjust it with the protractor until you have 55 degrees for the face, and lock it in place.
Slip the tubing over the graver, then cut it off exactly at the tip of the graver. Cut, file, smooth, until the tubing is the exact length.
Do the same for the 20 degree heel length.
When you need to re-sharpen the graver (which you will), put the graver into the sharpener gizmo, slip the tubing over the graver, and align the tip of the graver to the end of the tubing,,, and you'll be re-sharpening at the same angle.
A square 90 degree graver is all you'll need to start.
As per Jerry again, the heel should be short; 0.25mm to 0.50mm. A longer heel will help to maintain a straight line, but will mar the line when cutting a arc or circle. A short heel makes it easier to cut a arc or circle, but is harder to maintain a straight line.
Keep in mind that the heel angle will be the angle you hold the tool for cutting. If 20 degrees isn't comfortable for you, hold the tool in a comfortable way, measure the angle, and cut your heels to that angle. Think of the heel as the keel of a boat as it cuts through the water.
Be sure your heels are ground equal length. Check them with a magnifying glass if necessary. If they are of unequal length, the graver will have a tendency to cut to the right or left of straight.
And practice on mild steel as it cuts easier than brass.
If your cutting an arc, push, hammer, smoothly while doing it. Don't try to change the direction of the cut without the tool moving, or you will break the tip.
Good luck, John
