Here's my secret for doing rolling halfstrokes: The rolling motion has to come from the upper arm. Right now, while you're sitting in front of your view screen, allow me the illustrate that. Lift your right arm (if you hone right handed) and raise your fore arm in front of you, parallel with and above the spacebar of your keyboard. Mimic holding a razor. Lift your elbow while lowering the wrist, and alternate that motion, lowering the elbow while raising the wrist. Tell your wife to mind her own business.
The motion you now did is the basic motion that is added to a half- or a full X-stroke to get a rolling stroke. The amount of roll can be very precisely controlled by how much the elbow is raised and lowered. Note that this motion is automatically diminished at the razor, because the elbow sits on the long end of the cantilever that has your pols as a fulcrum.
I hope this makes sense somehow. A lot of people perform the roll by moving with their fingers. That works well for the X-stroke, but not for halfstrokes because the finger on the blade interferes with that technique. Put the roll in your entire fore arm, and not only you will be able to use the same rolling technique for X-strokes and halfstrokes, but you will be in better control as well.
Observing myself, I have to admit that I always have some amount of roll in my strokes. On most razors, it's not so much a real roll, but rather a gradual shift in pressure: first on the heel, over the middle to end on the tip. And reverse while pulling the razor back.
Before staring halfstrokes, I will always seek the right motion for that razor, by performing a few slow X-strokes while I closely monitor how the fluid behaves in front of the edge. Basically, it has to first run up the heel, evolve to running up the middle halfway the stroke and run up the tip near the end of the stroke. It takes me 3 or 4 careful X-strokes to find the right motion and lock it into muscle memory. Next I start the halfstrokes with the same curve. I sometimes stop to check the edge with a TPT. At that point I re-calibrate the stroke in the same way as described above.
Another important aspect of my personal honing style, is that while correcting the bevel, I don't worry much about a constant repetition of identical strokes. If a TPT reveals that part of the blade stayed behind, I will put a finger above that part and even might make partial strokes that only work the affected portion of the edge. It is key to regularly check the shape of the bevel, how easily the slurry runs up the bevel, if the edge sits more of less in the middle. A bevel always tells a story with the the shape it takes. It might tell you there's some warp in the razor, if might reveal uneven spots in the grind (often found in razors that were heavily sanded during a restoration process). It might tell you that the spine is thinner near one end. It might tell you that a frown is developing, or an exaggerated smile. It might reveal a slight loss of bevel symmetry. At first, it can be difficult to decipher the language of the bevel, but with experience if becomes second nature and in most cases possible to tell what's going on with a quick inspection.
As always the case with abrasive action, we have to work at the high spots and omit working at the low spots. If that calls for working only the tip or heel half of a blade, or favoring one side of the blade more, that we must not hesitate to do so. By the time we call the bevel good, it must be good. It defines how easily the edge can be turned and kept into perfect shaving condition for years to come. We must stay at the helm, while sharpening a razor and continuously steer the process till we arrive exactly where we want to be.
Kind regards,
Bart.