I've tailored my method of sharpening on the grinder, to match the flow of how I make knives. Most of what I build are flat grinds, with convex edges. When I come off my final grit belt during finish grinding, my goal is for a blade to be "ragged sharp". That is then cleaned up/accentuated during hand finishing. (usually, the "convex" edge is installed at my 220 grit belt during finish grinding, and then just cleaned up with successive grits until I'm done)
With the flat platen attachment in place, I utilize the slack belt area between the idler/tracking wheel, and the top contact wheel of the platen, (this can also be done with a large contact wheel in place....but I find it's easier to "reach" that slack belt area with the flat platen on the machine) with the blade's edge going into the direction of belt travel. I can't give any specific "angles" because it's not an angle....it's a convex, so I sharpen mostly by feel. How large or small that edge convex is...... is determined by down pressure, and the flex of the belt you're sharpening on. Obviously the flex is going to differ between and "Y", "X", and "J" weight belt....so, if you use various grits with this method, try to use the same backing weight for this type of sharpening. With some practice, you can learn to feel where the belt is cutting.
Unless the blade's edge is very banged up/dinged up, there's very little pressure applied, more of less it's just the weight of the knife. I start just like I grind blade...... in the middle of the blade back to the plunge/rear of the edge, then a pass all the way to the tip of the blade.....and repeat on the opposite side. With most blades completed/pre used knives, it's only 1-2 passes per side.
In the case of severe dings or dents in an edge, I will usually just grind a flat on the edge, until I get rid of the dents/dings, and then sharpen as I described.
Some caveats/variances.....
*This is best accomplished on a variable speed grinder, with the belt traveling SLOWLY. For example, it's usually 15% or less on the VFD dial of my grinders.
*The necessary steps are widely different for Carbon/alloy steels versus Stainless
**For carbon/alloy, were the edge(s) are not damaged, I use a worn out 400 grit belt, and that's typically it.
**For Stainless, it's necessary to go through a progression of grits.... again, if the edge(s) are not damaged, I start with a worn out 400 grit, but then, I step through successive grits to either 1200 or 2000, depending on the type of stainless I'm sharpening.
**For "collector" type knives, I follow the sharpening up with a pass on edge edge (edge down) on a loose buff with Pink No-Scratch compound. (most collectors like to "show off" how their knives will shave hair from their arms)
**For "user" knives, I often do not buff, but leave a "bitey" edge that the worn out 400 belt, or in some cases 600 belt produces. This edge my not necessarily shave hair all day long, but most of my "user" clients prefer it, saying that it's far more aggressive, and the edge seems to hold up longer under harsh cutting tasks. However, there are some of my less experienced clients who want it "shaving sharp", and for those I don't even try to convince them otherwise.....and give their knife/knives the buffed edge treatment.
BEWARE! THERE IS A RISK OF SOME CHEAP BELTS, WHO'S JOINTS ARE LESS THEN PERFECT, CATCHING/JAMMING INTO THE CUTTING EDGE....MEAN IT COULD JERK THE KNIFE OUT OF YOUR HANDS, OR JAM THE BLADE OR TIP INTO THE BELT.....SO UNTIL YOU ARE CONFIDENT THAT'S NOT GOING TO HAPPEN, IT'S BEST TO HAVE A "DEATH GRIP" ON THE KNIVES/BLADE YOU'RE SHARPENING....AND EVEN THEN, DON'T TRUST IT.....JUST MAINTAIN A GOOD GRIP. Remember "There's traps everywhere for a man!"