IMHO, I think the problem your having with sharpening the Sentinel on the Lansky, is the false edge. Spine clamping systems like the Lansky, do not like false edges. When you tighten the clamp using the Lansky on a false edge, the blade of your knife wants to tip sideways up or down, causing uneven bevels. The only way to compensate is to put the blade deeper into the clamp, which in turn causes steeper bevels, (Let me say that false edges, IMHO, should be sharpened with a system such as Spyderco's Sharpmaker, or freehand, if you have the touch). If you must have a false edge, and want to use a system such as the Lansky, you have to make sure the bevel is equal on both sides. On a Lansky this is critical. Once you tighten the clamp, look at the tip of the blade from the spine down and make sure it is straight, and that the blade IS NOT tipped to the right or the left. Start off with the 30, (or if you prefer 25), degree angle, (using the coarse or medium stone), until you feel a slight burr on the whole edge of the opposite side, then flip it over until you get the same results. Then do the same with 25 degrees, then end with 20. Put a rough edge on or a polished edge, (your choice). Once I get past the 30, (or 25), degree step, I switch to an optional Lansky fine diamond stone, (makes quick work of the sharpening), to finish the 25 and 20 degree steps. If you want a coarse edge, finish with the medium stone. If you want a good utility edge, finish with the fine stone, and if you want the polished edge, finish with the extra fine stone. One more point, when you get this procedure down, make sure to mark your clamp or make a mental picture of where you had the blade clamped. This way you will know how deep your clamp should go when you tighten it down, and you can just touch it up with the 20 degree angle. Also as Joe T. says, you can strop it on an old leather belt, or the cardboard back of a writing tablet.
