Hope I'm not too late on this thread. I do have the perfect excuse for not getting to it sooner. I was at a Bark River Grind-in
And the question of sharpening CPM3V came up. And I had a full range of compounds. And Jim Stewart with a CPM 3v knife in hand
We started with a 'factory sharp' edge.
What we found was the following. At around 9 microns (CBN) there was a slight improvement. At 4.5 microns there was a VAST improvement. 2 Microns and people were 'dancing around happy' at the results. Then we kept going - all the way up - 1 micron CBN, 0.25 micron Polycrystalline diamond, 0.1 micron CBN and finally 0.050 poly and 0.025 poly. Converting this to grits 9 microns is ~1500 grit, 4.5 microns ~ 4k, 2 microns 8k, 1 micron 16k, 0.25 microns 64k, 0.1 microns is 160k, 0.050 is 320k and 0.025 microns is 640k.
By the time we hit 0.25 microns, the edges were treetopping arm hair. Beyond that it just became more effortless. Absolutely giddy at 0.1 microns. We quickly ran out of ways to describe the increasing but consistently greater levels of sharpness.
There were a lot of converts in the room. In fact that's all there was of those that tried it on all sorts of Bark River knives, but most especially the CPM 3v, which held an exceptional edge.
For strops we used both the Kangaroo strops and the Nanocloth strops as the substrate or base to put the compounds on. After demonstrating a few simple 'tricks' for doing convex edges on flat surfaces - the strops are mounted using either aluminum for smaller sizes or glass for bench sized strops - people were able to get impressive edge improvements with EASE. After initially loading the strops, no reloading of the strops was done during the grindin (not necessary) after multiple users and knives were done.
So for example, using 9 or 4.5 micron CBN edge improvement was achieved in 15 or so strokes per side. Easy. And further improvements with a similar level of effort.
How sharp do you want to get your knife? Well that's up to you, but clearly increasing levels of refinement, most specifically on CPM3v can be achieved using CBN and Poly diamond preparations that are difficult or impossible to achieve using the standard BR compounds alone. This is certainly not saying that the standard BR compounds are not good as I had the chance to use them in the process of making a couple of knives for myself
What I found most interesting is the good response at the coarser CBN grits. I didn't have any 15 micron CBN with me but I suspect I would even get some improvement at this level, not because of the grit size but rather because of the interaction with the vanadium carbides compared to compounds that don't contain abrasives as hard as the vanadium carbides. Clearly the compounds are refining the carbides themselves rather than just relying on carbide fallout. For this reason I would recommend using the 9 or 15 micron CBN as a starting point for doing edge touchups on edges that after use have dulled a bit compared to a factory edge.