I did most of black Ark lapping on a DMT 220/325 Duosharp. The rest was w/d on the back of a DMT Diasharp - 220-2k.
It took me several long sessions to get it done. My stone is 10x3x1 so that's partly why it took a while longer than one would think. I bought a ton of cheap w/d on eBay to do the heavy work. I used 3M for the later stages, but I can't remember if the 1k & 2k is 3M. Whatever it was - it wasn't the cheap stuff.
Your issue with the ends polishing and the middle bellying is probably due to abrasive building up in the center of the stone when lapping. Light pressure figure 8 laps under running water help prevent that. Another thing I noticed, when lapping- toward the end of the journey, the Ark's top surface seemed to go from almost-done to a less-flat state right before it all came together. I don't know if that makes sense, but it's almost as if the last final waves in the top all become visible at once, and rhen they all iron out at the same time.
It took me several long sessions to get it done. My stone is 10x3x1 so that's partly why it took a while longer than one would think. I bought a ton of cheap w/d on eBay to do the heavy work. I used 3M for the later stages, but I can't remember if the 1k & 2k is 3M. Whatever it was - it wasn't the cheap stuff.
Your issue with the ends polishing and the middle bellying is probably due to abrasive building up in the center of the stone when lapping. Light pressure figure 8 laps under running water help prevent that. Another thing I noticed, when lapping- toward the end of the journey, the Ark's top surface seemed to go from almost-done to a less-flat state right before it all came together. I don't know if that makes sense, but it's almost as if the last final waves in the top all become visible at once, and rhen they all iron out at the same time.