(02-28-2023, 07:28 PM)imapseudonym Wrote: I usually use scrapers with that profile as sheer scrapers (handles dropped way down, corner of the tool on the tool rest so the sharpened edge presents about a 45* angle to the surface. Used that way, I don't normally but a negative rake grind on them.

If you do want it to be a negative rake to be used flat on the rest, the combined angles of the two bevels have to be less than 90* or it won't cut. An 80* main bevel with a 15* negative rake would be more than 90.  I think my negative rake scrapers have a combined angle somewhere between 70 and 80*, I haven't noticed much of a difference if it is the same angle on each bevel (say 40*) or if one is steeper than the other, except that if they are the same angle it is easier to flip the tool over to get the opposing profile.