Sharpening on cardboard???

[Robson Valley]

I think this is why I'm satisfied with a leather strop glued to a piece of wood.
I realize that it's no flatter than any piece of cardboard tablet backing.
However, it's possibly a little softer so it deforms against imperfections in the sweep of a gouge.
I ignore that as I'm rotating the shaft of the gouge in the pull stroke, anyway.

What I do see, like everybody else, is that the abraded metal particles are the black streak.
As long as I can keep the axis of the gouge at 20 degrees, the results are entirely adequate.

[bob easton]

Originally Posted by woodsman1st

... the ends on both the Flexcut and the Dockyards are not straight across; a few are wavy with the center in towards the handles more than the corners; on the others one side will be longer than the other side....

That's an indication that there's more wear in the center than at the edges. Ideally, you want to see the edge even all the way across, and the corners (of gouges) NOT rounded.

When you get to sharpening (scary sharp works great) give those outside parts more work than the center. Bring them into square all the way across. All it takes is a little practice and attention.

[Robson Valley]

And then there's "scary sharpen dings" when you realize that the best thing to do is square off the end of that lovely gouge and start over. The first one gave me butterflies.
Bob's right: you want the bevel even, all the way around the sweep. His method to lean on the corners more is easier to the mind than what I have done.
Then I read about the gang who like forward swept corners and the other gang that like back swept corners. . . . . . . square is OK.

[richipper]

I just recently started flattening my leather strops on the stationary benchtop 4 inch belt sander. I thought my strops were flat before... now I know they are flat. I even stripped the Flexcut strop and flattend the wood then re applied a decent piece of leather on with spray adhesive then sanded the leather again. Looks and works great. I know the gouges will make it uneven if I let it.
But that is why I have more than one strop.
Richard