F to XF Sharpness

[dykesc]

I've noticed something I'd like to get some insights on. I am sharpening flat grind, single beveled edges on fine and extra fine DMT diamond stones. I am using edge first strokes. What I have noticed is that I can get a very sharp edge after finishing with the fine stone (Push cut paper, shave, etc.) After I go to the extra fine stone, the edge seems to degrade (hangs in paper, won't shave). Once I strop the edge following the extra fine the sharpness returns sometimes. I am being very careful with angles so that is not the problem. I don't have burrs after coming off of the extra fine. (I feel for them and also use the hanging straight pin test) Any idea on why the edge seems to degrade following use of the extra fine diamond stone? I have experienced the same thing when using 1500 grit sandpaper on a glass plate backing.

Thanks for replies

 

[theonew]

Perhaps you're angle is too acute for the steel you are sharpening and the carbides are tearing out

 

[Jason B.]

Feeling for a burr with your fingers and using the Pin test is only going to work to a point. Looking for reflections under bright light or stropping the finger nail surface are some better more accurate way of detecting the burr, even when stropping. Another big factor in using diamond stones is pressure, light pressure is one thing but I find that barely even touching the edge to the stone makes all the difference, if you are using more than blade weight your using far too much. I was told by a DMT rep and found it to be true for myself that the lighter the pressure you use the finer the finish will be. Also use soapy water with the finer stones, it really improves on the finish and outcome of the edge.

As for the going from sharp to not so sharp part its probably because you have not equaled the grit, meaning that there are still scratches from the previous grit.

I like my diamond stones but for single bevel knives I still prefer waterstones.

 

[dykesc]

Theonew and Knifenut thanks for excellent advice. I'm working with AUS4 AUS8 steel so maybe that's got something to do with it (carbide structure). Also will lighten up pressure and use soapy water with the XF diamond. I have been using the XF diamond stone dry and cleaning it frequently rather than keeping it wet.

 

[Ben Dover]

You might even try supporting about half the weight of the knife. IME, just the weight of the blade is often too much pressure.