Common sharpness for double bevel edges?

[grepper]

When I sharpen a double bevel blade, 95% pop out in the 140 – 155 gf (PT50B) range without really jumping through any hoops. Most of the time, right about 150 gf.  Just a basic sharpening.  When I see 160 gf or greater, I always suspect that there is still burr.  When that happens, a little more deburring will almost get the blade back to expected sharpness.
 
I have no idea what’s up with that 150 reading.  For whatever reason, my method of sharpening/deburring just produces edges about that sharp very predictably.  If it’s much sharper than that I am surprised, and if it’s much duller I suspect burr.
 
It seems that it is common not only for me, but also for others, to generally end up right around 100 gf for single bevel edges.  I wonder if there is some similar, common sharpness that folks see for double bevel edges.
 
So, I’m curious – what sharpness do you guys usually end up with when sharpening double bevel edges?

I'm not asking how sharp you can get a blade.  I'm just curious as to if there is some common sharpness for double bevel edges that you guys see after a basic sharpening and deburring.

[Mark Reich]

Mr Grepper, I know you have stated several times that you end up with the same numbers on each freshly sharpened blade.

Don't you always, or almost always, finish on a leather belt? I haven't heard otherwise, so I have to ask.

IMHO, if you finish the same way, you're going to end up with approximately the same edge. I'm not sure what else to expect. Your last action is going to have the most effect on the finished edge, right?

Again MHO, if you want to expand your horizons, you're going to have to start cutting stuff. I guarantee you will find tremendous differences in edges that always start at 150gf.

[grepper]

Yup.  I always deburr with the rough side of a Surgi Sharp leather belt.  I do that because I’m trying to not degrade the toothy edge, so I stay away from abrasives when deburring.
 
I should qualify the 150 gf reading to some extent.  That is for a quick, basic sharpening.  By that I mean create a burr on one side, flip the knife and create a burr on the other side.  Then deburr with a few strokes @ ~45° and some at close to 90°, etc...  Doing that I see around 150 very often.  Rather surprising methinks.  Of course, it does vary from with different blades with different steels.  Sometimes it’s very quick, but some types of steel create those annoying super malleable burrs that just bend and bend.  I can understand the temptation to abrade those away, but I just mutter under my breath and soldier forth.
 
After you describing burr fall off like rain I tried a coarse DMT diamond plate.  I was probably doing it wrong because is just messed up the edge.  Maybe it was too coarse or I was pressing too hard.
 
If I really take my time I can get edges down to 115 or so.  You know, stuff like more alternating strokes on each side, progressively lighter and light strokes to slowly reduce burr, being very careful about maintaining a consistent angle and more attention to deburring.  I don’t bother with that often because 150 is about what I’m looking for.  For some dubious reason I’m under the impression that much sharper than 150 probably won’t hold up as well.  That’s just an impression I’ve formed after using sharper blades.  I have not actually tested that so I could just be blowing smoke, but I blindly blunder forth under that impression.  On the other end of the spectrum, I’m not satisfied above a160 gf reading.
 
I have no doubt that you are totally correct that I would see performance differences in edges and that I should cut more stuff and do retention testing.  Very sound advice.   Depending on how I feel at the moment I may sharpen from 80 – 150 grit and no doubt those edges would perform significantly differently depending on what is being cut.  I just sharpened a cheap paring knife and the crappy steel just crumbled with a Cubitron II 120 grit belt.  Then I tried Cubitron 150 grit with the same results.  It finally took and edge with a slightly used 180 grit Deer ceramic belt.  I didn’t bother to change the grinding angle, just went to a finer abrasive until it worked.  But hey-  I got the little $0.99 Salvation Army thrift store find knife sharp.  I was happy.
 
All that said, I’m pretty happy with the toothy 150 edges that my quick sharpening method produces.  They perform very well cutting a variety of materials, and seem to hold up well even with just average steel blades.  I’d love to have some super steel blades to play with.  I’d like to compare sharpening methods, varying levels of tooth and deburring techniques but I keep being put off by the cost of those blades.  Super hard fine steel is always pricey. 

What!? Expand my horizons?  My God man! What are you suggesting? Learn something new?    You are indeed a wild man Mr. Mark.

[grepper]

It seems there is some agreement that single bevel (sb) edges are easier to get sharper than double bevel (db) blades, and I noticed that ~100 gf reading for sb edges mentioned a number of times.  From what I've seen, most of the time folks are not getting db edges that sharp, so I was curious if there is some sort of common sharpness level folks are seeing in db edges. 

I kind of get the idea that, for whatever reason, ~100 is pretty easy to get with sb edges, but double bevel edges are apt to vary wildly in sharpness and be less sharp.  That's why I asked the question in the OP.  I was curious if there was some commonly seen decrease in sharpness between db and sb edges, or if db edges are just all over the place as far as sharpness goes.

Maybe when it comes to db edges with all of the variables involved, the question really does not make much sense.  I really have no idea, so I asked the question.

[Jan]

From a physical point of view the 150 gf reading corresponds to certain edge apex width. Based on Mike’s data it can be ca 0.3 microns. When we see the 150 gf readings often, than standard sharpening and deburring process produces very similar edge apex width.

Smaller readings for single bevelled blades mean that it is easier to get smaller apex width for them. An additional factor may be, that the flat side of the blade penetrates through the test media with smaller friction than the bevelled side.