Stropping dulled my edge?

T

ThatsMyKnife

Joined
Dec 4, 2012
Messages
78
Yes it did.
I used my knife on my 250 grit then 1000grit stones. It was cutting paper fine after the 1000grit but not push cutting well.
So my next step as always was to use Bark river black compound to put a slight convex on the edge. After a good stropping (at the right angle ) I tried it on the paper again and to my surprize it cut worse then after the 1000grit. So at first I thought it was my fault so I stropped it up again but it was no better. So I took it back to the 1000 and repeated the the whole nine yards.

After the 1000 I felt the bevel and it was a pretty even V grid, after the stropping (on black compound ), I felt the bevel again and it had gone convex. Now I know this is susposed to happen because the black compound is quite good at making a convex edge imo ( I love convex edges ). But why would my knife suffer in cutting performance after it has been convexed? The blade is quite thin if that is a factor.

Thanks.
 
ThatsMyKnife said:
Yes it did.
I used my knife on my 250 grit then 1000grit stones. It was cutting paper fine after the 1000grit but not push cutting well.
So my next step as always was to use Bark river black compound to put a slight convex on the edge. After a good stropping (at the right angle ) I tried it on the paper again and to my surprize it cut worse then after the 1000grit. So at first I thought it was my fault so I stropped it up again but it was no better. So I took it back to the 1000 and repeated the the whole nine yards.

After the 1000 I felt the bevel and it was a pretty even V grid, after the stropping (on black compound ), I felt the bevel again and it had gone convex. Now I know this is susposed to happen because the black compound is quite good at making a convex edge imo ( I love convex edges ). But why would my knife suffer in cutting performance after it has been convexed? The blade is quite thin if that is a factor.

Thanks.
Click to expand...

do a lower stropping angle. you could be rounding the apex or making the edge way too obtuse
 
^It's better to go too low an angle and not hit the apex, than to go too high with alot of pressure. Yeah, make sure not to use alot of pressure. I don't know how competent you are with removing a burr, but you might just be thinking that the edge is cutting well when it's just the burr(Probably not super likely, especially at 1000 grit).

I was guilty of going too low yesterday while touching up some edges. I was like WTH, I've done at least a few dozen strops per knife and they aren't hair popping. Increased my angle 10 degrees and voila! I sharpen on a belt sander, and the belts kind of conform to the blade, so I think that the angle that I see is probably a lot smaller than the final angle on the convex edge. Making it a must to do any increased "appearance" angle when stropping on a hardback strop. Hopefully someone understand that :(
 
ThatsMyKnife said:
Yes it did.
I used my knife on my 250 grit then 1000grit stones. It was cutting paper fine after the 1000grit but not push cutting well.
So my next step as always was to use Bark river black compound to put a slight convex on the edge. After a good stropping (at the right angle ) I tried it on the paper again and to my surprize it cut worse then after the 1000grit. So at first I thought it was my fault so I stropped it up again but it was no better. So I took it back to the 1000 and repeated the the whole nine yards.

After the 1000 I felt the bevel and it was a pretty even V grid, after the stropping (on black compound ), I felt the bevel again and it had gone convex. Now I know this is susposed to happen because the black compound is quite good at making a convex edge imo ( I love convex edges ). But why would my knife suffer in cutting performance after it has been convexed? The blade is quite thin if that is a factor.

Thanks.
Click to expand...

The bolded part above is the clue. The fact that the edge was slicing paper, but not push-cutting, suggests the edge probably wasn't fully apexed, or the edge angle is too wide (obtuse). The teeth left on the edge from the stones were doing most/all of the real work, and stropping likely removed most of that, leaving what is probably a wide or relatively rounded/blunt edge behind. Convexing will likely leave the edge angle even wider, which compounds the underlying issue.

Ideally, you should have the edge cutting well off the stones, and stropping should improve on that. If the edge is failing to cut prior to stropping, it's very rare when stropping will actually fix that. Especially when convexing on a strop with fairly aggressive compound (like black), which will always make the edge angle a little more obtuse, and probably a little more dull as well (as you've found). Shaping a convex is best done on stones or very firmly-backed abrasive (like sandpaper), using progressively lighter pressure as you refine the edge. Stropping is meant to refine/perfect an already good edge, but rarely will improve a poorly-performing one.


David
 
Last edited:
The above ^. Do not convex with a strop, you'll round the apex very easily unless your backing is extremely hard - at which point you've crossed over to more of a lapping process. Off the 1000 grit waterstone (I'm assuming here) the edge will still be somewhat toothy, so crosscutting paper but with some noise is not a bad edge at that level. Also the black compound should compliment that edge very well. Lighten up the pressure and make sure your strop is real firm. A good trick is to make four or five dots the length of the blade bevel with a Sharpie once you're done with the stone work. Check those dots every pass on the strop to see where you're hitting and how much pressure you're using. It should take multiple passes to erase those dots, and they should fade evenly.

HH
 
Very good advice so far. I used to do the same thing(rounding the apex) and I'm sure alot of us have. Do you have access to a jewlers loupe and good light? And remeber less pressure while stropping and sometimes not hitting the apex is better than to much pressure and rounding that apex. Less is more when it come to stropping IMO.
 
Everyone here has good advice and I agree. Your probably rounding the apex. I used to do this when I first had a strop. It takes time and practice to get it right. Also like others said your apex might not be fully ground. 1000 grit should push cut paper, I can get my edges to push cut thin magazine paper off 1000, after I strop they'll cut even better.
 
Read the sticky at the top of this forum:

Stropping: angle plus pressure

I found it very helpful when I was getting duller edges after stropping. I still don't get much improvement from stropping, but at least I don't dull the edges and it's a bit more shiney.

Allen
 
Thanks for all the advice guys. For some reason this knife gave me alot more trouble then normal, or maybe my sharpening "mojo" was off that day. Anyway, its hair poppin' phonebook paper slicing sharp now. Thanks.
 
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