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Thread: Stropping: angle plus pressure

  1. #1
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    Stropping: angle plus pressure


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    A lot of people have noticed that stropping can make an edge duller as well as sharper. Some say you need a lot of pressure, some say you need no more than the weight of the knife. Actually, you need to get the right combination of angle and pressure.
    I tried to capture this relationship visually:
    The black string represents the surface of the leather strop. The wood represents the edge. It is cut to a 30-degree inclusive angle, a popular edge angle for knives with good steel. Ideally, you want the string parallel with the edge bevel.

    First: Proper angle and very little pressure on the strop. With very little pressure, the leather is not depressed significantly and dragging the edge over the strop at the sharpened angle sharpens the entire edge bevel without rounding the edge. People who say you need little pressure are using the correct sharpening angle. Notice the string is parallel with the edge bevel.


    Second: This shows the angle of the knife held too high on the strop, rounding the edge. This is wrong no matter what the pressure.


    Third: This shows the edge held at too shallow an angle, with little pressure applied. This combination of angle and pressure rounds the shoulders of the edge bevel without affecting the edge.


    Fourth: This shows the angle held too shallow, but with a lot of pressure. The pressure compensates for the incorrect angle and the edge is sharpened. Notice the string is parallel with the edge bevel. This combination will sharpen well. People who use a lot of pressure, are using a shallow stropping angle.



    Finally: This shows the correct sharpening angle, but with a lot of pressure. The extra pressure causes the stopping leather’s surface to drag around the edge, dulling it.

  2. #2
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    Thanks for the pics. I was kinda thinking it was like that but I can never strop well.

  3. #3
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    Try holding a too-shallow angle and then using extra pressure, with a slow drag so you can watch the blade angle and keep it from rising. There is an art to it, but that approach is the easiest for me.

  4. #4
    I've learned the best pressure is where the blade feels "sticky" on the strop.

  5. #5
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    I polish the bevels on most of my knives. The bevel feels very slick on the leather when the angle is just right. If the angle is too steep, the edge drags (obviously) and it feels rougher. Same deal if the angle is too shallow, causing the shoulder to drag.

    The more I do it, the more I'm inclined to use as light amount of pressure as is possible (just enough to maintain consistent contact with the strop, without 'skipping' across the leather). I figure if I'm needing to lean into it very hard at all, it probably indicates I didn't quite finish the job with my hones.

    I'll sometimes make a couple of very, very light passes with the angle elevated just a little. Seems to give it just a little more 'bite', with some steels. I suspect it's mostly just scrubbing off some tiny remaining burrs.

    To Twindog:
    Your string & wedge 'visual aid' is excellent. Very simple & a great way to illustrate the concept. Nicely done!
    Last edited by Obsessed with Edges; 08-22-2011 at 10:40 AM.

  6. #6
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    Well stated, I like to use a shallow angle with a bit of pressure when stropping. I use more pressure because my hand sharpened edge has a small amount of convex to begin with and when stropped it tends to match up better.

    Its definitely something that takes time to learn, like with other sharpening tools though you learn the sound and feel then its hard too get wrong.

  7. #7
    I just started stropping lately with an old belt, so it takes me quite a few strokes to get the job done, and I've wound up dulling a few knives doing it. So take my advice with a grain of salt, but this is how I manage it.

    A user here helped me out: He said to slowly move the blade down the belt in a edge-leading stroke, increasing the angle until you feel it "bite" a little. Then you can move the angle back down slightly and start stropping.

    Past that I use a 30x loupe to check my progress every 20 or so strokes. I just watch for little shiny spots on the blade and that the edge is "black". If I see the spots getting smaller, I know the angle I'm working is right. If I see the edge going from black to white, I know I'm working at too much of an angle and dulling the edge.


    What do you guys think about using the marker trick for this? I haven't bothered yet because what I'm doing is working for me.

  8. #8
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    Outstanding post!!! Very informative. Obviously everybody could be right when they disagree on how to strop...because of this little demonstration of geometry. Outstanding post!!!

  9. #9
    Your post explains some of the concerns I have had about sharpening using pieces of box cardboard. A correct angle so as not to actually dull the blade is very important.

    Great post!

  10. #10
    Twin, Good visual aid to demo. stropping . DM

  11. #11
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    Thanks! I just realised the same thing myself-strop is soft mouse pad plus AutoSol. Had been rounding and polishing countless edges before.

  12. #12
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    great that you included the photos, those pics say more than a thousand words.

    I don't strop very light when using Cr2O3, it's easier for me, probably because of me not keeping the angle within a tiny range, which is needed for very light stropping.

  13. #13
    Bump for the great illustrations.

  14. #14
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    thanks any cal. good call
    nice write up by the OP too

  15. #15
    Quote Originally Posted by samhain73 View Post
    I've learned the best pressure is where the blade feels "sticky" on the strop.
    I've felt that stickiness on the strop that you're talking about, but thought I had a different nap on the leather going in one direction.

    I think my left (weak) hand isn't able to hold the exact angle repetitiously like my right hand and that's why it doesn't get the right feel to it many times.

    I'll be looking at this pictorial next time I strop, tonight or Monday. Thanks!

  16. #16
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    Well that's why you need a convex edge! Much more forgiving on a strop.

  17. #17
    Quote Originally Posted by HandofCod View Post
    Well that's why you need a convex edge! Much more forgiving on a strop.
    Maybe so. I've read here that sharpening and stropping eventually puts a convex edge on your knife.

    Not the case if you could hold the edge of a V grind the way that Twindog illustrates. I can always get the edge perfect drawing the blade away or to my right side, but pulling it toward me or to the left is kind of a guess.

  18. #18
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    That was an excellent tutorial! Thanks.

  19. #19
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    Great visualization. I'm like totally impressed, dude!

  20. #20
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    stropping angle pressure

    The best technique I've found is one I lifted from Cape Forge knives back in 96'. Mike explained that a good honing leather is only good for one thing - Making a good edge great,

    It won't make a bad edge good, and it's very easy to dub and dull a good edge with any leather.

    The technique is simple. Lay the blade flat on the leather and push forward while raising the spine in tiny increments. At some point the edge will bite into the leather - that's the angle that you have no choice but to work with because it happens to be the actual angle of the edge.

    Once the edge bites pull back with light pressure and at the end of the stroke just stop - stop and pull the blade up and off the leather.

    If you pull the blade off of the leather at the end of the stroke in an arc, which is a very normal thing to do, you will have undone all of your work.

    Once you experience the level of perfection that leather honing can provide and have a leather honing epiphany you will probably seek better leathers to work with.

    You don't need compound on a good honing leather. The technique works with other things too, balsa, etc - even stones and fine papers.

    This is a good muscle memory technique - hope it helps.
    Keith

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