Stropping all that "convex"?

[awestib]

Hi Knifefolks:

I once again started (another) attempt to get my convex blade knife (Fallkniven S1) sharp again on sandpaper/mousepad and later loaded leather strop and while I was getting frustrated again, I was also once again thinking about what I was actually doing. I really get the idea of a belt sander, one inch belt, rather slack, produces an elegant convex edge. But doing it by hand the way above, I don't get it. So, here are my questions:

1) I can o.k. feel whether I have the right angle with coarser sandpaper (220 or so) but the finer it gets e.g. > 1000 grit, I am getting more and more unsure. Not sure why. I can use the magic marker trick but I would like to "feel" where I am! Suggestions?

2) I understand the soft backing of a mouse pad behind the sandpaper but why the heck do we all use a loaded leather strop? Honestly guys, are we really thinking that those tough leathers are giving a fraction of a mm by the weight of a blade? I can hardly compress them with my thump never mind forming a concave "valley" with the weight of a knife!
Shouldn't we instead use a loaded cloth or something and put it on a mouse pad (since we started that way)?

3) Is the mouse pad approach a bad one after all since it gives quite a bit depending on pressure and that gives too much room for inconsistency? Should we rather use the harder (hard?) backing of a leather strop right from the start with sandpaper?

Thanks all for responds! :thumbup:A.http://www.bladeforums.com/forums/images/smilies/thumbsup.gif

 

[stitchawl]

For a convex blade, you really need a free-hanging strop (like a barber strop) rather than a bench mounted one...


Stitchawl

 

[pwet]

or put more pressure or adapt the angle or use a reglable tension barber strop, or use a softer backing under the leather. most barber strops are either reglable or have felt under the leather.

 

[JGON]

There are many factors that can impact the answers to these questions.

First of all, not all convex edges or grinds are created equal. You will need to adjust your technique and your tools depending on what you are sharpening, and what you are trying to achieve.

Secondly, not all mouse pads or strops are created equal either. Most mouse pads have enough "give" to get you a convex edge, but some are more firm than others. When it comes to myself, I sometimes question the need for a strop, but I don't do as many convex edges anymore... I mostly stick with my Japanese water stones.

It sounds like the tools you are using should work in achieving what you are trying to achieve, which means your technique might need to be refined. I know, it's hard to accept sometimes, but it seems like you are using the right tools and you understand sharpening theory, so it might just take more practice...

The best thing I can tell you is to try to be very consistent with your movements, and to always closely examine your edges, because this can help you identify any mistakes you might be making with your technique.

JGON

 

[Obsessed with Edges]

The best thing I can tell you is to try to be very consistent with your movements, and to always closely examine your edges, because this can help you identify any mistakes you might be making with your technique.

JGON

This is THE MOST IMPORTANT thing to remember, barring all else. The 'feel' aspect will only be developed with frequent practice and, until then, it's very important to closely WATCH the effect your technique has on the edge. Use good magnification (10x or better) under very bright light, to see what's going on at the edge. That'll tell you a great deal about what changes you need to make with angle & pressure.

1) I can o.k. feel whether I have the right angle with coarser sandpaper (220 or so) but the finer it gets e.g. > 1000 grit, I am getting more and more unsure. Not sure why. I can use the magic marker trick but I would like to "feel" where I am! Suggestions?

This is what I was referring to above. Use the coarse (220) grit to initially shape the bevel. After that, use the finer grits to gradually remove the burr and refine the scratch pattern (this is where the close inspection under magnification is very important). If you see the edge getting rounded off, that means either the angle is too steep (or constantly changing up/down), or the pressure is too excessive against the soft backing.

2) I understand the soft backing of a mouse pad behind the sandpaper but why the heck do we all use a loaded leather strop? Honestly guys, are we really thinking that those tough leathers are giving a fraction of a mm by the weight of a blade? I can hardly compress them with my thump never mind forming a concave "valley" with the weight of a knife!
Shouldn't we instead use a loaded cloth or something and put it on a mouse pad (since we started that way)?

By the time you get to the strop, your pressure needn't be hard at all. In fact, it should be very, very light. No need to try to form a concave 'valley' in the leather. Whatever polishing of the bevel is done here, should be done very gently. And at the very edge itself, pressure should be absolutely feather-light. The assumption is, the edge is already very fine BEFORE the strop is used. The strop is intended to straighten or remove any fine burrs that might be left, and very gently polish the bevel & edge. The strop is all about refinement of an already fine edge. That needs to be done very gently & carefully.

3) Is the mouse pad approach a bad one after all since it gives quite a bit depending on pressure and that gives too much room for inconsistency? Should we rather use the harder (hard?) backing of a leather strop right from the start with sandpaper?

This is all about preference, and is greatly influenced by experience which, obviously, takes time & practice. The 'inconsistency' you mention, is something that will go away with time, as you develop the feel for it.

 

[Super X]

I don't know if this will help but will tell you anyway. When I started learning this technique I went and bought a thick mousepad. This was bad, as it allowed too much rounding off I believe and I was using too much pressure. My leather for my strop is mounted on a 1 x 6 oak board, I started using my strop as the backer instead of the thick mousepad and got better results immediately. Maybe your mousepad has to much give and you need a harder backer. The other thing is go easy on the pressure. Once I get my blade where I want it, I go to the black compound and strop, then finished with the green or plain leather. Hope that helps, sorry if it does not, but sounded similar to my first experiences.

 

[awestib]

Thanks guys, that all actually helps quite a bit. I will start to observe the edge with magnification more as I sharpen along and I might consider a harder backing.

Andy

 

[Gadgetaholic]

I convex most of my blades and strop them on a paddle strop. I bought a double sided paddle strop, but prefer the home made ones I used a broken belt to make. 95% of the time a strop is my only sharpening device I use, once the bevel is set how I like it I can maintain a nice sharp edge with regular use of a strop alone.

 

[Obsessed with Edges]

I'll also second (3rd?) using leather as a backing, instead of a mousepad. This is my preference. The mousepad idea always struck me as a bit too thick & soft. This is what I was referring to earlier, in pointing out that the backing used will be influenced by some experience in trying different things out. I use one of my regular home-made strop blocks, with leather that's about 1/16" thick. And, for what it's worth, I'm now beginning to give some thought to going even thinner, perhaps to a hard backing ultimately.

 

[bkzk100]

a basswood block with a groove cut into it by a rounded carving chisel and loaded with buffing compound has been used for years when sharpening your gouges. ive moved on to a rectangular block loaded with compound for final stropping and it works fine. you can get a bag of basswood for around $5 at a craft store.