Stropping problems

[chuckasher55]

I sharpen my knives on a 1x30 belt sander, knock the burr off with a paper wheel and they usually are then shaving sharp. I then VERY lightly run both sides of the blade (one pass only on each side of the blade) on a leather belt loaded with green stropping compound and there is usually a noticeable improvement in the blade's sharpness.

However, if I use the leather belt more than once per side the blade gets dull (often it will not cut paper afterward). Also, if I use a manual strop my blades always get duller. I have watched many YouTube videos on stropping and read step by step instructions as well. Nothing works.

I would really like to learn to strop effectively to both refine the edges and also to do knife edge maintenance so I could minimize how many times I need to sharpen. I want to learn manual stropping but also want to learn to use a stropping belt properly.

Any suggestions about what I may be doing wrong?

 

[willc]

Light pressure and don’t bring angle up high enough to round edge.
Also when I get into real high grit stropping a super light touch gives me best results.

 

[Baron Mind]

Almost certainly your issue is you're rounding your apex. If you slip and raise your angle too much you're then just scraping your crisp apex along a hard surface, which is about as bad for an edge as it sounds.

If you stay on angle but press too hard, the strop compresses, your apex is then digging into the strop, and rounding off your apex.

Try lowering your angle a hair, and/or not pressing as hard.

 

[Eli Chaps]

If you don't strop, how long does your edge last off the paper wheel?

It could be that you're developing a fine wire edge (burr) off the wheel and that will be quite sharp, but it will also be quite fragile. So the stropping may be removing the burr, as they are intended to do, so it then becomes duller.

The problem might be further upstream from the stropping.

Just a thought.

 

[Bill3152]

One thing I learned from using paper wheels is if you have to strop after using one you weren't finished.

 

[Obsessed with Edges]

If the edge is dulling after only one or two passes per side on a leather belt with green compound, something's definitely not right. A strop of this type wouldn't ordinarily be aggessive enough to degrade a sharp edge that quickly. Something else is going wrong, such as:

1. Weak & ductile wire edge or burr that's immediately folding over with the one pass on the strop. The folded burr will mimic a rounded (dulled) apex. Even so, if the edge geometry (angle) is thin enough, such a weak burr folding over won't have as profound an impact on cutting as it seems here.

2. Edge isn't fully apexed from BOTH sides, but perhaps just one side, and there's a wire or burr left there which mimics sharpness until it's removed on the strop, leaving incompletely-apexed geometry behind.

3. Edge angle is much too obtuse or rounded to begin with, leaving poor cutting geometry behind after the 'sharp' burr is removed. If the edge angle is much beyond 40° inclusive, it'll be much more challenging to leave a perfectly sharp & crisp apex after the burr comes off.

4. It's also possible the belt grinder is rounding the edge geometry, if there's too much slack in the belt. The grinder can still leave a sharp burr (belt grinders are very good at this), but the geometry behind it may be too thick or rounded.