stropping causes fragile edge?

B

biogon

Joined
Jan 2, 2002
Messages
2,111
I've been getting weird fragile edges on my knives, and I don't know why.

I sharpen on an EdgePro and take it to the 600 grit at around 20-21 deg per side. I'm not adventurous enough yet to take them down to the 15-18 degrees yet.

Makes a rather nice edge, but not as good as with a final strop. I strop on a leather belt with Maas/Flitz metal polish. It has worked beautifully until recently.

I have been getting very sharp, ultra-fragile edges recently -- they glide through paper on their own weight (with a slicing action), but on 2 and 4 ply cardboard, they microchip -- just like a wire edge. Originally smooth to the touch, they get these little bumps and ridges after going through about 2-3 li. feet of cardboard that are actually visible.

I know I've removed the burr and the wire edge correctly, because the blade isn't fragile when it comes off the 600 grit hone, just after stropping. I use Joe T's technique of putting in a tiny secondary bevel to clean up the burr.

Then, on the strop, I usually make 3-4 passes at moderate pressure to clean up the bevel and edge, and then 1 pass at very light pressure (knife weight or less)

I can't imagine I've changed my technique; what am I doing wrong now?

Thanks!

-jon
 
yikes.. what kind of steel is chipping on you?? i have a henckels kitchen knife that microchips so bad that it almost has a "spyderedge" instead of a plain one. on the other hand, my 154cm & s30v blades seem to hang tough no matter what.
 
So far, 154CM, 12C27 (or whatever the Swedish steel is) and 8670 (non-stainless carbon)...

I don't understand why it's doing it now, when it didn't do that before...

Maybe the strop is dirty? Maybe it needs to be cleaned? Maybe I'm using too much pressure? Maybe the metal polish is cutting too strongly?

Very weird...

-j
 
If it used to work, and now doesn't, something must have changed. If stropping didn't used to give you this problem and now you have the problem it is not simply that stropping causes weak edges.

If this is the same knife that used to work and now doesn't and your technique used to give you good results on this knife there must be a long term problem with your technique. There must be something a little wrong with what you have been doing and now it has accumulated to be a noticeable problem. I would guess that you have been only marginally removing your burrs with your honing, but your honing technique leaves a well aligned and healthy burr. You are only doing a few stropping passes and don't remove the burr, just flop it back and forth causing work hardening and fatigue in the burr. Now the burr fails easily. If this hypothesis is true you need to microbevel edge forwards at about 45 degrees (double the angle that you normally use) per side using about 5 very light strokes per side (alternating). Then resharpen about 5 strokes per side at your normal angle. Be sure you are always using edge-forwards honing strokes to reduce burr formation. You may also find it handy to do a few more stropping strokes to remove burrs as well as align your edges.

If this is a new knife, all bets are off. Some don't seem to like to be stropped.
 
my guess is that you're not stropping enough....you may be pushing the wire edge up to the center w/o removing it.......also, i would recomend using more presure on the strop......what kind of compound are you using on the strop?...i recomend using only coloring compounds for final stropping....keep us posted
 
Jeff,

Ahhh... it has been happening on both old and new knives. Perhaps it's a combination of both... The 8670 (a Greco, not surprisingly) never liked stropping -- always had this problem. It's my BM 520 (154CM) that started showing it.

I usually only do 1 microbevel/burr removal pass per side, and usually only a few degrees steeper than the edge is set at. I'll try your technique with 5 passes each side at twice the edge angle followed by 5 more passes at the original angle.

Perhaps I've started skimping on the burr removal steps recently and didn't notice it...

I find that if I strop for more than 4-6 strokes, my edges get dull (i.e. not matching the angle perfectly, I guess)

Thanks much!

-jon
 
skintback,

Good idea, I'll try adding some pressure.

Believe it or not, I've been using Maas or Flitz. It seemed to work pretty well so far, and sadly it's the only stuff I can get locally. I'm afraid it might be too abrasive?

One of these days I'll have to order some proper stropping compound, but I hate having to pay equal s/h to the product cost. ;) Any recommendations?

-jon
 
I've never seen the need to strop on anything other than the backside of an old leather belt myself.
 
Originally posted by biogon
I've been getting weird fragile edges on my knives, and I don't know why.

I have been getting very sharp, ultra-fragile edges recently -- they glide through paper on their own weight (with a slicing action), but on 2 and 4 ply cardboard, they microchip -- just like a wire edge. Originally smooth to the touch, they get these little bumps and ridges after going through about 2-3 li. feet of cardboard that are actually visible.
Click to expand...

Hold on a moment please.............

This might not be a problem with your sharpening at all
(isn't this what you wanted to hear? :D)

Corragated cardboard is notoriously hard on knives because they contain a lot of dirt, grit and other undesirable abrasives - so it will blunt knives very quickly.

I had a similar experience cutting a sisal rope off of an old rope floor mat..... that became obvious the rope was loaded with dirt and grit - and it didn't matter if it were cut with a humble SAK steel or a premimum steel like on the Sebenza - the blade was going to blunt after only a few cuts - please see this thread:

Rope Cutting

and this thread might be relevant:

Polished vs. Coarse edges
 
sounds like your sharpening angle may be the problem. I strop all my knives with no problems at all with fragile edges.
 
All the ideas you've gotten sound good. Jeff is the man - I'd look into his first.

FWIW I remove the burr by dragging the blade cross grain on hardwood. Then I strop. The idea is that if the steel is weak it's gonna come off sooner or later - and before stropping is better than during use. Both the burr itself and the steel supporting it can get weakened by the sharpening process (as Jeff points out), so get rid of it. Does that make sense? Stropping is going to remove some of the burr, but (in my book) won't remove all the weak steel. Final stropping, then, restores the edge without re-creating a burr.

For brand new knives I:

Do the above process
Hack at a piece of wood like an ax
Inspect for chips in the edge
If perfect, then Re-strop and ship

Even fine edge kitchen knives at 17 degrees should be able to pass this test.

Steve
 
hey biogon,
check the local large hardware stores, some sell a sample pack of 4 different buffing compounds for a few dollars.....the black compound is the coursest...i use it after my coursest abrasives for a very toothy edge...the white is the one you will use the most...even after using the black compound, i finish w/ the white....for surgical edges, i go to surgical stones, then finish w/ the red "jewelers rouge".....i only sharpen to a single angle, and strop off the burr that i get.....follow the same angle as you sharpened at, and work both sides till the burr is gone....you may find you want to stop at a courser grit to give the edge more bite on a slice than a slick polished edge
 
skintback,
I don't have access to that kind of stuff (the 4 in 1 pack) or anything else remotely close over here. KNow where I can get it online, or, if you can help me get it?
thanks
 
sounds like the burr is not being completely removed before stropping.
 
Originally posted by UnknownVT

Corragated cardboard is notoriously hard on knives because they contain a lot of dirt, grit and other undesirable abrasives - so it will blunt knives very quickly.
Click to expand...

This is true.

I suggest using a finer than 600 grit stone before moving to the strop.

Also, don't use Flitz. It doesn't do anything. Flitz polishes CHEMICALLY and only has the tinyest amount of mild abrasive. Once it's dry it's practically useless and it's useless on a strop in all accounts. What you want is a block of white polishing compound found by the car-polishing wheels at your local Sears. It's best to apply a strop-conditioning paste first and then apply the compound like a crayon.
 
Originally posted by fulloflead
This is true.

I suggest using a finer than 600 grit stone before moving to the strop.
Click to expand...

This is my suggestion too. Only as an experiment.
I use an Edge Pro and if you sharpen normally with 600 and then go immediately to the 3000 polishing tape, you will NOT raise any burr.
Do NOT strop but start using the blade and check for chips.

This will tell you if it is technique or a blade that has been badly tempered or has internal damage/stress.

Also another point that has never been raised yet.
The Edge Pro angle is measured from the hone to the table.
This means that an EdgePro angle of 19 degs is actually 17 degs ( 34 Included )

This might be worthwhile info if you were using EdgePro angle of 15 degs, where you would in reality have 13degs, a little narrow maybe.
 
My impression is that burr is not being fully removed.

I do believe that stropping will remove a burr if enough strokes are performed in each direction.

An easy method would be to "steel" (on a smooth steel) taking several light strokes on both sides of the knife at a slightly greater angle than you sharpened at. This quickly removes the burr and then aligns the edge for super sharpness. Many people don't buy this when they first hear it but give it a try and form your own opinion before passing judgement. You can then go to the strop for a polished edge is you desire.

Another thing I'll mention, and this probably has little to nothing to do with this particular problem you're having, but try to make sure to sharpen in a proper relief and use a dual beveled edge.
So many people sharpen their knives using only one angle all the time over and over again only to find that their knives just can't get as sharp as they once did. They never consider the fact of proper edge relief. If an edge is first sharpened to a bevel of 15 deg and then a primary edge is put on at 20 deg this will give you a properly relieved edge that has enough strength to deter knicks and maintain sharpness for a sufficient amount of time while performaing most comman cutting tasks.

Anyway, just my .02 cents...

--The Raptor--
 
It could be that your stropping is simply pushing the edge back and forth, which weakens the metal and might cause it to eventually break. It's like if you take a paper clip and bend it back and forth: after awhile, you can just snap it in half with little effort.

Sharpening with a good abrasive material doen't cause this weakening because metal is actually removed from the edge. If you sharpen with stuff that isn't very abrasive (ultra fine stones, a smooth steel, uncharged strops), then you may aline the edge, but you don't remove weakened metal from the edge.
 
You must log in or register to reply here.
Back
Top