When to strop?

M

mordi

Joined
Aug 12, 2007
Messages
137
Hi I use a belt sander for sharpening.Usually I start at 120 then240,,400,
20mic, 9mic. Then strop with leather and green compound, then bare leather.
Finally I put a very small micro bevel with a fine ceramic.
A few posters on this forum say that when going from 400 grit directly
to leather they get sharper blades with better edge retention.How would
a large scratch pattern on the edge accomplish this?
This is not a criticism I'm just trying to understand,thanks.
 
i have found the edge to be a little toothier sort of like mini serrations. going by feedback from guys i sharpened knives for when i sharpened by hand, they liked the edge put on with a ceramic stick rather than a highly polished super fine edge like what you would get from the micron belts or similar. they said the super fine edge was wiped out fairly fast even on a good knife. on my personal knives that i make or light duty knives, i polish the edge with a worn 400 grit belt. i finish up on a slotted paper wheel to remove the burr.
 
Good question. I'm hoping there are plenty of responses to this one. My belief is that the toothier edge uses two cutting modes, pressure and friction. The finer edge only uses pressure (for the most part). Within the edge on a coarse grind you have points between small scallops. The scallops are somewhat protected by the teeth, and the teeth themselves do some cutting via friction. It takes a lot of use to both wear away the teeth and dull the scallops. Even when these are fairly dull they'll continue to cut with friction alone due to the relatively uneven edge surface. Another consideration, with a coarse grind there is a longer cutting edge due to all the irregularities.

With a highly polished edge, there is a virtually uniform cutting edge, with a smaller terminal cutting surface. Initially this will cut extremely well, but it is also more susceptible to edge deformation and wear. Should it come into contact with tougher materials there's less surface area to absorb impact stresses, and anything that dulls the edge will degrade performance faster because the cutting edge has no valleys or mountains to protect some parts of the edge, or provide a mechanism for cutting by friction. It'll cut better on most materials, but require considerably more maintenance to function at that level.

That's my take.
HH
 
A toothy edge will tend to display sharpness far beyond its actual ability. For example, it may grab at your thumbnail or slice paper in its serrations even when the actual edge is not particularly sharp. I find that as the edge gets more refined, the 'display' of sharpness goes away as the micro serrations are lost.

This being the case, a polished edge may lose the ability to 'display' sharpness quickly, but due to its sharpness and geometry it continues to cut well. The toothy edge looses its ability to cut very quickly, but still 'displays' sharpness, so it is assumed that it still is.

I used to sharpen my kitchen knives to a toothy edge, and they would cut well but only for a short period. Now, with a more refined edge, they cut better, longer, even though they don't display sharpness in a test like a toothy edge would. If you compared the two of them, the one with the refined edge may appear "dull" in a test, but will actually cut considerably better than the toothy one that appeared "sharp".

All these are just my observations regarding a toothier edge vs. a smooth one, I don't use a 400g belt and leather on anything, so can't respond to that combo specifically. Also, I would imagine that some materials to be cut could change the way that any of this is perceived (rope vs. a bell pepper).

ETA... Looking at your other post, you probably have much more experience with kitchen knives than I do. Don't worry too much about what 'other people say', while they are not necessarily lying, it doesn't always mean what you think it does. If they tended to get a burr when they sharpened to a fine edge, but didn't when they sharpened to a coarse edge, then they could be convinced that a fine edge instantly rolls over and looses its edge. Or if they lost the edge while stropping, they could be convinced that a fine edge is actually dull, while a coarse one is sharp. In both those cases, it would be the truth to them, but still not necessarily correct. I am not pointing out anyone in particular, just showing that just because someone honestly believes something doesn't make it the truth...myself included.
 
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HeavyHanded said:
With a highly polished edge, there is a virtually uniform cutting edge, with a smaller terminal cutting surface. Initially this will cut extremely well, but it is also more susceptible to edge deformation and wear. Should it come into contact with tougher materials there's less surface area to absorb impact stresses, and anything that dulls the edge will degrade performance faster because the cutting edge has no valleys or mountains to protect some parts of the edge, or provide a mechanism for cutting by friction. It'll cut better on most materials, but require considerably more maintenance to function at that level.
HH
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My expeience with highly polished edges is different. I find they are less susceptible to edge deformation. Wear is another story, due to there being less surface area to spread cutting out over, thus equating to more exposure and wear. It seems to me that with a high polish (and therefore less surfce area) the edge is stronger due to there being fewer irregularities, ie. "valleys and mountains", which are less stable due to there being less steel surrounding them (the peaks/points/microserrations, that is) to support them.

Although, if you look at it another way, there is less overall steel with a highly polished edge, and therefore, in theory at least, it should be thinner and consequently less stable.:confused:

Who really knows, though. I've had chips and rolls with both utility and polishd edges (thoughly seemingly less with polished). There's bound to be alot of conflicting theories and "evidence" on this matter. Knowledge questioned, egos bruised, tempers flared... should be good.
 
Any cal & Karl, excellent posts and my thoughts exactly.... well kinda ;)

The blade geometry, steel and it HT, and the edge shape you apply will sometimes be larger factors. You can have a completely dull and dented convex, thin hollow or thin FFG and the will still cut like a sharp knife... Why? because they have good cutting geometry to begin with.

Sometimes sharpness is not even a factor in a knifes ability to cut.

When it comes to the edge though I feel that proper form and flow make up most of the performance. Using a high quality abrasive is also another contributing factor to the quality and longevity of your edge.

The toothy edge is not toothy in the way most people think. The teeth you feel on the edge are a result of the size of scratch the abrasive makes. The teeth themselves are bits of excess metal that have been dragged to the edge. This is plastic deformation, these deformed bits of metal that make up your "feel" of sharpness are the first thing to wear when the cutting starts. I personally feel that when the edge is refined to a high grit and free of edge deformations that the material being cut can only effect the steel and the edge shape. I want my knife too cut because it is sharp not because it has teeth.

To the OP, why would you polish a edge to 50,000 grit then microbevel with a average 1200 grit ceramic rod? Your taking about 48,000 grit of sharpness away from your blade and without doubt creating a burr again. After your belt stropping the edge should be sticky too the touch and be ready for the morning shave. If you still want to microbevel use a spyderco UF SM rod followed by a hard surface strop with QUALITY 0.5 micron compound.
 
What I find most interesting is the differences in reported edge retention between the two types of grind. Maybe as you have pointed out, the quality of the grinding media has a lot to do with this (when comparing different edge preparations on the same knife). In my opinion, the teeth are not a plastic deformation, rather they're what's left after the steel on either side has been removed, and this may have a lot to do with the material doing the grinding. In any event, isn't a certain amount of plastic flow (deformation) required to achieve a hair whittling edge? Another thing needed in the conversation is a consistent definition of how coarse is coarse, and how fine is fine.

My own experience is that the coarse edge will outlast the fine edge two to three times over. I say "in my experience", YMMV. I'm working in a printing shop, typical diet is heavy paper, clay-coated paper of all weights, plastic crate banding, tie-raps, small gauge wiring, and of course plenty of cardboard as well as the incidental contact with metal press parts. Under these conditions a fine edge (hair-popping sharp) will stop push cutting through paper in two weeks or less if no maintenance is performed, and will have a hard time shaving hair off an arm in a week or less. I noticed (after much trial and error) that a very coarse edge will perform much better here, needing to be touched up only every month or two, if even this often. It may be something of a saw edge, but it will, even after heavy use, still cut free-hanging denim with an energetic swat, easily part plastic clamshell packaging (as well as cut my apple for lunch), and instead of needing to be stropped or honed every couple of days, it needs only to have any adhesive reside washed from its grind. I know this topic will likely never be resolved, but I am amazed at the very different experiences folks are running into. Blade steel, edge geometry, edge grind, material to be cut, cutting technique etc etc. As I've said before it's like jumping down the rabbit hole. One size does not fit all.
 
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+1 heavyhanded and an even better post on what you said about the wire thin edge not lasting long, not to mention taking UP TO 8 HOURS TO ACHIEVE on a 4" knife when done on diamonds. i relied on the feedback over many years of sharpening knives for other people plus feedback from knives i make.

guys who use their knives for more than whittling hairs told me the wire thin edge i used to put on their knives didnt work out for cutting items like yoiu mentioned. they like a more toothier edge on their knives just like you do. i can put a hair popping edge on a knife and not have to go down to 1/2 a micron grit in order to attain that edge.
 
Grinding on the edge is plastic deformation, the abrasive contacting the metal cuts a groove in the surface of the metal, this groove will have peaks and valleys caused by the abrasive. Its a deformation of metal from the shoulder to the cutting edge. If you take a piece of plastic and drag a awl across the surface you create a groove with raised peaks, this is the same thing that happens to your bevel when grinding with a abrasive.

If the abrasive is hard enough (diamonds) then it is very possible to have a coarse grit edge with no deformation/burrs at the edge. When I talk coarse though I mean no higher than 300-400 grit, when you go higher the table turns again and it a whole new ball game.

not to mention taking UP TO 8 HOURS TO ACHIEVE on a 4" knife when done on diamonds.
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Before you make comments on subjects you know nothing about you should really think about what your saying. 8+ hours is for a fully hand polished edge, I'm not spending 8 hours on the stones. If you want to talk about speed of touch-up then I bet my way is faster, it takes about 4 swipes to touch-up a knife on a finishing diamond hone and if I just want to sharpen its only about 10-20 minutes. So before you go putting thing's in BOLD get your story straight.
 
it takes me a few seconds to touch up a blade and under a minute to completely sharpen a dull one.
 
HeavyHanded + 1 , Richard J + 2 . This echos Joe Talmadge, John Juranitch and my findings as well . This will never get resolved and thats ok to each enjoyment, his own .
Wasn't the OP about when to strop ??? O-well we tread a lot of ground here . DM
 
American Heritage Dictionary= Cut

VERB:
cut, cut·ting, cuts
VERB:
tr.

To penetrate with a sharp edge; strike a narrow opening in.
To separate into parts with or as if with a sharp-edged instrument; sever: cut cloth with scissors.
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Sharpness will always be a factor in a knife's ability to "cut"

If your knife is dull you are not so much cutting as you are plowing through something.
 
after seeing people fly into each other's hair in the previous posts, I guess my advice would be to do what most of us do or have done:
experiment for yourself and check the statements made here on the forums for validity and for things you can use. Your experience, use and common sense will make you progress rapidly. Try seeing what happens to the edge with a magnifier when you do different things and in the end you'll achieve the things YOU want to achieve.
 
5.56 said:
Sharpness will always be a factor in a knife's ability to "cut"

If your knife is dull you are not so much cutting as you are plowing through something.
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What are you a cross between Sharp Phil and Josh K?

OK to play your silly game, look at the fifth definition from your American Heritage Dictionary citation - sever. Makes no reference to a sharp instrument :rolleyes:
 
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