Polished on one side, coarse on the other?

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Mr.Wizard

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I have heard of a technique to supposedly get a highly aggressive edge: finish one side with a coarse stone to create "micro serrations" and polish the other to make them razor sharp. It sounds good but in practice I never got a good result, probably because I couldn't figure out what to do with the burr. Has anyone made this work better than simply finishing both sides coarse? HeavyHanded HeavyHanded Maybe your sisal wheel would work here?
 
My rather simple mind is telling me that the technique described would not necessarily work as intended. I’m imagining the teeth on the edge as similar to a saw blade, as you polish one side you will inevitably begin to reduce the distance between the peaks and troughs reducing its aggressiveness and without working the other side will bend them over. I suppose you could try to realign with the same coarse stone or a steel but not sure how effective it would be.

I appreciate this is totally over simplified but I did state I had a simple mind...
 
I've tried this, with two results.
First it makes it tough to remove the burr from the coarse side - it can be done but is not simple.

Second, the finish winds up a hybrid of the two. Say you used a 180 grit on one side and 1200 on the other, the resulting finish cuts like a 700 grit edge.

For powered setups this might hold more promise. Father in law told me he visited a scalpel manufacturer back in the 60s, 400 grit on one side, polishing wheel on the other.
 
Never tried this myself; it's an interesting idea. It seems like it'd be easier to start with the polished side to full completion, with a detectable burr leaning to the opposite side. Then do the coarse side to a complete burr, after which most of the burr could be removed from the polished side by very light abrasion (a very firm/hard loaded strop of wood, for example), as opposed to flipping the burr back & forth and worrying about excessively altering the coarse side's finish in the process.
 
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I also have a simple mind that says, "does not compute, does not compute, error, error"!! I would think that the actual apex of those two facets is going to be either one or the other. For example, if you sharpened one side at 120 grit, and the other side at 1200 grit, the very apex is going to be either 120 or 1200 grit. Which one is it then? I would think that the finish level at the apex would lean heavily toward the coarser of the two. I really don't know, tho.
 
I found a blog of a Japanese wood worker testing this.
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His conclusion was that it works well for a plane (but it was more like JIS #1,000/10,000 hybrid).
The guy claims that he was able to whittle out a 2.5 micron slice.

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I guess you can read it with Google Translate.
seisakunohibi.blog.ss-blog.jp/2010-12-10

I tried it myself but gave it up because deburring was difficult.
 
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samuraistuart samuraistuart If the abrasive were able to cut perfectly without deforming the metal it should be like actual serrations, with the scratch grooves taking the role of the scallops. In this manner ground serrations could be thought of as an edge with two "grits" at once. I don't know if abrasive grains can actually approximate that however.
 
What I typically do is SET a coarse scratch pattern with a coarse stone and then lightly hone with a fine stone, such that it removes the burr but doesn't erase the coarse scratch pattern. This works very well with my scythe blades and after several fine honing sessions I'll reset the coarse scratch pattern again.
 
FortyTwoBlades FortyTwoBlades Are you using the finer hone at the same angle, or raised i.e. micro-beveling? Which stones are you using? (Does coarse mean Manticore, or Bull Thistle, etc.) Is there asymmetry to your honing, or are both sides the same?
 
Both sides the same. Typically using the Bull Thistle and then Arctic Fox, but I use the approach on other tools as well with the relative grits being adjusted to the application of the tool.
 
FortyTwoBlades is maybe similar to how I approach it. I'll use a very coarse stone, anything from 80 to 240 or so, and lay in a microbevel with a much finer stone, just a few passes per side. This thins the cross section width but retains a lot of the along edge variation.
Only steeling does a better job but is a lot less reliable with the outcome. As with steeling I can maintain this edge a bunch of times on a hard strop before having to take it back to a stone.

To be honest, this is how I do all of my knives in general except for dedicated choppers and woodworking tools. I still finish with a micro on my finest stone, the difference is in how fine I take the set-up finish, this determines the amount of residual along-edge variation from a ton to essentially zero.
 
Mr.Wizard said:
Is that usually Suehiro G8, edge-trailing?
Click to expand...

Toss up between that, the Norton 8k, Suzuki Ya 8k, DMT EEF, and depending it might be any of my EF comparable diamond plates.

In a hurry or just because, I will still use any of my mid range stones for the full bevel and give it a couple passes on a hard strop for a similar effect. I still like my Norton Crystalon for that.
 
I set the bevel with Venev #150 and deburr on DMT EEF with a couple of very light passes.
 
Sn interesting notion, but ultimately I don't think it has any tangible value. Let's say you chisel grind serrations into a blade. It doesn't matter how much you polish the back bevel, the edge behavior will be determined by the geometry of the serrations. Same thing here. The structure of the edge, i.e how wide the apex is and how jagged or toothy the apex is will determine the edge performance. Polishing one side of the edge should have a negligible effect. That's all just theory though.
 
Obsessed with Edges Obsessed with Edges I tried your sequence using 125µ diamond microfinishing film and F1200 silicon carbide for the final stage, stropped on plain cardboard to finish. I got quite a good edge for slicing rolled paper towel. I may actually start using this. I don't know if the result is any better than it would have been with coarse on both sides and a micro-bevel, but I can say it felt smoother using the fine stone only on the polished side which at least should allow the use of a softer polishing stone without scratching it. I'm going to run this edge for a while and see how it holds up.

Coarse and fine sides with USB magnifier.

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As mentioned previously by others, I'd not be surprised if the coarse side's finish would be the dominating factor in cutting aggression at the apex itself. On the polished side, I could see the polish making some improvement behind the edge, in reducing drag/binding in tough materials. That's what's in my mind's eye, anyway. How those two opposites interplay in cutting performance, I've yet to know for myself.

I've known for some time that a polished, thin convex is scary-slick in cutting cardboard, due to the polish and the absence of hard edges at the bevel shoulders, which otherwise can bind up in tough materials.
 
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