Sharpening tips

[alexwang32]

I've been freehand sharpening my cheif's knife for a year now and have gotten quite good at it. I use sandpaper to avoid the hassle of having to flatten whetstones now and then. I start with 600 grit and go up or down depending on the dullness.

Now, my cheif knife is relatively easy to sharpen, it's made of a bright stainless steel. It doesn't take too many passes to get a burr, especially using 220 grit, I get it up to 3000 in less than half an hour. But this is the only knife I can sharpen with ease. Comparatively my other small paring knife is a nightmare to sharpen, I always have to start with 80 grit and give it 50+ strokes until it finally forms a burr ( yes I feel for the smallest raised burr, not a big burr ). What makes this knife so hard to sharpen? (a better question is what makes it go dull so badly, considering I don't use it for anything else besides paring tomatoes and apples).

Other blades that requires tons of elbow grease and time include my woodworking hand planer blades, while I watch people online sharpening using only a few strokes, mine take half an hour on the coarsest grit... I'm really considering switching to a belt for those.

Another thing, I see some people continue sharpening their blades using a finer grit even after it has raised a burr, and finally get rid of it from the other side when they've finished. How does this method compare to removing the burr every time it raises before continuing with a finer grit? I believe the first method involves raising a bigger burr.

 

[Obsessed with Edges]

Lots of questions and possible issues with the paring knife sharpening. Unless that blade is extremely thick, which is odd especially for a paring knife, 80-grit should be way too coarse for it. I wouldn't consider going below about ~150 or so, assuming it needs a lot of thinning anyway. And for upkeep sharpening, nothing below ~320 or so should be necessary for such a small blade. Upkeep sharpening on a paring knife should ordinarily be about as simple and quick as any sharpening task could be.

And with the sandpaper, if it's not tightly affixed (glued, etc) to a hard surface (stone or glass), it may be lifting or rolling/curling around the apex of the edge, which could round it off and make it difficult to form the burr in the first place. That'll be made even worse if the blade is really thick as I mentioned above. That may be another complication.

The other thing with sandpaper is, if it's SiC (silicon carbide) wet/dry paper, the grit will tend to break down pretty fast, which makes heavy grinding much slower as you go. And clogging of the grit with metal swarf will slow it even more. Especially with grinding very wide-bevelled edges (planer blades), the work can get excruciatingly slow on sandpaper. Heavy grinding is best done on a lubricated stone (SiC, diamond, waterstones), or an aluminum oxide sanding/grinding belt cut and laid flat (glued) to a hard backing also works pretty well for that. Something around 150 - 220 grit works very fast for that.

It would be helpful to know the steel type or brand/model of the paring knife. Also, posting a pic or two of the knife might be helpful in generating some more specific advice for getting it done.

 

[eKretz]

Some knives aren't hardened to a very high hardness; they will dull rapidly. Knives that take a long time to set a new bevel on are candidates for thinning behind the edge - if you're doing your sharpening properly. The thicker they are here, the wider the bevel is and the longer it will take to remove enough material across the entire surface to raise a burr.

Edit: O.W.E. posted whilst I was typing, I agree with his positions too.

 

[Wowbagger]

What makes this knife so hard to sharpen? (a better question is what makes it go dull so badly, considering I don't use it for anything else besides paring tomatoes and apples).

Let me guess . . .
you use a marble cutting board.
This knife has gone a year and a half with zero sharpening used on much fruit and vegetables and opening packages like crackers and cereal.
The "secret" ? Good steel but not expensive, superior edge geometry and a super forgiving softish plastic cutting board. It's still shave sharp (it was hair whittling six months ago).
I might sharpen it tomorrow but it is perfectly serviceable tonight.
Sharpening method ?
Edge Pro Apex of course.
50 strokes ?
I could take a dull, dull, knife to polished edge in 60 TOTAL strokes on the Edge Pro.
220, 500, 1000, 4000 done.

 

[Wowbagger]

woodworking hand planer blades

This was all hand planed. Zero power tools. Zero sand paper.
Bubinga no less.
I swear by my Varitas jig and Shapton Pro stones
Don't fear the flattening of a water stone it is about the easiest thing I have ever done except maybe catch a cold.





Mirror finished end grain right off the blade (I love my sharpening jigs !)

 

[Wowbagger]

raised a burr, and finally get rid of it from the other side when they've finished. How does this method compare to removing the burr every time it raises before continuing with a finer grit? I believe the first method involves raising a bigger burr.

Good steel, great sharpening jig, super Shapton Pro stones = very little bur and no big deal to get rid of it with a few stones (no strops ((strops suck))). By the time I am finished with the stones shown and often I don't use all of them just three or four the bur has been reduced to the finest, thinest thing and comes off on the last stone looking like micro fragments off a single human hair. Takes practice and ATTENTION TO DETAIL ! ! ! !
But with the jig it gets very, very, very easy. Got to pay attention to what you are doing on the very edge of the blade though. Get a jeweler's visor and LOOK !

 

[Obsessed with Edges]

Another thought about the 80-grit used for the paring knife...

One reason I never like going that coarse for sharpening is, the edge really gets beat up and is left ragged from using such coarse grit. Two problems coming out of that are (1) the edge will need a LOT of cleaning up & refinement afterward, and (2) any of that beat-up, ragged steel left behind will be weakened by the 'bludgeoning' effect (as I call it) of the coarse grit against the edge. I equate the damage left behind to using thousands & thousands of 80-grit-sized ball-peen hammers against the edge. The ragged & weakened steel left behind will be prone to folding over and rapidly dulling the edge, if all of it isn't fully removed with a finer grit progression. That could explain, at least in part, why the edge dulls so quickly after sharpening, assuming there aren't other factors contributing to that as well (hard/abrasive cutting surface, etc). All of this is made even worse if the steel is relatively soft, inexpensive stainless; I have a paring knife like that, bought at the grocery store for a few bucks, and it won't hold an edge very well anyway, even on it's best day.

So, again, lots of possible issues and questions about what's going on. Filling in the details should help in figuring it out.

 

[Eli Chaps]

With 80 grit sandpaper and that many strokes over who knows how many sessions, I can't help but wonder if that pairing knife's "edge" isn't getting up into the thicker blade stock. Most pairing knives have very short bevels.

But there's just not enough info to give solid input. Very well could be that the knife is truly junk steel. But then again, it could be something high-end.

 

[alexwang32]

Wow a lot to take in here, here's to sum up what's being said

• Pros use stone and diamond boards exclusively, sand paper is not used because a) it dulls quickly b) it gets covered by metal debris fast, further slowing down the grinding process ( Would constantly washing off the metal shaving help? How do stones make a difference?) and c) without proper adhesion it doesn't lay completely flat
• 80 grit is too coarse for sharpening
• Good sharpening jigs speed up the process

I suppose I should post some more detail about my problem. I don't want to use 80 grit, I can see how badly it scratches the bevel, which is why I do take plenty of strokes on 220 afterwards to even it out, then move up to 360, 600, 1000. But somehow I just can't get a burr on certain blades without spending half an hour using 220, with the paring knife being one of the notorious ones. Now it seems that the sandpaper I'm using may be at fault.

Here's my current technique: When I sharpen I feel for the existing bevel angle and maintain it by eye and feel, trying not to raise a burr quickly by increasing the angle slightly, I take as many strokes as it takes to raise a the smallest burr felt by the finger nail. I've had success sharpening chisels, it takes less than 5 minutes for me to sharpen a used dull one, but planner knives take very very long (half an hour) using 220 grit. It drives me crazy, I think I might be doing something wrong since I see professional woodworkers like Paul Sellers sharpen with ease.

As for the paring knife( https://photos.app.goo.gl/y7KzbQb4BhuUY3Zt9), I use it mainly for peeling, I chop it occasionally on my bamboo cutting board. Currently I can get a burr on the tip and end but the middle section fails to raise a burr, what's the best thing to be done in this case?

I know too many questions in one thread is not a wise, but I'll squeeze another one in: I've sharpened some plastic handled scissors around the house, they get sharp alright, but never quite to their original sharpness. I had a small thread cutting scissor for tailoring work, I sharpened it all the way up to 2000, but the shearing action is gone, just two sharp blades passing by each other. What could have gone wrong? My speculation would be either the angle of the blade (a 80 bevel has more shearing action than a sharp 50 degree, even though it's inherently duller), or I failed to sharpen all the way to the rivet holding the two blades together, hammering the rivet in this case was of no avail. One of the scissor did see improvement in cutting, though it won't cut to the tip, that one probably had its "set" ruined somehow...


Thank you so much for your expertise on these, as you see I've spent many hours in agony, browsing online only to find very few detailed and specific answers, after all the art of sharpening is know to only a few people these days.

 

[Spideyjg]

80 grit is to thin the steel. Don't draw a burr with it. When it is getting close jump up to finer grit.

Looked at the picture and that is a junk drawer knife. Notice how the hollow grind fades as it nears the handle? The fingerprint of junk knives. They often have horrible geometry in addition to crap steel.

If you can sharpen the chef you have the mechanics down. The other will give you fits because it is not worth your time.

Scissors are not knives. Ride lines, set, and tension all come into play that don't apply to knives.

 

[Wowbagger]

Good sharpening jigs speed up the process

Not only that the shape of the wedge at the edge, (= that's as good as my poetry gets)
called the geometry, is superior so the blade cuts better / deeper with more control and for a longer period before needing resharpened.
Guuuuuurrrrrenteed.

 

[Obsessed with Edges]

I'm getting the feeling the sandpaper, or how it's being used, is the biggest limitation. The slowness of grinding (grit breaking down, clogging with swarf), the difficulty raising a burr, even at very coarse grit (edge rounding), and the loss of the shearing sharpness in the scissors (more edge rounding) all sound like issues I've seen with sandpaper, and also when it isn't completely, firmly affixed to a hard backing.

I'd suggest that you give a simple dual-grit oilstone in SiC or aluminum oxide a try; something in the 180/220 (Coarse side) - 320/400 (Fine side) ballpark. A Norton India stone (aluminum oxide) or Crystolon (SiC) is a good starting point. Being that you've been able to get some decent results with your technique on sandpaper, I think you'd get even better results with a stone. Especially in raising a burr, which should happen quite fast on a hard stone. And in refinement, the finished edge will be much crisper coming off a stone. Could solve a lot (or all) of the issues you're seeing, very quickly. Use the stone with oil, which will keep the stone from getting clogged up with swarf.

Use the stone at first to do only ONE task, which is to raise a fully obvious burr at a decent sharpening angle for good cutting. That'd be something around ~ 30° inclusive (15° per side), for really good cutting performance from the paring knife in the kitchen. Then use the same stone to flip, reduce & eliminate the burr. Do as much of that as you can on the coarser side; if done as such, everything that follows in refinement will be much easier.

I'd also suggest using something other than bamboo for the cutting board. Bamboo has a very high silica content, which is pretty abrasive against sharp knife edges. You may be getting some dulling of the edge from that. I use a white poly cutting board in the kitchen. Even 'cheap' stainless edges hold up well, used on that stuff. Or, to put it differently, if the edge gets dull, it won't be the board doing it.

 

[bucketstove]

I know too many questions in one thread is not a wise, but I'll squeeze another one in: I've sharpened some plastic handled scissors around the house, they get sharp alright, but never quite to their original sharpness. I had a small thread cutting scissor for tailoring work, I sharpened it all the way up to 2000, but the shearing action is gone, just two sharp blades passing by each other. What could have gone wrong? My speculation would be either the angle of the blade (a 80 bevel has more shearing action than a sharp 50 degree, even though it's inherently duller), or I failed to sharpen all the way to the rivet holding the two blades together, hammering the rivet in this case was of no avail. One of the scissor did see improvement in cutting, though it won't cut to the tip, that one probably had its "set" ruined somehow...

Hi,
What does that mean?

If you sharpened scissors, each blade can slice paper or shave ...
but the scisssors no longer cut as scissors,
even though the blades are touching each other as you open/close as they should?
well that means you've ground on the wrong side of the scissors,
the inside side, ...

 

[alexwang32]

I'm getting the feeling the sandpaper, or how it's being used, is the biggest limitation. The slowness of grinding (grit breaking down, clogging with swarf), the difficulty raising a burr, even at very coarse grit (edge rounding), and the loss of the shearing sharpness in the scissors (more edge rounding) all sound like issues I've seen with sandpaper, and also when it isn't completely, firmly affixed to a hard backing.

I'd suggest that you give a simple dual-grit oilstone in SiC or aluminum oxide a try; something in the 180/220 (Coarse side) - 320/400 (Fine side) ballpark. A Norton India stone (aluminum oxide) or Crystolon (SiC) is a good starting point. Being that you've been able to get some decent results with your technique on sandpaper, I think you'd get even better results with a stone. Especially in raising a burr, which should happen quite fast on a hard stone. And in refinement, the finished edge will be much crisper coming off a stone. Could solve a lot (or all) of the issues you're seeing, very quickly. Use the stone with oil, which will keep the stone from getting clogged up with swarf.

Use the stone at first to do only ONE task, which is to raise a fully obvious burr at a decent sharpening angle for good cutting. That'd be something around ~ 30° inclusive (15° per side), for really good cutting performance from the paring knife in the kitchen. Then use the same stone to flip, reduce & eliminate the burr. Do as much of that as you can on the coarser side; if done as such, everything that follows in refinement will be much easier.

I'd also suggest using something other than bamboo for the cutting board. Bamboo has a very high silica content, which is pretty abrasive against sharp knife edges. You may be getting some dulling of the edge from that. I use a white poly cutting board in the kitchen. Even 'cheap' stainless edges hold up well, used on that stuff. Or, to put it differently, if the edge gets dull, it won't be the board doing it.

Thanks for the reply, I will take these advice and see if things improve. I think I'll still use my fine sandpapers (2000-5000) affixed to glass, since they do a pretty good job on finishing up the edge, while I'll get a decent whetstone/diamond board (so many choices out there) for establishing the first burr, which is what I struggle with the most.

 

[alexwang32]

Hi,
What does that mean?

If you sharpened scissors, each blade can slice paper or shave ...
but the scisssors no longer cut as scissors,
even though the blades are touching each other as you open/close as they should?
well that means you've ground on the wrong side of the scissors,
the inside side, ...

Uh no, I grind the inside only for removing the burr, I'm not that oblivious.

Besides sharpening them, one thing I did to all of the these scissors was that I hammers the rivet tighter in an attempt to improve their cutting ability, but this seemed to have an ill effect. Scissors that used to cut fabric now only cut paper, fabric rolls over them instead of being cut, which has disappointed a great deal. Another possibility is that I removed too much metal, and since the scissors I'm sharpening aren't of good quality I might have sharpened the good steal off, what's underneath is junk steal ( still it should pass the wet tissue test on the first few cuts right?)

 

[Obsessed with Edges]

Uh no, I grind the inside only for removing the burr, I'm not that oblivious.

Besides sharpening them, one thing I did to all of the these scissors was that I hammers the rivet tighter in an attempt to improve their cutting ability, but this seemed to have an ill effect. Scissors that used to cut fabric now only cut paper, fabric rolls over them instead of being cut, which has disappointed a great deal. Another possibility is that I removed too much metal, and since the scissors I'm sharpening aren't of good quality I might have sharpened the good steal off, what's underneath is junk steal ( still it should pass the wet tissue test on the first few cuts right?)

Scissors are real sensitive to any rounding at the cutting edge's apex. Being that their edge angle is very wide (obtuse), it needs to be very crisp to cut things like fabric or thin paper. I'd still bet the edge-rounding is the issue there; doesn't take much degradation to stop it cold, from cutting well or at all.

A quickly-cutting stone or diamond file/paddle (325 - 600 grit; like seen below) works well for crisping up the edge on scissors. In particular, if the scissors' edge isn't too far-worn, sometimes just a few passes can get them cutting well again. I like the 'paddle' type diamond hones for this, used like a file. I put the lower half of the scissors in a vise (pad the jaws) with their tip facing away and the bevel facing up. Then use the paddle in linear, uni-directional strokes from pivot end to the tip, keeping the diamond flush to the bevel. Check cutting after every 1 - 3 passes or so, and/or feeling the edge for sharpness & burrs after each pass. Then flip them over and do the other side the same way. I like to put a couple or three drops of mineral oil on the diamond hone, to keep it from getting clogged up. It'll also keep the honing smoother and easier to control, especially at coarser grit.

 

[bucketstove]

Besides sharpening them, one thing I did to all of the these scissors was that I hammers the rivet tighter in an attempt to improve their cutting ability, but this seemed to have an ill effect. Scissors that used to cut fabric now only cut paper, fabric rolls over them instead of being cut, which has disappointed a great deal.

Hi,
So are the scissor hands separating at the tip now?
Or still touching all the way?
Loose or stiff to open/close?
Only separate when you've got fabric in there??

You gotta be able to narrow it down, is it the pivot/alignment, or is it the edge sharpening

Another possibility is that I removed too much metal, and since the scissors I'm sharpening aren't of good quality I might have sharpened the good steal off, what's underneath is junk steal ( still it should pass the wet tissue test on the first few cuts right?)

Did you use a beltgrinder?

I'd say thats impossible

Do you have a $1 mini travel sewing kit?
See the little creased spear looking scissors?
Thats as close to "junk steel" as you'll get (mild steel, not junk).
Bends with finger pressure.
But, those scissor will still cuts string and paper without trouble.
Even thin plastic bag (waste basket liner).
It does struggle on thick fabric (old socks) but it will still chew through fabric.
Those are like 5 - 10 cent scissors.
I did have to tune mine for about 20 seconds (bending/sharpening)

 

[MolokaiRider]

This was all hand planed. Zero power tools. Zero sand paper.
Bubinga no less.
I swear by my Varitas jig and Shapton Pro stones
Don't fear the flattening of a water stone it is about the easiest thing I have ever done except maybe catch a cold.
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Mirror finished end grain right off the blade (I love my sharpening jigs !)
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Nice work!