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Sharpening knifes and similar tools Answered

On the weekend a friend of mine asked me if I could get his 2 fishing knifes ready for the season.
Being a nice guy I agreed as they were so blunt that you could sit on the knifes edge without even getting a scratch.

Did just the usual, you know, cleaning it first, grinding a proper angle back on it with a very coarse stone, sharpening from a 300 grit down to a 1000 grit and then of course polishing and removing the burr.
Was quite pleased with the result and decided to bring the finnished knifes back to my friend....

There are several ways to check if a knife is sharp.
Most know the newpaper cutting thing.
Some dare to try if the knife i able to shave some hair off.
And a few actually know that it is enough to check if it won't slip of your fingernail.
My friend however was used to knifes that I would consider to be piece of steel with a rounded edge...
Of course he had to try to run his finger down the blade and before I could stop him....
He said "Feels nice and smooth but I think you ruined the edge with your polishing!".
I only said "Get some bandaids before you check your finger and reconsider."
Lets just say about 10 seconds after his test he started bleeding like a pig.
He actually managed to get the cut about 5mm deep :(
We agreed that it would be best to keep these knifes in the boat and to put a note on them so he won't check their sharpness again.

There are tons of tutorials and videos showing various ways of sharpening a knife that can be used as a general reference.
But if you already know all the basic while still struggling a bit to get the edge and sharpness you desire:

The most important thing to know is what type of steel is used in your blade.
I don't mean the grade or composition, just the difference between stainless steel and old style steel that is able to rust.
You never want to sharpen a stainless steel blade with a stone that is well used on normal steel.
If in doubt clean it out!
The reason behind is that you cause the steel that is able to oxidise or rust to be worked into the stainless steel surface.
In the worst case this can cause rust spots or smalle pits in your sharpened edge.
When it comes to restoring the edge of a well worn knife some beginners and so called expert struggle to keep the angle and edge itself even and straight.
Tools to overcome this are available, like these guides for a diamond stone on a stick where you cplamp your blade in.
There are also "trolleys" that hold your blade at a fixed angle on the stone by means of small wheels.
Both have their uses but also a lot of limitations, especially when it comes to the rounded parts of a blade, like the tip or filet knife that is generally curved a bit.
Special knifes like the old Kukri knifes have a curved part that goes to the inside, these are a true pain with normal grinding and honing stones, so I will leave them out here, but feel free to ask in the comments if you need more info.
The best way I found for restoring a rounded knifes edge without special tools is by using a long diamond file.
Preferably with a quite long handle and not too wide.
Like with the guide tools the key is to cheat your way through ;)
But unlike most guide tools you will still keep the same angle in the curved parts ;)
Here are the basic tool required:
Long handled diamond file
Some wooden block or similar to get work platforms of different heights (lego blocks work too)
A long enough clamp to secure your blade on the block(s)
For the last you can also make a screw clamp like a hinge to hold the blade in place.

You want to knife to be secured so it won't move and so that you can reach all parts of the edge with the file.
Depening on what side you work on or what you prefer the file will rest with the handle either above or below the knife.
With the length of the handle you can adjust the required angle, preferably in the 20-25° region.
For the straight parts of the blade you work in overlapping sections.
Rest the handl so it aligns close to the knifes handle and move the file along the knifes edge.
It helps to use a permanent marker on the endge to visualise where you take material off and to check the work area creates a parallel area in the painted bits.
When you see some material removed move the handle of the file a bit further towards the pointy bit and continue to create the parallel boundaries.
Kepp going back and forth along the straight part of the blade until there is only a tiny area left on the edge where the marker stays visible.
For the rounded tip part you place the handle so you can follow the curve on the knife at the same angle as on the straight part.
Most knife have this area badly neglected once well used so you might end up with a slightly wider area where material is removed.
Once the edge is all reduced to the same slim marker line it is time to repaet the process on the other side at the same angle you used before.
Don't be too scared to see in a close up that your edge is not perfectly even or straight, a few imperfections will be buffed out in the next step.

To finnish the edge and smooth it out you use a flat stone or diomand plate of similar grid to the file, for example 300.
If you do this step right you won't even need fancy guides or tricks after doing it a few times.
The key from now on is keep an even angle that matches your initial angle to restore the edge.
The old masters were right here to use stones that are either secured tightly in a wooden frame or "clamped" down by a leather strap.
Apart from needing a perfectly clean and flat surface on the stone and movement will cause a more or less rounded edge again.
Every use one of these fancy chesse slicers that work like a potato peeler?
You wanna do the same with your knife on the stone.
With the stone in front of you start at the far end and move the blade down like you want to cut a thin slice of the stone.
Always with the edge towards you like cutting something off, never the other way around.
If you don't mount your stone too high you will notics that it is quite easy to use your palms as a guide to keep an even angle throughout a cutting stroke.
To find the right angle you again cheat with a marker.
But no matter what type of stne or diamond sharpener you use: use lube!!
The coarse types usually are fine with water, diomand anyway, finer or so called "oil sones" require honing oil.
Do a few strokes and check the marks you left on the marker.
Adjust until you get about the same work area cleaned as in the previous step with the file.
You will soon see that there are now uneven areas which cause a wobbly outline on the marker.
Continue with this grit until you get a nice and even outline.
For the rounded tip area you do it similar but with a slight twisting motion.
It can help to do a few dry runs on a piece of cardboard to find the right twist.
Simply place the rounded part on the cardboard at the approx angle for the sharpening.
Now move the handle so the edge follows the curve on the cardboard - the circular motion you need to get from the straight part to the tip is the "twist" you want during the sharpeing of this area.
Again, once satisfied do the same on the other side.

Now it is time to decide if you want to keep the angle all the way or if you prefer a beveled edge with a slightly wider angle for actual cutting edge.
The later is good for knifes that see a lot of abuse and hard work, the first for everything that needs to be really sharp.
I prefer sharp so lets continue with this and if you can't figure out how to get a second agnle on the edge ask me in the comments ;)
Depending on the quality of your blade you now need to work your way up the grid.
If your edge (the part with marker left) is more than half a mm wide you might want to keep going with 300 grit until no marker is left and the edge develops a slight bur on the other side.
From now on cleaning the blade and stone every few minutes is a good thing!
Rinse it off, wipe it off, flush it off, whatever works best to keep it clean.
If you go to 600 grit you will clearly see the difference in the work area.
The scratches buff out an the surface becomes smooth.
You keep doing the same slicing technique but only do as many strokes as required to get a slight bur throughout the edge on the other side.
You will feel it when you move your finger along the side, one feels smooth, one feel very rough.
Areas that stay smooth indicate that there is either still material to be removed or that you created a small dint while sharpening - the marker will tell you.
Once you get a bur with just a few strokes you know the edge is there.
Time to move the next higher grit you have available.
From here on you might need to use oil instead of water and depending on the type of stone you will need to leave some slurry on the stone - check the manual ;)
Either way the procedure is still the same: Slice a thin piece off until you get a bur.
Then do the other side until both are even.
Assuming around 1000 grid is the usual max on a hobby level and that you don't have any finer stone it is now time to take of the bur on the edge.

No matter what you try there will always be some but created when sharpening.
A lot can be prevented and smoothed out though.
To do this you reduce the pressure during the last few strokes and turn the knife around often.
When you get to the point where a single stroke causes a bur and another single stroke on the other side inverts the bur the knife is almost ready.
Polishing a knifes edge can cause a bit of bluntness.
For obvious reasons it is best to sharpen to the honing point where a 5000 - 20000grit wet stone is used, but these are quite expensive and require special care.
In other cases like our example here you need to make the best out of it:

Get some sturdy old leather like some belt.
Use proper glue and clamps to glue it onto a really flat piece of wood.
You want the smooth side glued and the rough side of the leather facing up.
Prepare the leather with some kitchen knife that is need of sharpening anyway by placing it almost flat onto the strip with the edge facing away from you.
With good pressure move the blade toward you.
You will have to do this several times to align the fibres in one direction only.
Now get some metal polishing paste or if nothing else polishing wax for metal - the fine stuff for the wax type please.
Rub it in and work in with the kitchen kifes the same as bafore, always in the same direction.
You will create a bit of a mess but that does not matter for now.
The leather will become more and more smoth on the surface until it appear quite even.
Clean the excess off and grab the real knife.
There is now enough lube and polishing material in the leather to last quite a while.
Start with the knife as flat as possible, again the edge facing away from you when you move the knife in a slicing motion towards you.
Do this for a few minutes and you will see that the sharpened edge becomes shiny where it goes into the knifes body.
Once all is polished increase the angle slightly and repeat.
In a perfect world the polishing should now go almost to the last bit of the edge, only leaving a very thin rough line.
This last line is the critical bit.
There are two ways to deal with it, pressure or time.
If you keep the last used angle but increase your pressure the blade will go deeper into the leather and the polishing should reach the front of the edge.
In the other case you slightly increase you angle but only use very little pressure, more like letting the knife rest on the leather while you move it along.
In either case you check the edge often with your finger and once it feel really smooth throuout you stop.
Turn the knife over often during this last step as even with the polishing you create a slight bur.
Only repeated turning and using as little pressure as possible will remove this last bur on both sides.

If you know think your knife is still not sharp enough than you might just have a very cheap knife... ;)

Discussions

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rickharris

3 months ago

Best advice for sharpening any tool is do little but do it often. I polish my knife on a cardboard wheel on my grinder, a little jewellers rouge give an excellent edge.

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Downunder35mrickharris

Reply 3 months ago

I like that idea!
Should have thought about a cardboard wheel ages ago for the touch ups :(
Sturdier than a polishing wheel and better to handle than a polishing stone....

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rickharrisDownunder35m

Reply 3 months ago

I have seen on good old You tube people using an MDF wheel as well, a bit more sturdy I suppose but for light work the cardbaord works fine.

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Downunder35mrickharris

Reply 3 months ago

I tried similar some years ago but was not too happy with the process or outcome.
Be it plain wood or something like MDF, you have to use dry polishing compounds and cleaning the surface out was a true pain in the behind.
So I misused the wheel for a while longer with some sandpaper glued onto it.
Worked really good for a blade I had with a hollow edge, you know like the old razor blades...

Would love to get my hands on some real sharpening and honing wheels, even if they are just 20cm in diameter.
They cost far too much though and finer grit than lets say 600 is next to impossible to get outside Japan and rural India.
When I was a kid we had an old bloke coming through town twice a year.
He offered the lond dead services of sharpening your knifes, sizzors and chisels for little money.
I watched him many times but never figured out how he got the knife so sharp so quickly.
To me it looked like he is just touching the foot operated wet wheels and the mgic happened.
He gave me one secret of his trade though:
Keep your fine slurry!
His words were that once boiled with water and dried it makes the perfect compound to put on a leather belt for honing knifes.
I only tried it a few times as I just don't enough slurry anymore thanks to diamond tools.
But the stuff acts quite weird in a good way.
Over time it makes its way deep into the leaer and the constant drying causes a very hard surface where the edge does not sink in anymore.
And of course you need a bunch of old belts as you can't use different grades of slurry on the same belt.

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rickharrisDownunder35m

Reply 3 months ago

For many years my father used a cut throat razor. (I never had the courage), He sharpened it every time on a leather strop before use. Never saw him put any abrasive on the strop though.

He was a steam engineer all his life and a tool that wasn't sharp was the devil incarnate to him. I think my Mother has kittens every time I went into the shed to help him do something.

However he taught me respect for sharp and heavy things, how to sharpen them and how to use them. Result, I became an electronics engineer!!

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Downunder35mrickharris

Reply 3 months ago

Reminds me of that guy on the talent show....
Parents spent a fortune on his medical career only so their boy becomes a magician ROFL
But it always pays off to have old school skills and knowledge :)

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Downunder35m

3 months ago

Yesterday I watched my neighbour trying to sharpen a small axe with one of these "sharpening tools" advertised on TV.
You know the stuff: Hardened steel blocks at a V-angle and you pull the blade or here the axe through.
He did not seem to be too impressed and once he started swearing and throwing the sharpener around I went for a chat.
Turned out his axe was not only blunt as but also the receiving end of some objects that you should not hit.
Imagine it looked like a kid tried to use an angle grinder to cause a serrated edge.
Offered some help by taking the rotten thing to my bench grinder, follwed by the belt sander.
Lets just say this ancient old axa was good quality and work hardened over the many years of service.
My grinding wheel got dressed nicely in the process LOL
Anyways, about an hour later I was back to my neighbour and tried to explain to him how to use his fancy sharpener the right way.
Here is the outcome:

Start close to one end of the axe edge and by giving the tool a slight angle and pull it along with LITTLE pressure.
Not like you would with a stone, more like getting butter on your toast.
After a few strokes turn the axe around so you get and even edge.
What these TV guys won't tell you is that these types of sharpening tools are really no good for a worn blade.
As it is hard steel or better something like carbide, they need a really smooth edge to work on.
Bumps, nicks and cracks like from trying to cut some wire will cause the tool to jump.
And like corrogations on the road it will get only worse.
Sure in good hands it is pssible to deal with this but there are better ways.
As a finnishing tool to keep work blades "sharp" they are not bad though.
Like said already: Do it often and do it right ;)
After about half an hour we could see the edge getting nice and shiny and despite me having used a slightly wrong angle we got to the point where the edge started to show really good.
Sadly even once I tried for a while it was impossible to cut some paper clean.
The axe was so hard that the sharpening too caused a lot of micro fractures right on the tip of the edge.
Like the burr from normal sharpening standing up.
So I went to grab my find diamond file to finnish the edge...
Personally I don't like these "easy to use" tools not very much unless they come in a sturdy frame and not as a tiny hand tool.
Too hard to use otherwise without causing a wobble along the edge.