Best way to sharpen a knife

[technophile50]

I also have found that the two times I'm most likely to cut myself are when I'm forcing a dull knife; and when I've gotten used to the feel of a dull knife, then sharpen it, and it slices smoothly and quickly through the food and into my finger. If I keep my knives sharp, it's safer.

[HowardLi]

The type of belt grinder he is using is inexpensive compared to some manual systems (including EPs, water stones, etc.) and belts cost a few dollars a piece, even for the good ones.

[Country]

As others have noted... electric motor driven abrasives can quickly ruin a knife if you're not very careful.

[dcarch]

A belt sander should only be used by someone who is very experienced. You can forever destroy a good knife in a few seconds if you don't know what your are doing. It can take away metal too quickly and the heat can de-temper the metal if you put too much pressure on the blade.

I keep a few sheets of fine grit wet/dry silicone carbide sand paper in the drawer. Put the sand paper on a flat surface and a few drops of water, you can get a very even sharpening on the edge quickly.

Of course the sheets of sand paper take no room to store and they last a long time.

dcarch

[rotuts]

for a beginner with a good quality knife this would be very good place to start:

http://www.amazon.com/Jewelstik-CN10-10-Inch-Kitchen-Sharpener/dp/B000IAZD9A

its cheaper as it has two grits. Ive been useing these for a long time and only recently went to the edge-Pro

technique is important here and in any system. but easy to master once you see that book mentioned above.

avoid electric sharpeners.

[HowardLi]

A belt sander should only be used by someone who is very experienced. You can forever destroy a good knife in a few seconds if you don't know what your are doing. It can take away metal too quickly and the heat can de-temper the metal if you put too much pressure on the blade.

I keep a few sheets of fine grit wet/dry silicone carbide sand paper in the drawer. Put the sand paper on a flat surface and a few drops of water, you can get a very even sharpening on the edge quickly.

Of course the sheets of sand paper take no room to store and they last a long time.

dcarch

It's nice that we're pointing out the disadvantages of belt sanding, but note that it takes a lot of force, applied for a fairly long time, for a steel to get hot enough for heat-treat processes to become active, seeing as there is no backing behind the belt where the knife is sharpened.

If you simply tell someone to dip the knife edge into water every few seconds, you avoid the problem completely.

As for metal removal speed... if someone tries to do this without following instructions, I wouldn't feel too bad.

Edited August 12, 2011 by HowardLi (log)

[ScoopKW]

Near the end of his career, Jackson Pollack shot paint onto a canvas using a small turbine engine. But I would not suggest that as a starting point for an art student. Learn the classic techniques first.

Same deal with sharpening knives. Buy a diamond stone or a whetstone from a hardware store -- online is cheaper if you don't mind waiting for shipping. Get a strop, too. They're cheap. Less than $100 for both -- even throwing in a ceramic honing steel. And this purchase will last a decade or more.

Learn to use the stone and strop. Learn when (and how and how often) to steel a knife. Then if you want to try belt sanders, electrolysis, angle grinders, low-rpm grinders, or whatever, you still at least know how to do it the old fashioned way.

Now excuse me while I hone on a strop for awhile.

[dcarch]

A belt sander should only be used by someone who is very experienced. You can forever destroy a good knife in a few seconds if you don't know what your are doing. It can take away metal too quickly and the heat can de-temper the metal if you put too much pressure on the blade.

I keep a few sheets of fine grit wet/dry silicone carbide sand paper in the drawer. Put the sand paper on a flat surface and a few drops of water, you can get a very even sharpening on the edge quickly.

Of course the sheets of sand paper take no room to store and they last a long time.

dcarch

It's nice that we're pointing out the disadvantages of belt sanding, but note that it takes a lot of force, applied for a fairly long time, for a steel to get hot enough for heat-treat processes to become active, seeing as there is no backing behind the belt where the knife is sharpened.

If you simply tell someone to dip the knife edge into water every few seconds, you avoid the problem completely.

As for metal removal speed... if someone tries to do this without following instructions, I wouldn't feel too bad.

Those who have used a machine to grind a knife will tell you it takes seconds to heat up the thin edge of a knife and permanently turn a $300 knife into a $10.00 knife. Dipping in water helps, but not much.

Regarding no backing behind the belt, that is a completely different issue altogether. One of the important thing with sharpening a knife is to keep the proper angle of grind for the specific knife edge. Using a belt sander with no belt backing, you will be putting a what is known as “Convex Edge” on your knife, which can be desirable if you know what you are doing and what your knife is used for, but not very good idea if you are not familiar with this topic and you knife is not designed to take on a convex edge.

It is important to know that sanding belt can only run in one direction. To replace multiple belts on the machine constantly you run into the risk of mounting the belt in the opposite direction and break the belt easily.

There is some danger if you grind your blade and not follow the direction of run of the belt. The blade can cut into the belt, and the belt can grab the knife and throw the knife at high speed in an unpredictable direction.

IMHO, do not try.

dcarch

[rotuts]

Ive used my belt sander in the past. it has variable speed and does a great job with very fine sand paper.

i dont use it any more. i never ruined a knife on it but you can in the blink of an eye. you can also damage yourself with it. but you can damager yourself in a lot of ways these days.

it one of many many methods. not the first id recommend, nor the second. but its out there and can be understood to be what it is.

I personally have been useing the Edge-Pro for about a month. once one understands that system and gets one's technique down pat, and takes ones time and Enjoys it its the equal to any system around.

might not be for you ( $$$$$ remember money? ) and its not the WEPS. but it cant be beat.

it can be matched for a lot less $$$$ with several other systems. not beat.

[wigeon]

Thank you all for your replies. After reading the pros and cons of your posts, I will go for the Edge-Pro.

[Dakki]

Those who have used a machine to grind a knife will tell you it takes seconds to heat up the thin edge of a knife and permanently turn a $300 knife into a $10.00 knife.

Basically, this. The presence or absence of backing is largely irrelevant because you are generating heat (potentially quite a bit of heat) where the steel touches the abrasive belt and most of it is concentrating in a tiny, tiny area. (Come to think of it, the lack of backing might actually be a disadvantage here, since more material would act like a heat sink). The temperature at which martensite (the stuff that makes knives hard) is destroyed varies in different alloys, but it is never very high except in hot hard tool steels. In a machine shop context we use cooling fluids directly on the contact surface when grinding.

EDIT: Good choice, wigeon. Make sure to ask if you have any more questions. Knife nuts love to talk about this stuff, as I'm sure you noticed by now.

Edited August 12, 2011 by Dakki (log)

[rotuts]

EP: excellent choice

take the time to learn how to use it properly there are vids on YouTube

pl let us know what you think

[Country]

Basically, this. The presence or absence of backing is largely irrelevant because you are generating heat (potentially quite a bit of heat) where the steel touches the abrasive belt and most of it is concentrating in a tiny, tiny area. (Come to think of it, the lack of backing might actually be a disadvantage here, since more material would act like a heat sink).

Just have to comment on this... A friend owns a slaughterhouse and wholesale/retail meat store. They sharpen their knives on an unbacked belt sander and one day I tried it. I didn't think it worked as well as I could do at home on diamond stones, but it was faster. Main thing is that the knife didn't heat that much. I never got close to changing the temper.

[Dakki]

Hard to tell without actually measuring.

[Country]

Color. I've been hardening and tempering steel since 1968.

[dcarch]

Basically, this. The presence or absence of backing is largely irrelevant because you are generating heat (potentially quite a bit of heat) where the steel touches the abrasive belt and most of it is concentrating in a tiny, tiny area. (Come to think of it, the lack of backing might actually be a disadvantage here, since more material would act like a heat sink).

Just have to comment on this... A friend owns a slaughterhouse and wholesale/retail meat store. They sharpen their knives on an unbacked belt sander and one day I tried it. I didn't think it worked as well as I could do at home on diamond stones, but it was faster. Main thing is that the knife didn't heat that much. I never got close to changing the temper.

Having said what I said, I do use my belt sander to do some sharpening, and most knife makers also use belt sanders. The point is, you have to have the skill and experience, if not you can really destroy a good knife very quickly.

dcarch

[rotuts]

did you touch the knife? i dont say this in jest either.

slaughter houses use inexpensive knives that they keep razor sharp and then after they thin out they toss them. time and sharpness is what is valuable to them. they dont use Japanese knives nor do they need to. Ive done belts. very nice but not for a beginner.

[Dakki]

Color. I've been hardening and tempering steel since 1968.

With all due respect to your experience and etc., I don't buy it. A few HRC points off aren't going to make an immediately visible difference in appearance, but they will certainly have an impact on edge stability and durability.

I've been flame hardening industrial parts (as well as machining, grinding and HVOF and plasma coating) for 12 years and dual-frequency induction hardening for one.

This is my cylindrical flame hardening rig. Roller is 52100 @ 62 HRC, 3/8" deep, 14.5" diameter. Bearing surfaces are coated in tungsten carbide.

[Country]

Okay. You guys are the experts. I'll leave it to you. But, I have been in the steel working business (my own) for nearly forty years and have been sharpening knives, and much else, longer than that.

But, you're the experts....

PS. Dakki, going by the pic, you run a pretty sloppy operation. I'd be ashamed if my shop looked like that.

Edited August 12, 2011 by Country (log)

[rotuts]

WoW a Flame War

im not an expert just trying to give reasonably sound advice to some one new. every system has its pros and its cons. its just nice to know coins always have two sides. mostly.

[Dakki]

PS. Dakki, going by the pic, you run a pretty sloppy operation. I'd be ashamed if my shop looked like that.

No hard feelings on this side.

[Edward J]

Most pro knife sharpeners do use a belt sander. It is quick, grits can be changed quicly, leather strops exchanged for belts, etc. But it takes a bit of experience to use one.

But a backing, or platten on the belt sharpener is important. If you don't have a platten, the belt does not run at a perfect 90 degree vertical line anymore when you put slight pressure on it--it bows inward, and then your bevel geometry is all wonky, or teh possibility of grindig a "hollow" along the edge is far greater.

Been in my fair share of butcher shops. Most of the guys I know are mercyless when grinding knives-- a good knife might last a few weeks before it's too narrow and has to be tossed. Most of the guys buy all kinds of knives at flea markets/garage sales and re-grind the profile to a boning knife, and then it lasts a week or two. In short, a knife is jut a tool, a hunk of steel with a sharp edge to get your work done.

[Country]

PS. Dakki, going by the pic, you run a pretty sloppy operation. I'd be ashamed if my shop looked like that.

No hard feelings on this side.

No hard feelings here either. Just had to get in a dig about your set-up.

[dcarch]

You guys can be a little edgy, but all have a sharp senses of humor.

dcarch

[HowardLi]

A belt sander should only be used by someone who is very experienced. You can forever destroy a good knife in a few seconds if you don't know what your are doing. It can take away metal too quickly and the heat can de-temper the metal if you put too much pressure on the blade.

I keep a few sheets of fine grit wet/dry silicone carbide sand paper in the drawer. Put the sand paper on a flat surface and a few drops of water, you can get a very even sharpening on the edge quickly.

Of course the sheets of sand paper take no room to store and they last a long time.

dcarch

It's nice that we're pointing out the disadvantages of belt sanding, but note that it takes a lot of force, applied for a fairly long time, for a steel to get hot enough for heat-treat processes to become active, seeing as there is no backing behind the belt where the knife is sharpened.

If you simply tell someone to dip the knife edge into water every few seconds, you avoid the problem completely.

As for metal removal speed... if someone tries to do this without following instructions, I wouldn't feel too bad.

Those who have used a machine to grind a knife will tell you it takes seconds to heat up the thin edge of a knife and permanently turn a $300 knife into a $10.00 knife. Dipping in water helps, but not much.

Regarding no backing behind the belt, that is a completely different issue altogether. One of the important thing with sharpening a knife is to keep the proper angle of grind for the specific knife edge. Using a belt sander with no belt backing, you will be putting a what is known as “Convex Edge” on your knife, which can be desirable if you know what you are doing and what your knife is used for, but not very good idea if you are not familiar with this topic and you knife is not designed to take on a convex edge.

It is important to know that sanding belt can only run in one direction. To replace multiple belts on the machine constantly you run into the risk of mounting the belt in the opposite direction and break the belt easily.

There is some danger if you grind your blade and not follow the direction of run of the belt. The blade can cut into the belt, and the belt can grab the knife and throw the knife at high speed in an unpredictable direction.

IMHO, do not try.

dcarch

It is quite easy to heat up the steel too far... if you leave the belt grinding the same spot.

Dipping into water immediately cools the steel to below 100 degrees C, and within a fairly short period of time, to near the temperature of the water. Remember, though the edge is thin and easy to heat, it is also easy to cool.

A belt grinder with a backing would simply be a quicker way to sand a knife with a stone; much of the same technique is required. No, I speak of purely sanding on a belt without a backing, to intentionally acquire a convex edge. Convex edges are, in many ways, superior to the typical hollow or double bevel grinds from the factory on most knives. Your argument about the knife needing to be made for a convex edge - I don't buy it. Without getting into the nitty gritty, a convex edge is the strongest edge.

I have never heard of a one-directional belt of this style (1"x30" meant for these small garage units). Can you link to one that is?

Why even bother mentioning that the belt needs to run away from the edge? May as well tell someone not to sharpen their knife, period, because they might cut their fingers off. Come on... somebody interested enough in moving onto the next step of sharpening is probably able to figure that part out real quick.

Anyway, don't take this as anything more than civilized discourse.