Getting started

[grepper]

I still am struggling to know how many honing passes I need on the stropping wheel. 

So, how many passes on the honing wheel is required?  Exactly three.  Or ten.  Or seven.  That is a difficult question to answer because the real answer is that you need to hone until the burr is removed and/or you have achieved the desired polishing of the bevel you wish.

The amount of metal in and the type of burr formed depends mostly on two factors; the coarseness of the grindstone and the hardness of the steel.  A coarse grind will tear at the cutting edge producing a thicker, chunkier burr. A smooth grindstone removes less metal more evenly and produces a thinner, more even burr.  Of course the angle of grinding will also play a part.

Harder steel tends to be more brittle and chip easily.  When sharpening, it tends to produce smaller, irregular burrs because the brittle steel simply breaks off rather then bending over the edge.

Softer steel, being more malleable, tends to produce more burr because it simply bends at the edge and stays intact.  Observe the image at the end of this post.  Here the burr has actually formed a roll of steel bent away from the edge.  It is a classic "wire edge" burr.  Shaving would be very uncomfortable with that blade!

Oddly, hard and soft steel is somewhat similar to a bar of chocolate.  If you take a potato peeler to the edge of a hard, cold bar of chocolate, the chocolate just crumbles into pieces. 



But let the chocolate warm and soften some and it forms decorative chocolate curls you can use to embellish tasty culinary delights. 



So, how much honing is required?  Well, consider the below image of a burr.  If you press the side of the blade opposite the roll burr against the honing wheel probably not much will happen because the burr will not impact the wheel.  But flip the blade over and the bulging burr will be bent in the opposite direction over the cutting edge.  After a few iterations the metal will fatigue and the burr will start to break away.  However because the steel is softer and more malleable, it may take a more bending back and forth than would a harder more brittle steel.

But... check out some of the images in the previous post where the burr sticks straight out from the edge and imagine what happens when those blades are pressed against the honing wheel.  Because the burr extends straight off the edge, very little bending occurs because the burr only slightly impacts the leather.  However, the leather is soft compared to the blade and depresses slightly when the blade is pressed against it causing some wrapping of the leather around the cutting edge.

That is why it can be useful to wipe the blade over a piece of towel or soft wood to tear away and/or deform the burr to increase contact with the honing wheel.    If you have a blade that is not getting sharp even after some honing and you suspect a burr is the issue, try it.  It actually works!  The results can be surprising and dramatic.

Hopefully that helps in answering your question as to how many passes on the honing wheel are required.  Exactly three.  Or ten.  Or seven.

[Jan]

Another very nice and well documented burr removal consideration, Grepper, thanks. Much appreciated!   

Jan

[grepper]

Thanks, Jan.  Any time!  Its cool how once you get a good look at a burr and give it a little thought, it all becomes clear what's happening.  But then, I guess that's true of a lot of things.

[Jan]

Wise words, I fully agree with you! 

Jan

[Herman Trivilino]

Mark, that second image reminds me of a saw blade! That knife will slice tomatoes nicely.

Slicing through paper and shaving arm hair are nice parts of a demonstration designed to impress potential customers, but they don't necessarily tell you how well a knife will perform. A very sharp knife that will shave arm hair might last only a few sessions in the kitchen as the edge may easily break off. How long an edge lasts is sometimes more important than its first performance.

[Herman Trivilino]

That is why it can be useful to wipe the blade over a piece of towel or soft wood to tear away and/or deform the burr to increase contact with the honing wheel.

Ahhh... So my technique of wiping the blade to check for burrs may actually aid in the removal of the burr. Good to know. 

[grepper]

Slicing through paper and shaving arm hair are nice parts of a demonstration designed to impress potential customers, but they don't necessarily tell you how well a knife will perform. A very sharp knife that will shave arm hair might last only a few sessions in the kitchen as the edge may easily break off. How long an edge lasts is sometimes more important than its first performance.

Herman,

I gotta agree with that!  For general kitchen use, a highly polished super smooth edge that works well for shaving and push cutting paper just won't last very long at all.  It's not that difficult to produce a polished, perfectly smooth edge that you can shave with and will slice tomato, broccoli and onion skin and not ride on the surface, but it has to be really super sharp and an edge that sharp and thin just doesn't hold up at all.  A few contacts with the cutting board and almost immediately there is a noticeable decrease in sharpness and it starts riding on tomato skin.  From personal experience, it does a great job of slicing through human skin though!  It slices finger meat so cleanly the first thing you notice is epidermal leakage, and it doesn't hurt until the source of the leakage is discovered and observed.

Of course there is a big difference between a more saw like edge created by sharpening with a coarse grit and a rough edge caused by piles of burr smushed down on the edge.  The former is sharp like a saw, while the latter is just plain rough like a wire covered with abrasive compound that abrades it way through stuff.

Ahhh... So my technique of wiping the blade to check for burrs may actually aid in the removal of the burr. Good to know. 

I know you have a 40X microscope and I would be interested in your observations.  Get a good burr going and carefully examine it under the scope.  Then give it a few good wipes on the old towel and examine the burr again.  What do you see?  Then drag the blade down the edge (with the grain) of a piece of pine board and examine the burr under the scope again.  How does that compare with the old towel wipe?

Here is a progression of sharpening and honing from a very coarse grind burr covered mess to a polished, super sharp most excellent finger meat slicer.  The first one, after burr removal, would be an excellent tomato skin slicer!

Kind of interesting to see how it progresses.  As the blade is sharpened with finer and finer abrasives, the grooving on the bevel is smoothed away, ending with the final, highly polished with Tormek compound, finger meat slicing, mirror bevel finish.

The blue marker on the bevel was so that I could photograph the same area of the blade.

[Jan]

Grepper, inspired by your nice microscopic images of knife edges I began to look at home for some microscope. I have found an ancient pocket microscope shown below. Do you think it may be good for burr observation? I have to clean the lenses and add some LED illumination, an opening for it is there ready. 

On the housing there is a figure 278. I am wondering if it describes the magnification or the serial number. 

Jan

[grepper]

That's an antique all right!

I have no idea about those numbers either and I'm no expert on microscopes.  While it does look like there is enough room for 278X worth of lenses, 278X would be an odd magnification level.  You know, generally you see stuff like 40X, 100X, 150X, etc.

I did a quick search and found nothing other than a bunch of antique scopes on Ebay.  If you dissemble it, there might be some markings on the lens rings that would enable you to figure it out, but who knows.  It might have a very small field maybe only a few planeria wide, but really I'm just babbling. 

Have at it!  Just stick a ruler under it and, dirty lenses and all, and see what you see!!!  That should quickly tell you if it's worth pursuing. 

Any amount of magnification is better than none.  Herman has a 40X scope.  He may have some comments on how good that is for checking out blades.

http://www.freshairphotography.co.uk/services/photomicrography/#prettyPhoto[gallery]/0/

I'm using a 200X, 5 mp USB scope.  It don't think the images I posted are 200X but somewhere between 50x and 200X.  With the cheap USB scopes, the mag level changes when the lens to subject distance varies and they can focus at different distances, so there is no way to really know the mag level.

You can pick up a USB scope for $25-$35 to play with.  Some go to 800X, but really 200X is about the max for checking out blades.  Any more mag than that and the depth of field becomes so shallow that the top side of a pin is in focus but the bottom is not.  Very difficult to work with.

The cheap USB scopes are futsy to use.  Difficult to focus because the slightest bump throws them out of focus and you have to touch them to focus.  Move the blade and it's out of focus again.  Lighting reflective surfaces is problematic too.
The biggest problem is holding the scope and blade perfectly still.  I even thought of mounting the scope on my milling machine to use as a rock solid adjustable stand, but the mill and computer are in different rooms.

Nonetheless it's a lot of fun to play with and pretty interesting! 

Let us know what you see with you new toy!

[Jan]

Grepper, thanks for your thoughts and recommendations.    You are correct, it is rather a toy than a tool for checking blades. The aperture is very small. The figure 278 is probably a serial number and not magnification. The major disadvantage is that the microscopic images cannot be stored and shared. 

Jan

[grepper]

If you want to store and share your images then you have two options.  USB scopes, $20 to a $A LOT, or camera attachments for regular optical scopes, $A LOT to $A WHOLE LOT More.

My advice would be to get a $20 - $50 USB scope just to check it out and have some fun.  As you can see they actually work and are useful.  Right off you will see what I mean about the focusing issue.  It's totally doable, just futsy.  Purchasing or making a rock solid, adjustable stand would go a long way.  I've just cursed the issue every time I use the thing, but put up with it nonetheless.

The more optical megapixels the better.  Ignore interpolated or digital magnification- you can just use Photoshop to zoom later-same thing.   Get at LEAST a 2mp model - 5mp is better.  Get USB 3.0 if you can, but last I looked those were few and far between and you pay a super premium.  USB 2.0 is so slow that when you move the subject there is a huge and jerky delay on the computer screen.  That pretty much rules it out as a live field tool (something I really wanted) for doing micro-soldering for example, let alone doing anything like injecting cells with DNA strands to GM a tomato cultivar to have soft skin so you don't need such sharp knives to cut it.

Get one!  They are inexpensive, informative and fun.  Then post some pics and show why some knife you have just won't get sharp and how if you had gotten a USB scope sooner you would not have ground the knife down to a toothpick trying to get it sharp because you would have understood what was happening down there on the edge!

[Jan]

Thanks again for your valuable advice. 

Jan

[Herman Trivilino]

Kind of interesting to see how it progresses.  As the blade is sharpened with finer and finer abrasives, the grooving on the bevel is smoothed away, ending with the final, highly polished with Tormek compound, finger meat slicing, mirror bevel finish.

What were the abrasives used in the progression? I'm no expert but my experience with sanding wood indicates to me that somewhere along the way, likely in the step immediately after using the Tormek grindstone prepared in the fine state, there was too large of a step in abrasives or grit size. The reason I say this is in the final image you can see that the deepest grooves left behind by a more abrasive grit were not removed by later less abrasive grits. The spaces between the grooves are polished to a mirror finish, indicating that the finest of grits did their job well.

I have seen the same thing after applying a finish to a piece of wood. Sand, for example, with 80 grit sand paper followed immediately by 220 grit and you'll see a smooth surface in between deep groves left behind by the 80 grit abrasive. You will need to apply a finish to see this, even if it's only some mineral spirits applied with a rag.

[Herman Trivilino]

That's a nice looking scope, Jan. My guess is that the narrow field of view might be a disappointment. If you look at a ruler with both eyes, one naked and the other scoped, you can with a little practice see both magnified and unmagnified images of the gradations on the ruler. From this you can estimate the magnification.

My scope is a dissecting microscope. It's binocular with a wide field of view and a 40X magnification. It gives me images much like the ones Mark (grepper) posted so I would estimate that the magnification in those images is somewhere around the range 60X to 100X. You want to be able to see a good-sized section of the entire bevel, and 40X seems about right.

I've seen images of knife edges with higher levels of magnification, made with an electron microscope, and they were used to examine the actual edge itself to determine the effectiveness of different sharpening strategies. But here we are interested instead in the polishing of the bevel and burr removal, so less magnification is more desirable.

[Jan]

Grepper and Herman,

I am exhorting my wife to buy for me a school microscope as a Christmas present which makes my budget less tense. Because my shop is in the basement and my computer two floors above I have decided to buy an off line working microscope with LCD display which can store the images on SD memory card. I have now to be a good boy to ensure that my Christmas wish will be fulfilled. 

I hope it may be good also for grandchildren. I wondering if it would be good to buy also a basic set of prepared slides for use in biological education. 

Jan