Messages

Raising a glass to Vadim!  He contributed and shared a lot for us sharpeners.  Mark Reich and now KG.  Really sad to watch our sharpening community grow smaller.

Aw, shucks Mr. Ken.  Your praise is appreciated but truly not deserved. 

I'm sure a lot of folks here don't know the history, but if anyone deserves recognition it is you for doing such a dedicated and time consuming job of taking over the Tormek Forum moderation after Jeff's departure.  6,800+ posts supporting the Tormek community.  Amazing!  I'm sure everyone here joins me in saying, thanks!

Mr. ABall-

If it helps, all the microscope images in the following post were taken with the scope I mentioned.  Lighting is everything, and I spent a lot of time getting it right.  Used diffused side lighting and it took a bit of messing around.  Shiny steel is difficult to photograph with just top lighting due to reflection.

http://bessex.com/forum/showthread.php?tid=68&pid=510#pid510

Rick-

Good to hear from you!  Nope.  I really have not been keeping up any latest Dino changes.  While beautiful microscopy is always tempting, I pretty much can get what I need from the Celestron and for as often as I use a scope I really can't justify a more expensive unit.

For everyone interested: 

Any USB scope is better than none for understanding edges and sharpening.  A stable stand is extremely important even if you have to make one.  Lighting is everything.  Experiment with side lighting.  Maybe turn off the scope top light.  Put tissue paper over a flashlight, hold it off to the side and move it around until you get the perfect image.  It takes some messing around but even the cheapest scopes can produce informative images.

I'm more than happy to answer any questions I can.  Not that I'm always right, but I'll try.

Things to look for when buying usb microscope:

1.   Magnification.  200x is about perfect.

What you want to look for is "optical" magnification, NOT "effective" magnification or "magnification dependent on monitor size". 

Optical magnification is the magnification output of the scope's lens system where it focuses on the scope's image sensor. 

Effective magnification is basically just like zooming in on an image displayed on your computer.  The more the image is zoomed in on, the grainer it gets.  You are just looking at a smaller area of the image and stretching it out to fill the monitor screen.  Very different from optical magnification.

2.   Image sensor resolution.

Higher resolution is better.  If a 20mp image from a modern digital camera is displayed on your computer screen, you can zoom in a lot before the image gets grainy.  But with a low resolution image, like a picture on newsprint, you can see the dots that comprise the image with a simple magnifying glass. 

Higher resolution scope image sensors produce images with more actual image detail.  A 5mp image sensor produces images with more than twice the image data of a 2mp image sensor in the scope.

3.   Other considerations.

With a highly magnified field, ANY movement of the scope or subject is really problematic.  The slightest bump will move the area observed and throw it out of focus.  Without a super stable stand focusing can be a frustrating, hair pulling freak show.  None of the "affordable" USB scopes have a good enough stand.  I made one from a tapping jig. 

Depth of Field:  DoF is the area of the image that is in focus.   We have all seen pictures where the subject is in focus but area in front and back of the subject is fuzzy.  This is the Depth of Field focus area.

When magnification goes much over 200X, DoF becomes EXTREMELY shallow.  At 1000x, you may need to refocus from top to bottom of a single cell.  Even with the tiny aperture of USB scope, much above 200x the DoF is very shallow.  When looking at a rolled edge for example, only the top surface of the roll will be in focus.

With super high magnification, in order to get a complete image of a rolled edge, it is necessary to focus on the top of the roll, take a picture, focus a little lower and take an image...  Then combine all the images in a process called focus stacking.  The are many software applications that can perform that task.

DO NOT get a biological scope.  They are designed for light to pass through the subject, like a blood sample on a glass slide.  All you will get with a knife blade is a silhouette. 

The best images will come from a true metallurgical scope and good focus stacking software.  Let's start at about $700.00.

Most "affordable" USB scopes have a 2mp image sensor.  Not much.  5mp is better.

About the best bang for the buck scope I've found is this one.  200x optical magnification.  5mp image sensor:
https://www.amazon.com/Celestron-Handheld-Digital-Microscope-Pro/dp/B00CMJ1I08/ref=sr_1_1?dchild=1&keywords=celestron+pro+usb&qid=1609376758&sr=8-1

All that said, even a $30.00 scope is way better than no scope and is very informative.

Hope that is helpful!

If you want to approximate Tormek honing compound it's made from 1-3 micron aluminum oxide abrasives:

Aluminum oxide  30-40% 
Petroleum distillates 15-<25%
Ammonium hydroxide 25% <1%

So basically it's 1-3 micron AO abrasive in light petroleum oil with a bit of ammonia.  I don't know for sure but I suspect the ammonia is in there for a cleaner/lubricant. 

The AO abrasives seem pretty friable and at 1-3 micron is not very aggressive stuff.  Being a very fine abrasive it puts some good shiny on the bevel.  I like it a lot and have used it for jobs other than knife sharpening.  It even removes oxidation from plastic headlight covers.

Used regularly the oil in it keeps the leather honing wheel in good condition.

Hello back Elden!  Cool to see you still here. 

Speaking from frustrating experience, if you have rust under the paint, even if the paint seems well adhered, the rust oxidation process will continue and sooner or later the paint with underlying rust will flake off.  If/when that happens you'll have the same problem again, just in a slightly different area of the frame.

To do the job right, grind the paint away down to shiny metal until there is no visible rust and then repaint.

That said, just putting a good coat of paint over it could last for years.  I guess it just depends on how much work you want to do.

I have a whole-house stand by generator.  The floor of the cabinet under the battery rusted.  I removed the majority of the rust with a wire brush on a drill and gave it a good coat of Rust-Oleum.  Three years later the rust is back.

BTW.. Hi Ken.

Maybe this is what they are talking about:
http://www.bluewondercloth.com/catalog/item/151206/9322601.htm

Mr. cbwx34 queried,  "I add bold to a part that maybe we're overlooking... what is causing your edges to so "quickly roll"?"

Hardness of the steel, cutting board impact, toughness of material being cut and bevel angle all contribute to edge dulling.  Sharper edges tend to roll more easily simply because they are thinner.  I know, a sharper edge will cut more easily and therefore less pressure is applied to the edge which causes it to dull less easily. 

The point is that there is a happy medium when steel hardness, bevel angle and how the blade is going to be used is all considered.  I know that in industrial settings they have found that for some types of blades an initial sharpness reading of 400 or more is most effective in the long run. So it varies.

Finding that perfect balance is the tricky part.

Personally, I don't have a "favorite" sharpening angle.  Like Mr. Jan states, different grades of steel can support a more acute angle than others.  A very acute bevel angle cuts easily but may not hold up.

It also depends on how the blade is going to be used.  If all a blade is going to do is gently slice through sashimi, it may perform well with a very acute bevel angle.  A blade that suffers repeated cutting board impact or is used to cut really tough stuff like cardboard all day may need a less acute bevel.

If you sharpen to 15° and have poor edge retention, try a steeper bevel.  That kind of thing.

http://tinyurl.com/yagbuarv

What I have found, and this is just my personal experience, is that a freshly sharpened very sharp polished edge will melt through tomato skin.  But very quickly the edge rolls into a smooth rounded surface that rides on tomato skin while a toothy edge, because it rolls unevenly, continues to cut. 

In a previous post I attached an image of a rolled, polished edge.  It's not hard to see how it just slides on the smooth surface of a tomato.  A toothy edge maintains its "bite" longer and is able to break the skin.  It acts like a serrated edge only on a microscopic level.

I became so frustrated with ever so slightly dull polished edges riding on various surfaces like tomatoes, plastic twine and other similar surfaces that I started experimenting with toothy edges.  The difference was literally amazing. 

I used a sharpness tester when doing the tests.  The polished edges were very sharp as were the toothy edges so it was not that the polished edges were dull to start with.  The super sharp polished edges cut everything very well.  They just didn't maintain that cutting ability.  After only a short time that frustrating riding on the surface of stuff started while the toothy edges continued to cut.  If I were to guess, that's what your customers are whining about.

That said, a chisel or a gouge needs a polished edge for push cutting.  Toothy edges are great for food slicing and polished edges a good for push cutting.  Of course there are exceptions, like sushi chefs want a polished edge, but in general, I've had much better results with toothy edges for slicing.

Like I mentioned before, your results may be different than mine.  What's cool is that you have the opportunity to do extensive real world testing which is something I don't. 

I posted this link before, but it might be worth posting it again because it's exactly what you are doing:
http://bessex.com/forum/showthread.php?tid=68&pid=614#pid614

I'll be most interested in what you find out!

Mr. sharpco,  I agree with you on one point.  If a toothy edge is what you are going for, a 4,000 grit abrasive won't get you there and honing with compound will remove tooth.  The SJ will produce a beautiful polished edge.  Great for chisels and woodworking tools, but, at least in my humble experience, a toothy edge will last longer for things like cutting tomato skin.  With almost any amount of rolling of the edge, a polished edge will ride on the skin of a tomato, while a toothy edge will continue to break the skin. 

You know, play with it yourself.  Grind a toothy edge and carefully deburr so as not to remove the "toothy".  Grind a smooth edge and then compare how each cuts a tomato after chopping up some potatoes.  You may well arrive at a totally different conclusion that I suggest.  Nothing wrong with that!

I think the most important thing is to actually take the time to run the experiments yourself, and form your own conclusions based on your own findings.  If you don't do that, you are at the mercy of the opinions of others, and in the knife sharpening world that can be very confusing!

A microscope can be very informative.  If a blade just rides on the skin of a tomato, you can actually check out the edge and see why.  It won't answer all questions, but it's not a bad tool to have in your tool box. 

Your customers are providing you with valuable feedback.  You have a unique advantage insofar as your customers are running tests for you!  How cool is that?  Experiment with different edge finishes, bevel angles and the like and see what works.  That would be some real world, empirical data that most folks don't have access to.  Personally, I'd love to hear what you discover! 

The problem with polished edges is that they roll into one even, round dull roll of steel at the edge.  From my experience this happens quickly.

I prefer a 150 grit finished edge, debured without compound.  Remove the burr but don't remove the tooth.  As you have noted, compound is an abrasive and will smooth out the "toothy" edge.  IMHO, smooth edges are good for shaving and push cutting.  For slicing and general useful edge retention a toothy edge is the way to go.

You might enjoy this entire post, but here is a comment from a guy who sharpens/rents knives into restaurants:

http://bessex.com/forum/showthread.php?tid=68&pid=614#pid614

As mentioned in the previous posts, what causes a blade to dull is rolling of the edge.  Sometimes it's bad enough to actually feel with a fingernail.  I know, you could whack the edge on something hard and actually bash it in, but that's not what I'm talking about. 

I took a knife and put a highly polished, mirror bevel edge on it.  It was very sharp, measuring 120, 130 and 125 gf with the PT50B sharpness tester.  It melted through tomato skin effortlessly.  Then I cut a bunch or cardboard with the knife.  No impact, just slicing cardboard.

See first attachment.

After cutting the cardboard, sharpness readings were 270, 240, 315.  Much less sharp.  The blade just slid back and forth, riding on the surface of tomato skin.   The thin, very sharp edge had rolled, forming a dull rounded tube on the edge. 

See second attachment.

So after the edge has rolled, there are two things that can be done.  One is to simply straighten, or un-bend the rolled edge by dragging it over a hard smooth surface.  The other is to apply an abrasive to the edge such as a ceramic rod or other abrasive material.  That would probably straighten the edge as well as abrading some of the steel away.  Sort of micro-sharpening.

Obviously softer steel will roll more easily than harder steel.  But harder steel is more difficult to sharpen and can be prone to chipping.  Harder steel is more difficult to straighten when the edge is rolled, and will tend to fracture more quickly than softer more malleable steel after repeated un-bending of a rolled edge.

I guess it depends on how the knife is going to be used in order to find that perfect blade for a particular task. 

Mr. Sharpco,

Great question!

What are the factors in edge retention?

Hardness of the steel of the blade.
Brittleness of the steel.
Type of edge finish, toothy or polished.
Bevel angle.
Material the blade is cutting.
The amount of impact the edge suffers during use.
Initial sharpness.  A sharper edge is thinner.
Incomplete burr removal.

Consider what an abrasive does.  The abrasive removes steel to sharpen, (make thin) the edge.  Abrasive can be coarse or fine which will affect edge finish and how quickly steel is removed.  That's all an abrasive does.  Abrasives do not, and cannot, impart any magic quality, extra hardness or edge retention to the edge. 

IMHO, other than the above mentioned considerations, whether the abrasive is a Tormek wheel, an abrasive belt, a wet or dry stone or whatever, the type or brand of abrasive has nothing to do with edge retention. 

For whatever reason, (actually marketing), knife sharpening has been made way more mysterious than it actually is, and has created a marketplace that promotes over-thinking what is actually happening.  I see it all the time.  This stone is better than that stone.  You must use our brand of special sauce when honing.  Antelope butt leather is the only way to go for the "keenest" edge.  You can only get a "scary sharp" edge with paper wheels and diamond paste and on and on.  It makes something very simple seem almost impossible to understand when it does not need to be at all.  The marketing turns simplicity into a confusing, frustrating, hair pulling freak show that only some sort of Zen monk can understand and then only after years of tortuous study with copious blood and treasure spent. 

Please understand that I am by no means and expert, and really don't mean to come off as some sort of know-it-all... Really!  There is no perfect way to sharpen a knife, and everyone will develop their own methods of doing so.  That's the fun thing about sharpening; the learning and experimenting never ends. 

Anyway, I hope you find something useful in my diatribe.