The picture is of linear ball bearings. Sometimes they are called "circulating ball bearings" because the balls roll around in a closed loop. You can find them in many places, including McMaster.com.

For example:
www.mcmaster.com/#linear-bearings/=lrc0y9

Machinist and author Tom Lipton wrote that one should read through the entire McMaster catalog. "Yes, read it," he said. I certainly have learned a lot from just browsing through it. If you are a mechanical designer or hobbyist-maker, I very much recommend browsing McMaster's catalog, as well as other catalogs.

btw, if you care, Tom Lipton's book is here:
www.amazon.com/Metalworking-Sink-Swim-Ma...s+%22Sink+or+Swim%22

Keep in mind there are a zillion different types of bearings for a zillion different applications and they have different levels of precision and robustness etc.

Sincerely,
--Lagrangian

P.S. McMaster.com doesn't always have the best prices, but their catalog is huge and full of information. So it's good to browse, but probably worth comparison shopping once you know which specific part you want.

I don't know much, but the chart on this web-page might be useful:

Bechem Lubrication Technology GMBH
"Compatibility of lubricants with elastomers and plastics"
www.kutzendoerfer.at/files/compatibility...plastics-english.pdf
bechem.com/uploads/produkte/en_lubricant...stomers_plastics.pdf

If you want to try a pure 100% mixure of Teflon and fluorinated oils (PTFE, PFPE, etc.), then you could try Extreme Fluoro Grease. But I don't know if it would attract dirt/grime/swarf because Extreme Fluoro Grease is not a dry lubricant.
www.amazon.com/Finish-Line-Extreme-Fluor...xtreme+fluoro+grease

However, based on the chart above, it seems Teflon and Teflon-like lubricants have the broadest compatibility with plastics. This makes sense to me, because Teflon is chemically very inert. So inert, it is often used as the lining of pumps used to move acids and other caustic liquids.

That said, I know very little about lubrication and plastics/polymers. Hopefully some engineer can chime in, or someone can find a lubricant which is designated as compatible with nylon.

Sincerely,
--Lagrangian

I'd love to help with the wiki. A bit busy, but I'll find some time!
If nothing else, I would like to help with the list of "Sharpening Length Scales."

Sincerely,
--Lagrangian

I've been using the Wixey Digital Angle Gauge, which is very similar to the iGaging Angle Cube. On paper, the Wixey is supposed to have an overall accuracy of 0.1 degrees, and a repeatability of 0.1 degrees. It has a resolution of 0.1 degrees.
www.wixey.com/anglegauge/index.html#wr300

I have a small granite surface plate, and a sine bar, so I may try to test its accuracy.

There are very high accuracy digital inclinometers, but they are expensive. The one below only measures a limited range of +/- 20 degrees, but has very high accuracy (0.003 degrees).
www.digipas.com/DWL-3500.php

Alternatively, you might be able to rig something up with a machinist's spirit level (also called an engineer's level) which is basically a very precise bubble-level with liquid. You would need something like a sine bar, gauge blocks, or angle gauge-blocks, and/or a micrometer. You can buy non-digital engineer inclinometers which are already rigged up this way, but they're very expensive (several hundreds of dollars). Of course, at this point, you're probably insane. Have I thought about this? Yes. I got quite curious about general metrology, and have been reading up on it and looking at company websites that sell metrology products.

In terms of cutting performance, I probably wouldn't notice a +/-1 degree difference.

Sincerely,
--Lagrangian

Hi Everyone,

I thought it might be worth excerpting part of Prof. John Verhoeven's work on stropping. This is from his technical report,_Experiments on Knife Sharpening_ which is free to download here:
www-archive.mse.iastate.edu/fileadmin/ww...even/KnifeShExps.pdf

Verhoeven had a hypothesis about stropping, which he then tested experimentally, and we can compare notes to Clay's microscope images.

On page 19, Verhoeven states his hypothesis:

"It was the opinion of the author at the start of these experiments that clean leather strops would contain sufficient levels of natural abrasives adequate to produce significant improvements in the edge quality. Therefore experiments were done initially on clean leather strops. This was followed by experiments done on leather strops coated with a thin layer of honing compound."

To test this hypothesis, he used a scanning electron microscope (SEM) to image the knife edge. Verhoeven's images come in triples:
(1) The first image is straight into the edge of the knife. That is to say, figuratively, the knife edge would cut your eye. SEM's have insanely huge depth of focus, so despite this view, the entire field of view is in focus! This view allows you to see both bevels and the apex itself.
(2) A side view of the "top" bevel.
(3) A side view of the "bottom" bevel.

So was Verhoeven's hypothesis correct?

Here are the results before and after stropping:

-----------------------------------------------------------------
Before:


-----------------------------------------------------------------
After:


-----------------------------------------------------------------

Verhoeven's concludes his hypothesis was wrong:

"The stropping action on the clean leather does not appear to have had much effect on the condition of the as-ground edge. The bur shown in the edge views may be just a bit smaller, but it is only a minor effect. The abrasive grooves along the faces appear to be little affected by the action of the stropping. This result is typical of what was found on additional experiments using the second clean leather strop described above. Experiments with clean leather stropping of blades prepared on 600 grit wheels showed that the clean strop was not effective in removing the larger burs formed on the 600 grit wheels."

Compare this to stropping with compound.

-----------------------------------------------------------------
Before:


-----------------------------------------------------------------
After:


-----------------------------------------------------------------

Verhoeven concludes:

"The chrome oxide abrasive used on the blade of Fig. 26 has produced a dramatic reduction in the size of the remnant abrasive grooves on the face of the blade. As shown in the edge view of Fig. 26 the bur width is on the order of 0.4 to 0.5 microns."

-----------------------------------------------------------------

So far, if you look at Clay's results, they seem to me, to be similar to Verhoeven's. To my eye, Clay's results with plain leather, or plain leather plus alcohol, show minor changes. But when compound is used, the effect is easily visible. It will be interesting to see Clay's results after he gets the plain paste.

One must keep in mind this is not an apples-to-apples comparison, because we don't know the differences between Clay's stropping procedure and Verhoeven's. Even so, the similarity between Clay's and Verhoeven's results is reassuring to me.

Sincerely,
--Lagrangian

P.S. Clay, your images are great, and thanks for all the experimenting!

Hi Clay,

I'm no expert on leather, but here is what I've heard here and there on various forums:

(1) Some leathers contain silicate particles (basically glass). Some speculate that the silicates are abrasive enough for stropping with plain leather.

(2) Leathers can be tanned in different ways. There is vegetable tanning, and then there are chromium and other tanning methods. I have no idea if these affect the abrasiveness of the leather, if at all. I think vegetable tanning is recommended for strops and sheaths because the chemicals used are not corrosive for metal, but the other tanning methods have chemicals that could cause corrosion or patina.

I don't have any definitive references for either of these. So just take them as hear-say!

Sincerely,
--Lagrangian

Hi Clay,

It'll be awesome if you get to collaborate with an SEM lab at Sandia National Labs! Right now, I don't have solid ideas about what experiments to do for an SEM, but if I think of anything, I'll be sure to let you know.

Here are three half-baked ideas:

(1) General strategy: Using your metallographic microscope, come up with some theories about what is happening, and also what your microscope cannot see (because of optical limitations). Then use SEM to test theories, and see what you couldn't see.

(2) A common technique when sharpening with stones is to use strokes that are 45 degrees from the knife edge. There are two directions for this, which are 90 degrees apart. So you can use one direction for a grit, and then when you go to the next finer grit, you can sharpen in a direction 90 degrees from the previous scratches. That way you can more easily see when you've removed all the scratches of the previous grit. I think you've mentioned this a few times.

Are we applying this to stropping? Sharpen with a stone in one direction, then strop in a direction perpendicular to the scratches from the stone. If there is burnishing, this might make it easier to see? Perhaps you are doing this already?

(3) How about traditional burnishing? Sharpen a knife with a stone, then burnish it with a hard smooth piece of metal. This could be a knife steeling-rod, a burnishing tool, or maybe even a ball bearing? Then examine it under the microscope (before and after). Not sure what this would tell us, as it is likely to be a very different kind of burnishing. But maybe it would be interesting and informative anyways?

Hi Philip,

What do you think would be a good experiment to test if burnishing is happening during stropping? Even if we couldn't perform the experiment, maybe people at Sandia could?

Sincerely,
--Lagrangian

P.S. Clay mentioned Sandia here:
www.wickededgeusa.com/index.php?option=c...8&Itemid=63#6643

Hi Philip,

Good point about the different size of contact-areas between a sharpening rod and a flat stone.

As you mention, Yuzuha's image do not have a length scale, and do not show the surface finish before applying the Spyderco stones. So this makes it a bit trickier to interpret.

As for Yuzuha's opinions, I think she's not very active in the forums anymore, which is too bad.
In a post, Yuzuha says,
"Afraid I have had some health problems and wound up retired before my time, so I have not been doing much with knives or stones for the last couple of years but I still drop in KF and foodie forums once every few months to make sure the old crew is still having fun with such questions as 'What exactly is a grit size, and how do you measure it even if the particles are not uniformly shaped,' and other assorted mysteries of the universe."
www.bladeforums.com/forums/showthread.ph...0887066#post10887066

Sincerely,
--Lagrangian

Hi everyone,

Mark76 contacted me about microscope images of burnishing that is caused by sharpening with Spyderco's ceramic stones. He thought we might be intersted in them.

The following are images from Yuzuha of www.FoodieForums.com. Sadly, Yuzuha's original post has broken image links due to a change in ISP policies. I was able to contact Yuzuha herself, and she gladly sent me the original images. I then reconstructed her entire post on www.bladeforums.com. Since it may be relevant to our discussion here, I'm posting the reconstruction here as well.

Reconstruction of Yuzuha's post:
www.bladeforums.com/forums/showthread.ph...0887400#post10887400

Yuzuha seems very friendly and happy that we're interested in her post:
www.bladeforums.com/forums/showthread.ph...0887066#post10887066


----------------------------------------------------------
05-23-2012, 09:40 AM #78 Lagrangian

Hi yuzuha, Everyone,

yuzuha, thanks for your reply! It is great to hear from you, and wonderful to have your photos recovered.

I'm not sure what the best way is, to make sure the photos never disappear. It seems that bladeforums.com does not allow one to attach an image or file directly to one's post. So for now I'll try using imgur.com.

Below is a reconstruction of yuzuha's original post to www.foodieforums.com with the microscope images that she e-mailed me. Below that is her e-mail that includes the photos, plus some notes.

-------------------------------------------------------------------------
-------------------------------------------------------------------------
Original Source:
www.foodieforums.com/vbulletin/showthrea...mp;p=23422#post23422

-------------------------------------------------------------------------
Thread Topic: sharpening - where to start w/ a new knife?
Post Date: 12-13-2006, 09:22 PM

yuzuha
Super Foodie


Join Date: Mar 2005
Location: Nebraska
Posts: 416
-------------------------------------------------------------------------

To start, I doubt the knife's angles are the same as the sharpmaker's (that 40-30 stuff seems more appropriate for outdoor knives and the like anyway), so you probably are just scraping the side of the bevel somewhere with it. Are you sure it has the same angles on both sides? Some double sided Japanese knives come with 70/30 or some other ratio bevels, and you can't do those on a Sharpmaker anyway (I only use my Sharpmaker on my Wushof's and Hecknel's... the 30 degree setting sharpens those up nicely, though I think they come with something closer to 22-25 degrees).

Generally, what I do is grab a 2k or 5k waterstone (depending on how sharp it seems in the first place) and sharpen it up a bit using the existing angles (you can rock the bevel on the stone, or sometimes go by visual clues in the water, to tell when the bevel is flat on the stone and just use whatever angle that is without caring what it is). If the edge seems too fragile, then I may drop back to the 1k and raise the spine just a smidgen and give it a slightly thicker bevel, but mostly I haven't had to do that.

Grouch, I have a table of waterstone grits (Shapton, old JIS standard and current JIS standard, Norton and DMT members.cox.net/~yuzuha/jisgrit1.html but bond makes a difference too since, while Norton says their 8k actually uses abrasive of a size equivalent to Shapton's 4k, everyone says it actually leaves a finish somewhere between the Shapton 5k and 8k), but it doesn't have sharpmaker rods in it... think that was CBWX34's spreadsheet.

Here is a photomicrograph of the Sharpmaker ultra-fine (comes with the medium and fine rods so I ordered a set of the ultra-fine too)

[Broken image link: http://members.cox.net/pihughes/superf25.jpg]


(25x objective, about 1,400x total). There are some larger and quite a few smaller (plus the tips of larger grains poking out of the matrix), but the majority of the larger grains appear to be around 2,000 grit JIS. But they are rounded and held tightly in a very dense matrix so they do not cut at all like a waterstone. Instead, they burnish like an orange stick on modelling clay, and, also like smoothing clay with a stick, the rods seem pull loose little balls of metal and smear them over the surface and leaves a finish that looks like this:

[Broken image link: http://members.cox.net/pihughes/surspyuf.jpg]


Leaves the burnished part nice and bright the surface isn't exactly smooth. Here is the same hunk of metal that I polished on a Naniwa 10k at a right angle to the sharpmaker that exposes the gouges made by the balls of metal the sharpmaker pulled up:

[Broken image link: http://members.cox.net/pihughes/surnansc.jpg]


Anyway, while the UF rods are probably 2k-3k grit abrasive, they do seem to leave a 5k-8k finish in the smooth burnished parts (the gouging/streaking makes them unsuitable for polishing the sides of blades but that should be less of a problem on a thin edge bevel).



Pam
--------
Sue ikki
mi hatenu yume no
hotsure kana---Choko
(This final scene, I
I will not see to the end.
My dream is fraying.)

-------------------------------------------------------------------------
-------------------------------------------------------------------------
E-mail from yuzuha to Lagrangian with recovered photos:
-------------------------------------------------------------------------
From: yuzuha
To: Lagrangian
Date: 2012/05/23
Subject: spyderco stone pics

Hi got your e-mail. I left a note on bladeforums (OMG I actually remembered my password for 6 years! Now if I could just remember why I went into the other room!) My ISP trashed my web space including my web site, and the pics I was hosting on it, but I did find some of the pictures on my old PC.

Superf25 is the spyderco super/ultra fine rod at, I’m guessing about 1,400x

Surspyuf is the .25" x 1.5" surface of a .25 x .5 x 1.5 inch block of stainless steel that I polished on the rod

Surnansc is the same surface polished on a 10k Naniawa super stone (not the chosera) at a right angle to the spiderco to show the gouges left when the steel galled under the spiderco.

A knife bevel is smaller and the steel is a trifle harder, and carbon steel is not as gummy so I doubt you’d see tear-outs like that unless you were actually trying to polish the side of the knife rather than just sharpening it. Even then it is microscopic. The side of the block was a hazy mirror finish after the spiderco and a bright mirror finish after the naniwa but the gouges were not noticeable to the naked eye.

Glad to see there are even more crazy people in the world that think about this stuff J

Now I am going to have to read all those links in that thread you guys created. Anyway... hope the pics help.
Later,
Pam


[ Images attached to this e-mail are now at imgur.com in the album:
imgur.com/a/KVdMk#0 ]

-------------------------------------------------------------------------
-------------------------------------------------------------------------

Sincerely,
--Lagrangian
------------------------------------------------------------
"What grit sharpens the mind?"--Zen Sharpening Koan

Wow, what a fascinating thread, I've only caught up reading recently.

Clay, those pictures are awesome!

I don't have too much to add to the speculation, but I have some information that might be relevant.

------------------------------------------------------------
(1) Abrasion is a very complicated subject. There are entire engineering books about just abrasion, and then separate entire engineering books about polishing and lapping. When abrasion is not desirable, it's called lubrication. And lubrication has entire books written about it. Not to mention, friction is poorly understood, even today, despite centuries of scientific study. My thought is to speculate, make theories, and do tests, but then to keep in mind that such things can be insanely complicated which means we could easily be wrong.

btw, I hope to eventually read two engineering books, one on abrasion, and another on polishing and lapping.

------------------------------------------------------------
(2) In Prof. John Verhoeven's technical report, _Experiments in Knife Sharpening_, he has several scanning electron microscope (SEM) images of knive edges before and after stropping. He also tried stropping with and without compound. Verhoven's pictures are the highest resolution and most detailed images of knife edges I have seen so far. It may be worth reviewing his work, and comparing notes with Clay's studies.
www-archive.mse.iastate.edu/fileadmin/ww...even/KnifeShExps.pdf

------------------------------------------------------------
(3) Just a reminder of length scales relevant to knife sharpeners:

The two most important length scales are:
0.4 microns, which is the sharpness of a modern razor
0.2 microns, which is the resolution limit of optical microscopes. btw, this resolution limit is from physics of light, which diffracts slightly as it goes through the microscope objective. That slight diffraction causes blurring. Only very high-quality optical microscopes can approach this resolution limit. I would not expect any "consumer" microscope to achieve a resolution of 0.2 microns, but a high-quality laboratory microscope probably can get close.

180 - 7 Microns: Diameter of human hair. en.wikipedia.org/wiki/Hair
100 Microns: Approximate thickness of paper (copier paper of weight 24 lbs; 500 sheets is about 2 inches thick).
16 Microns: Thickness of household aluminum foil. en.wikipedia.org/wiki/Aluminum_foil
25.4 Microns: = 0.001 inches (1.0 mil). Standard resolution for an imperial caliper.
2.54 Microns: = 0.0001 inches (0.1 mil). Standard resolution for an imperial micrometer.
0.75 - 0.38 Microns: Wavelength of visible light. en.wikipedia.org/wiki/Visible_light
0.4 Microns: Sharpness of a modern razor blade. www-archive.mse.iastate.edu/fileadmin/ww...even/KnifeShExps.pdf
0.2 Microns: Resolution limit of optical microscopes. www.microscopyu.com/articles/optics/objectiveproperties.html
0.05 Microns: Sharpness of diamond coated razor blades. www.technologyreview.com/computing/25988/
0.005 Microns: Sharpness of a diamond microtome knife. www.tedpella.com/diamond_html/diamondk.htm
0.003 Microns: Sharpness of concoidally fractured obsidian. en.wikipedia.org/wiki/Obsidian
0.003 microns: Distance between a hard drive head and the spinning platter. en.wikipedia.org/wiki/Disk_read-and-write_head
0.00034 Microns: Van Der Waals diameter of a single carbon atom. en.wikipedia.org/wiki/Van_Der_Waals_Radius

The needles used in scanning-tunnelling-electron-microscopes (STEM) and atomic-force-microscopes (AFM) are so sharp they literally have a single atom at their tips.
Also, x-ray telescope mirrors are atomically smooth. www.mpe.mpg.de/xray/wave/technologies/mirror.php

This is also fairly interesting when combined with Komitadjie's Grand Unified Grit Chart, which is an approximate conversion between sharpening stone grits and microns. The graph below is made by Mr. Wizard who used the data compiled by Komitadjie.
www.knifeforums.com/forums/showtopic.php?tid/904090/tp/7/


------------------------------------------------------------
(4) Some rough definitions, as I understand them:
Grinding: Abrasive particles bound in a hard matrix.
Lapping: Loose abrasives which are applied with a soft backing (like leather). The particles abrade as the roll around, and also as they embed into the softer material.
Polishing: Same as lapping, but done with much finer abrasive and used to get a mirror finish.
Burnishing: Mainly "smearing" of the surface with only minor abrasion (removal of material).

en.wikipedia.org/wiki/Abrasive_machining
en.wikipedia.org/wiki/Burnishing_(metalworking)

------------------------------------------------------------
(5) So far, I think that stropping is mainly an abrasive process. Abrasion always involves some burnishing, since dragging particles across the surface can push material around without necessarily removing material. During abrasion, probably the dominant process is removing material, but some incidental burnishing is likely or even common.

Like PhilipPasteur, I'm not yet convinced that burnishing is the dominant effect in stropping. But I'm far from sure either way. Consider the following example: water is very soft. But rushing water can exert tremendous forces. Similarly, if we have a miroscopic "peak" of metal, then what happens as leather "rushes" over it during rubbing? Especially if the rubber has abrasives embedded in it. Well... I have no idea. But it would be interesting to find out!

Not related, but I'm reminded of abrasive water-jet cutting which is used to cut stone and steel. The water jet is typically a mixture of water and garnet abrasive, and is travelling at a velocity of up to 3 to 4 times the speed of sound.
www.flowwaterjet.com/en/waterjet-technology/hyperpressure.aspx

------------------------------------------------------------

Okay, that's all I have for now.

Sincerely,
--Lagrangian

I'm also curious if anyone has tried one of the "rod-end boots"? It's been mentioned a few times in this thread, and there are links for where to buy it (such as eBay). Here is a company in Connecticut that sells them in several sizes. Looks like these are sold in packs of six.

www.sealsit.com/rodendboots.asp



It also seems that www.McMaster.com sells something similar, although it is designed for universal joints, rather than spherical rod-ends. They're called "bellows for universal joints."
www.mcmaster.com/#universal-joint-boots/=jr94tc



Sincerely,
--Lagrangian

Hi PhilipPasteur,

Oh, I didn't mean specifically for this test. Possibly a bad idea to etch for these tests, since we're interested in how the abrasive affects the surface, and don't want that confused with how the etching could affect it.

I was wondering etching might be useful in other ways. Maybe? Not sure.

Sincerely,
--Lagrangian

This is a very interesting question. Currently, it seems unlikely that any conventional knife metal could be sharpened as finely as obsidian. This is mainly due to the fact that metal is poly-crystaline. That is, it is comprised of many tiny crystals all packed together. It is difficult to get the knife edge to be much sharper than a single crystal. For example, take a knife made out of wood, and try to make it sharper than the wood-grain. You will find that as the edge gets close to the size of a wood-fibre, that the edge simply tears out, rolls over, or fails in some other way. Something similar to this happens with the tiny crystals in metal. These tiny crystals are sometimes called the "grain size" of the metal. I'm not saying it is impossible, but as you try to get sharper than the grain size, it becomes more and more difficult.

In material science, a glass is a material with no crystal structure at all. In other words, the grain size is zero. As a result, when a glassy material (such as obsidian) fractures, there is no grain size to limit how sharp the edges can be. So they end up very sharp indeed!

You might like one of my earlier posts in a different thread. I mention a list of sharpness and length-scales for different things, starting with hair and going all the way down to obsidian blades and the size of carbon atoms.
www.wickededgeusa.com/index.php?option=c...2&Itemid=63#4078

I think the sharpness of things is a very interesting question, so I'm always glad to see some discussion about it.

Sincerely,
--Lagrangian

wickededge wrote:


Wow.... pretty interesting. Would be neat to get an idea of how big those inclusions are, especially the ones that tear out, and their relative size to grit ratings.

I wonder what the inclusions are actually made of. Are they carbides, or slag impurities? Maybe someday, we can track down an metallurgist and ask.


btw, have you ever considered doing a metallographic etch of metal for your microscope samples? Hmm... maybe not a good idea after all, since some of those chemicals are pretty toxic...

Sincerely,
--Lagrangian

Hi Clay,

Wow! I'm fascinated by these photos.

In particular, I'm quite curious about what look like comets in your photos.... Dark spots with tails on them. I marked some on one of your photos:



Any idea what these are?

Sincerely,
--Lagrangian

Hi Clay,

After seeing your recent images, I've been wondering about the same thing. Probably we can apply some methods from Computer Vision to measure scratch widths. For example, there are open-source software libraries like OpenCV for doing computer vision.

I can't promise much, because I haven't much free time, and it's often not clear if the algorithms will give a clear and definitive measurement. The advantage is that an algorithm will give an unbiased answer. More precisely, if the algorithm is biased (such as a tendency to underestimate measurements), at least that bias will tend to be consistent and reproducible.

I'm reminded of the tennis player Andre Agassi. He complained that even the latest high-tech ball-tracking computers would make incorrect line calls. But he was consoled by the fact that the calls were made by a machine that has no bias as to who should win the match.

Sincerely,
--Lagrangian

P.S. For those with a technical background:
To analyze the images for scratch width, I have some general ideas right now:
(1) There are many papers about computer image-analysis in the medical industry. For example, given a tissue sample, these algorithms estimate things like the distribution of diameters of blood-vessles, etc.
(2) For scratch patterns which are parallel, maybe we could simply apply Fourier Analysis and look at the distribution of harmonic components in the frequency domain. It probably won't happen, but if we are _super lucky_ there would be a dominant peak at the average scratch size.
(3) There are various edge-detection methods in computer vision, such as the Canny edge detector, and things in computer vision called "snakes". A snake is basically a line or curve that is iteratively adjusted to find an edge or feature in an image. So it "wiggles" into position.
(4) There are a bazillion variants of these ideas, but we should probably just try the simplest ones (unless some of them are already implimented in free public packages, such as OpenCV).
(5) It can be tricky to estimate the accuracy and precision (ie: uncertainty) of the results, especially when we do not have test cases where we know ground-truth.
(6) Computer vision is much more difficult than would naively appear; many algorithms are extremely sensitive to signal-to-noise ratios, small changes in lighting direction, focus, and so on. Consider that in the 1960's, people thought computer facial recognition would be solved in a couple of years. It is only 40+ years later, that computer facial recognition is mature enough to be put in consumer cameras, and used in some security systems. And even then, facial recognition is often not reliable.
(7) Computer-vision might be the wrong tool for this problem. Instead, perhaps, measurements from a contact profilometer might be the most direct answer. If the contact-profilometer can show us the trace of a single scan-line, that would tell us a lot! Engineers in Surface Metrology must have good ways of doing such measurements.

Thanks Clay! It is super interesting to see those detailed measurements.

In one of Clay's images, he has very very tiny annotations. I can barely see them, and they are unreadable to me. I took Clay's image and marked where I see the annotations in red.

Clay's original image is here.

This is the same image with the areas of interest marked in red:


I was hoping to read what these were. Are you guys able to read these? I'm using Internet Explorer 9 in Windows 7.

Sincerely,
--Lagrangian

Hi Clay,

Wow, that last image is amazing! More please.

btw, I think the forums are re-sizing your images, so the measurements/annotations you made to the image are too small to really see or read. Is there a way for you to show us those images without so much resizing? Maybe post them to your blog and then link that?

You also mentioned that CoorsTek gives measurements for surface-roughness of their ceramics in Ra. I'm not sure how they do those measurements, but I'm feeling unsure that they would use a contact profilometer to do it. This is because the extremely hard abrasives might wear out the stylus. The stylus that is dragged over the surface needs to be very sharp and precise. If it were dragged out along any very abrasive material, I think it would be damaged, or at least worn out. Maybe it's a diamond stylus. I don't know.

My guess (just a guess!) is that they use some type of non-contact profilometer to do their measurements. Since they are a huge company, one of the largest producers of technical ceramics, I would suppose they have invested in high-end optical (non-contact) profilometers and other fancy machines for doing surface measurements. Don't know if they would tell you, but maybe you could ask them out of curiosity?

If you don't mind me getting a bit philosophical:

I also only recently learned about profilometers. I call this an example of not-knowing what I don't know. For example, I don't know how to speak German, but I know enough to realize that, and I also know where I could go to learn to speak German. This is an example of knowing what I don't know. I think this is an important point for two reasons:

If I know what I don't know, then:
(1) I know how to gain more expertise.
(2) I can begin to assess my own level of expertise.

It's very difficult to do (1) and (2) if you don't know what you don't know. There is always trial-and-error... But it's probably better to leverage huge areas of research which have already been done.

One way I'm trying to figure out what I don't know, is to read up on engineering. Engineers and manufacturers have had to measure cutting performance, material strength, friction, and surface properties for centuries (even if you start counting as late as the Industrial Revolution, not to mention the ancient Egyptians). So along these lines, I've been browsing engineering, manufacturing, and science topics in places like Wikipedia, research papers, the library, YouTube, Amazon.com, and company websites. Ideally, it would be great to also do some sharpening tests, and talk to knife makers, etc.

I would humbly invite others to do the same, and then share with us what they find.

Sincerely,
--Lagrangian

Hi Clay,

Have you considered a contact profilometer at all? It's a device used to measure surface-roughness, and is typically used in some metal-working and/or machine-shops. It runs a tiny stylus over the surface and reports back a numerical measurement. The "advantage" is that while it is very expensive (thousands of dollars), it is not insanely expensive (like an scanning electron microscope). The downside is that it returns numbers, not an image. Or, I suppose, it may return a single line of data as a graph (ie: a 2d plot where x-axis is horizontal position of the stylus and y-axis is the stylus height). So it's not as simple to interpret the results. And if the surface is directional (like lots of parallel scratches), then the scanning direction will affect the results.

There are non-contact profilometers; they're typically based on light scanning. But non-contact profilometers are insanely expensive (at least from what little I've heard).

I know almost nothing about profilometers, except what I've read on wikipedia:
en.wikipedia.org/wiki/Profilometer
en.wikipedia.org/wiki/Surface_metrology

Example of a contact profilometer by Mitutoyo (high quality Japanese company):
www.amazon.com/Mitutoyo-178-561-02A-Surf...=pd_sim_sbs_indust_1

Probably not worth buying. But if you have any friends who work in a lab for manufacturing, machining, or metrology, it might be worth asking them for a favor?

I kind of got curious about metrology in general, and got sucked into browsing Wikipedia for hours and hours.

Sincerely,
--Lagrangian