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Sharpening Diamond Microtome Knives

Joe Gwinn

Stainless
Joined
Nov 22, 2009
Location
Boston, MA area
I always wondered how one sharpens diamond microtome knives, which are used to shave biological samples off into slices maybe 100 nanometers in thickness (about 4 microinches), for examination with an electron microscope. For the record, the wavelength of green light is about 530 nanometers.

This is well finer than any diamond polishing grit, so how is this done? It turned out to be a bit of a surprise.

The polisher is a very well balanced small flat-faced iron disk charged with very fine diamond paste, spinning at 50,000 to 100,000 rpm. At this speed, any bit of diamond blade sticking up is burned away. The principle is like a surface grinder sparking out.

So, the inventor inverted our usual observation that there should be no sparks with diamond, because the diamond will be destroyed.

The inventor is from Venezuela.

Diamond knives are also used in such things as eye surgery.


Diamond knife - Wikipedia

See reference [1] for the patent, which is in English. British patent 799,498 published in 1958.
 
Not really inverting anything, the "no sparks" thing is for when using diamond abrasive on steel... And I kind of thought this would be common knowledge - I learned about how diamond abrasive was charged in a lap to cut diamonds a very long time ago when I first learned how jewelers cut and polish facets on a diamond.
 
Not really inverting anything, the "no sparks" thing is for when using diamond abrasive on steel... And I kind of thought this would be common knowledge - I learned about how diamond abrasive was charged in a lap to cut diamonds a very long time ago when I first learned how jewelers cut and polish facets on a diamond.

Yeah, but facet cutting is low speed, probably in olive oil.
 
Not that low. As I understand it, polishing is generally done at lower speed, cutting at higher speed. Still, you're correct that the speed is not as high as this patent mentions. I think this method is pretty old though, probably not done that way anymore.
 
Not that low. As I understand it, polishing is generally done at lower speed, cutting at higher speed. Still, you're correct that the speed is not as high as this patent mentions. I think this method is pretty old though, probably not done that way anymore.

Yes. I recall a recent video on diamond cutting, where faceting was done on a horizontal copper disk charged with diamond dust coated with "sweet" (olive) oil. I don't recall that they said how fast the copper disk rotated, but it did not throw oil off the edge.

As I recall, glass-cutters at the Waterford factory in Ireland used much the same process to cut lead crystal glass, except that the copper tool was shaped to cut surface grooves.
 
I did a little looking through some related patents yesterday, one more recent one brought up using a specially prepared (via "glow deposition," some sort of plasma process) silicon dioxide! as a lapping abrasive on diamond! Interesting. The actual sharpening mechanism is somewhat similar I think to the one you initially referred to, as the patent circumferentially mentions removing diamond molecule by molecule.
 
I did a little looking through some related patents yesterday, one more recent one brought up using a specially prepared (via "glow deposition," some sort of plasma process) silicon dioxide! as a lapping abrasive on diamond! Interesting. The actual sharpening mechanism is somewhat similar I think to the one you initially referred to, as the patent circumferentially mentions removing diamond molecule by molecule.

Interesting. What is the patent number or numbers?
 
US 4,581,969. It also refers to another that has some further info. And it was "atom by atom" removal, not molecule... I always switch those. Absentmindedly.
 


Yes. I recall a recent video on diamond cutting, where faceting was done on a horizontal copper disk charged with diamond dust coated with "sweet" (olive) oil. I don't recall that they said how fast the copper disk rotated, but it did not throw oil off the edge.

As I recall, glass-cutters at the Waterford factory in Ireland used much the same process to cut lead crystal glass, except that the copper tool was shaped to cut surface grooves.



When we toured the Waterford factory in Ireland, everyone else on the tour was fascinated by the small 5 axis CNC grinders doing the work on the "cheap" stuff. I see that kinda thing every day. I was more fascinated to watch the old guys doing the fluting by hand with the grinding wheels. And watching the difference between the 50 year old guys and the new apprentices. Neat stuff.
 
When we toured the Waterford factory in Ireland, everyone else on the tour was fascinated by the small 5 axis CNC grinders doing the work on the "cheap" stuff. I see that kinda thing every day. I was more fascinated to watch the old guys doing the fluting by hand with the grinding wheels. And watching the difference between the 50 year old guys and the new apprentices. Neat stuff.

When my wife and I were there, no CNC machines. But it certainly makes sense. The 50-year-old guys we watched had no problem carrying on a conversation while cutting flutes using graceful fluid motions.

 
US 4,581,969. It also refers to another that has some further info. And it was "atom by atom" removal, not molecule... I always switch those. Absentmindedly.
Crystals as such don't have Molecules, The Atoms form the crystal lattice.
...lewie...
 
what might be the edge radius of the "diatome" knive?
 
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I have seen them for sale commercially at 2nm edge radius. And have read scientific papers doing experimentation that achieved 0.1-0.3nm edge radius but not repeatably.
 
atomic radius of carbon is around 0.170 nm. how does 0.1 nm work? you cant grind the atom, right? btw, i assume carbon doesnt produce a burr. would be hard to get rid of it at these dimensions.
 
atomic radius of carbon is around 0.170 nm. how does 0.1 nm work? you cant grind the atom, right? btw, i assume carbon doesnt produce a burr. would be hard to get rid of it at these dimensions.

Hmm, sure about that? Google says atomic radius of carbon is .0914nm.
 
... I was more fascinated to watch the old guys doing the fluting by hand with the grinding wheels. And watching the difference between the 50 year old guys and the new apprentices. Neat stuff.
An art that I could never do.
Dad had a deaf guy who could do this on the teeny tiny cutting tools and burrs so repeatability.
Things that a five or six axis sub micron positioning cnc has problems with even now.

How does one check a 0.1 nm edge and know? We are so way past optical.
The SEM I had would not go anywhere near there. TEM also questionable.
So how is this done?
Bob
 








 
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