Sharpening Diamond Microtome Knives

[Joe Gwinn]

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?

Transmission electron microscope - some can go to 50 picometers resolution.

Electron microscope - Wikipedia


An atomic force microscope would also work, and is far simpler and cheaper.

Atomic force microscopy - Wikipedia

 

[Lewie]

H2, O2, etc.

Anybody ever heard of a Crystal of H ? :-) We were talking about crystalline form. :-)
...lewie...

 

[dian]

Hmm, sure about that? Google says atomic radius of carbon is .0914nm.

yes, thre are several different (types of?) radii reported for ellements, i dont understand the difference. but usually they are not that far off. surprisingly most ellements are 120-250 pm. e.g. i see iron as 156 or 194 pm.

Atomic Radius of All the Elements (Complete Chart Inside)

 

[Joe Gwinn]

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.

I read that and related patents.

I think I understand how SiO2 (silica) coatings can be used to lap diamond. The way one wins "metallic" silicon from silica sand involves coke (pure carbon), just as for smelting iron. So, Silicon atoms are perfectly willing to yield an oxygen or two to any carbon atom that it encounters. So, wherever the diamond work piece touches the rapidly spinning silica surface, the silica steals a carbon atom or two. It really does pluck carbon atoms away.

In this process, it does not matter that silica is softer than diamond - the effect is purely chemical. The remaining diamond will not be fractured or otherwise disturbed.

Another patent (us4581969) adds the twist of using the 111 crystal face as the cutting edge, and a different face (100 or 320) for the back, yielding a considerable improvement in cutting ability. One big advantage is the reduction of chatter.

 

[eKretz]

I read that and related patents.

I think I understand how SiO2 (silica) coatings can be used to lap diamond. The way one wins "metallic" silicon from silica sand involves coke (pure carbon), just as for smelting iron. So, Silicon atoms are perfectly willing to yield an oxygen or two to any carbon atom that it encounters. So, wherever the diamond work piece touches the rapidly spinning silica surface, the silica steals a carbon atom or two. It really does pluck carbon atoms away.

In this process, it does not matter that silica is softer than diamond - the effect is purely chemical. The remaining diamond will not be fractured or otherwise disturbed.

Another patent (us4581969) adds the twist of using the 111 crystal face as the cutting edge, and a different face (100 or 320) for the back, yielding a considerable improvement in cutting ability. One big advantage is the reduction of chatter.

Yeah that's how I understood it, so sort of similar to the first one you posted, just a little difference. The using different planes bit was pretty interesting also.

 

[Joe Gwinn]

Yeah that's how I understood it, so sort of similar to the first one you posted, just a little difference. The using different planes bit was pretty interesting also.

I think that the difference is that the silica will yield a sharper knife edge than the diamond-loaded iron lapping disk, because diamond lapping diamond involves a fairly violent impact, unlike the silica lap, where the effect is chemical in nature.

 

[eKretz]

Probably so, I would love to see what they're doing these days. Did you run into anything newer while browsing? That mid-80's one was the most recent I found.

Edit: I looked through some of the "cited by" and related patents and found something describing plasma deposition of carbon atoms in a manner where they could apparently make the blade directly to net shape, ready to cut, but didn't describe edge radius or whether it was as good as the other method.

I have been reading them since I last posted. It's very easy to get absorbed in reading patents and lose a few hours!

 

[Joe Gwinn]

Probably so, I would love to see what they're doing these days. Did you run into anything newer while browsing? That mid-80's one was the most recent I found.

I have not been looking, but I bet that there are various attempts to evade that patent. One way to tell is on Google Advanced Patents, to go through the later patents that cite this one. Usually, one can pick up a spoor that way.

I would guess that there are lots of metallic oxides that will gladly pluck carbon atoms off of diamond. Silica has the advantage of having a large technology for making silica layers, but it isn't the only one with that heritage. Nor is oxygen necessarily necessary.

 

[CarbideBob]

An atomic force microscope would also work, and is far simpler and cheaper.

This perhaps works not so well on a knife edge.

 

[jccaclimber]

I wouldn’t see if this is the same way tools for diamond turning are made? I’ve never looked at one past 240x, but they are visually perfect at that magnification, and priced accordingly.
It’s particularly difficult to machine steel with them due to the material being cut wanting to steal the carbon from the diamond tool, so this makes sense.

 

[mhajicek]

It's possible to sharpen an edge via etching.

 

[Scottl]

I always understood the sharpening process to be done with copper laps and ultra-fine diamond paste. Once heard a horror story about a lab tech who had just sharpened one and dropped it, creating a serious cut on her thigh. The process is done with horizontal rotating laps while seated. The machine resembles a phonograph turntable. I've seen a similar portable rig using replaceable disks used for in-shop sharpening of barber's scissors. The sharpening service came in and did a whole bunch while they still cut hair with other ones.

 

[Joe Gwinn]

This perhaps works not so well on a knife edge.

I've read of this being done, but don't know the details. An ATF scan is very slow and deliberate.

 

[dian]

It's possible to sharpen an edge via etching.

can you point me to some info on that? electrolytic or electroless?

(i dont think it would work on a diamond blade, though.)

 

[EPAIII]

I think when you get down to that level, the number you get will depend on a lot of things like the exact crystal or atomic structure and the measurement technique. When you consider quantum effects and the uncertainty principal, size can almost be thrown out of the window.

I am not surprised that different sources give different atomic radii. Or that the variations cover a wide range, perhaps as much as 2X, 4X, even 8X or 10X or more.

Hmm, sure about that? Google says atomic radius of carbon is .0914nm.

 

[Joe Gwinn]

I think when you get down to that level, the number you get will depend on a lot of things like the exact crystal or atomic structure and the measurement technique. When you consider quantum effects and the uncertainty principal, size can almost be thrown out of the window.

I am not surprised that different sources give different atomic radii. Or that the variations cover a wide range, perhaps as much as 2X, 4X, even 8X or 10X or more.

The covalent radius, meaning in this case the spacing between carbon atoms in a diamond crystal, is 69 picometers., which is close to 0.0914 nanometers.

Carbon - Atomic Radius - C

Note added on 19 Oct '21: One can measure the spacing between carbon atoms in diamond by means of X-Ray Diffraction.

X-ray crystallography - Wikipedia

 

[dian]

van der waals is 170 pm (if the source i quoted above is correct). whats the difference? 1:2.5 ratio.

as i understand it covalent is the distance of the protons in a grid. v.d.w. is looking at a single atom and trying to toutch /squeeze it and it would produce resistance at that distance. (then as to grinding the latter should be of importance. yes? no?

 

[eKretz]

van der waals is 170 pm (if the source i quoted above is correct). whats the difference? 1:2.5 ratio.

as i understand it covalent is the distance of the protons in a grid. v.d.w. is looking at a single atom and trying to toutch /squeeze it and it would produce resistance at that distance. (then as to grinding the latter should be of importance. yes? no?

Free vs. bound atoms, and many other factors involved. See here for some more relevant info:

atomic and ionic radius

 

[ttrager]

(Looks at his Spyderco folder sharpened by dragging it through a carbide bladed knife sharpener . . . and decides not to mention that) - Doh!