The dark art of diamond sharpening

[Estrada]

@ stylus maker, are you polishing the mirror face of you diamonds? I'm relying on the factory polishing from the diamond supplier but I think this is not as good as it could be. If so how are you holding the diamond to do this?

[Fela Borbone]

Great thread!
Thanks a lot, Estrada and other trolls posting here and sharing..This is gold.
I made tungsten point stylus for embossing, worked great., Tried diamond but my results were not good... slow coarse grinding and bad finishing. I used the wrong equipment, didn't dig too much, give up early, not much time avalaible... But after reading this, It's worth another try.
For bonding the tip, I use epoxi, but I dont make the mix 50/50. If adding double of "A" results in soft product. Double of "B" we get harder, less elastic mix(what we wont).Too much B, makes it too brittle, so, some experiments should be made. The "A" in my brand, may be the "B" in yours...Some epoxies are good at standing heat.

[Fela Borbone]

By the way, another Emco Unimat 3 here, I used it to make carbone fibre shanks, but I'm back to aluminun...

[Fela Borbone]

...but now I do this job by hand with a bricollage drill, regulating the speed gripping the chuck with a leather glove..

[Stylus Maker]

Yes, but if your only polishing for yourself,its lnot realy nessacary. As a maker and seller Im required to do stylus at a very perfect leval.

[Estrada]

Yes, but if your only polishing for yourself,its lnot realy nessacary. As a maker and seller Im required to do stylus at a very perfect leval.

Thanks for that. I do find that the quality of the face polishing can vary so I would like to be able to do this. Do you have a special tool you use to grip the diamond?

@Fela Borbone thanks for sharing, great to see what others are up to. The unimat 3 is such a great little lathe, I've been able to do so much more with this hobby since getting once of these. I did have to replace the motor on mine, I'm running it off an old washing machine motor which has a lot more torque than the original motors.

[Stylus Maker]

Front polishing is the most dangerous process. As Im using a coburn diamond spindle and turbo scaife supported by a 20mm thick steel bench(should be 40mm). Ive micro balance and ultra flattened my scaife then polished it. If you dont have these in place you need to choose from the 4 ends of the stylus to find the best one for the front.
If you insist you need head gear and safety glasses for when a slight mistake happens.Double scotch on standby helps. I use a bowl dop for holding baguette diamonds.
HDPL item code : GD5 get the heavy tang. Good luck.

[Estrada]

Front polishing is the most dangerous process. As Im using a coburn diamond spindle and turbo scaife supported by a 20mm thick steel bench(should be 40mm). Ive micro balance and ultra flattened my scaife then polished it. If you dont have these in place you need to choose from the 4 ends of the stylus to find the best one for the front.
If you insist you need head gear and safety glasses for when a slight mistake happens.Double scotch on standby helps. I use a bowl dop for holding baguette diamonds.
HDPL item code : GD5 get the heavy tang. Good luck.

Thanks for your advice on this. I might be a while away from trying this as I don't have the equipment, except for the double scotch

[symatic]

this is really cool to see. awesome work. I've been to Vinilyum's workshop and he is indeed doing very awesome stuff. I"m really glad to see a more DIY approach getting such good results too, very encouraging!

[Estrada]

Been meaning to post this for a while. This is my somewhat crude jig for mounting diamonds into the shank.

IMG_7448.JPEG

It's just a piece of aluminium with a hole for mounting the shank. The grub screw in the side locks the shank in and positions the index in line with the horizontal line scribed in the top of the aluminium block. I then use this line a a visual guide to get the diamond aligned with the indexed surface of the shank. It's not entirely accurate but it is good enough for now until I find a more precise method. Interested to know how others are approaching this.

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[jjwharris]

I had these holders arrive from aliexpress - they do a much better job than the brass ones I had.


They dont screw, so I mounted them into my usual homemade dop and had a thread so I could push a couple of nuts up into the ring to keep clamping pressure constant.

I've started working on this again, a few changes - mainly the tool post is a lot better and more rigid, along with the angle selector.

I'm putting this out there as I'm at a bit of a loss..I'm thinking it has something to do with grain, or maybe the cast iron I have - I guess this is the 'dark art' bit.

When I'm grinding, if I grind into the cutting face (as I expect it should be...) the scaife does blacken as I've read and expect, however there is very little, if any, material removal.

I've got a theory that my cast iron may be off - This is what it is made from.

Carbon C 3.55
Manganese Mn 3.55
Silicon Si 2.50
Nickel Ni 0.03
Chromium Cr 0.02
Molybdenum Mo 0.01
Phosphorus P 0.10
Sulfur S 0.01
Magnesium Mg 0.04
Copper Cu 0.05
Iron Fe Balance

Compared to HB460 Cast Iron, which is used in the 'Wittocx USA600 Turbo Super Special' (460HB, extremely hard, very fine pored alloy, general use, small stones, also for makeables)

Carbon
2.8%–3.4%
Silicon
1.5%–2.5%
Manganese
0.3%–0.8%
Chromium
8.0%-10.0%
Nickel
4.5%-6.5%

Untitled.jpg

Here's the scaife after making the above grinds;

scaife.png

Earlier I mentioned grinding into the cutting face...If I reverse the direction of the motor, material removal increases - I can almost cut a facet in ~5 minutes. The diamond edge does get chipped and another side effect is the scaife gets torn up, I can see bits of cast iron being gouged from it. I've tried;

Diamond powder + Beeswax
Diamond Powder + Beeswax Polish
Diamond Powder + Mineral Oil

I've tried embedding the powder with brass, hardwood, a roller bearing, so far nothing seems to make a difference.

Weirder still, I can't seem to finish a facet, it seems to stall at the same place.

I'm wondering if it is a grain issue, I've raised my tool to above centre, as I wonder if the grinding direction changes with height, in relevance to the direction of travel in the scaife.

I've tried to illustrate it in this picture;

Untitled4.jpg

Is this what the 'grain finding swivel' overcomes?

[zdenek]

For diamond grinding, several diamond discs with different granulation of diamond resolution are used.

Finish polishing, very precise diamond pastes with selected diamond powder are used, there can be no coarse grains. The grinding polishing disc is either brass lubricated with diamond paste or a rubber pad lubricated with a paste with precise selected diamond [the limit is 0.1 micron].

The disc revolutions during polishing are much lower than during grinding and are in the range of 50-150 revolutions per minute for mirror polishing. For ten polished diamonds, two well-polished ones are practically achieved.
If there are coarse diamond stones in a very fine polishing paste, the diamond stones will chip the tip of the blade of the ground diamond knife. Precision paste, 0.1 micron diamond polishing powder costs from $250 per 10 grams, and can be ordered from a diamond grinder.

[Stylus Maker]

Yeah... that to me is a grain issue. You need to grind a small triangular corner on the wheel contact point in grain direction first and go to cast iron with 50k powder. I like soy wax thinned with a little parrafin oil.Both facets on the blank have a very distinct grain direction almost in opposite to each other, and blade edge seems to be away from the wheel. Reversing the wheel shows you that you are close to the grain. I cant help any further as I work on a horizontal disc and cant comprehend the way your working in my head. try turning your blank upside down.

[jjwharris]

Cheers,

I tried removing one of the runners that feeds into the wheel - this gives me the ability to rotate the carriage around the centre of the carriage, without affecting the angle of the grind, I *think* it's working/helping to find grain.

In this image the big facet I managed tio grind really quickly (5-10 minutes) - surface speed wise I started at 1570.80 m/min (1500 rpm on a 12" Scaife), then went a bit quicker at 2261.95 m/min or 2181.78 RPM(12" scaife) which seemed to make it even quicker....

WhatsApp Image 2025-03-31 at 18.17.12_8bcc8c45.jpg

The second (weird!) facet took much longer, I think this could be a grain issue once again, caused by grinding geometry, or maybe the stylus isn't set correctly in the holder. It's 60 Degrees either side of the cutting face, with a 41 degree approach,

I would be interested to know what other peoples grinding angles are. I'd be even more interested to know if there is a calculation!

[zdenek]

The diamond guy https://www.instagram.com/reel/C-deBbZuO-6/ claims that he can make up to 80 knives in a day, it is unlikely that it is possible.

At my factory, a knife grinder with a diamond insert grinds one piece of a knife with an insert for about 1 hour, but the radius is larger because it is about 10 microns. On the other hand, for recording discs in DMM, a radius of no more than 1 micron is needed [for lauqcer a few microns].

I personally tried to make a knife and grind it for DMM on a professional machine and it took me as much as FOUR HOURS and it was not good at all ... So I do not know how to make 80 pieces in one day .... It seems to me that the machine will be for sale, that is what I understood from the description ...

[Estrada]

I believe this machine utilises metal bonded diamond grinding discs rotated at a very high speed. These discs are very expensive so I don't think I'll be going down that path as this is only a hobby for me. Looks like a good option if you are doing it commercially though. When I looked into these grinding discs, the finest grit available was 10,000 grit which is about 2 microns. This seems a bit course, though the different kinds of disc I have (ceramic bond / resin bond) of the same grit value behave quite differently so the metal bond probably behaves differently again. He does appear to get good results though.

[zdenek]

Recently, it has become a fashionable trend to raise money for so-called "startups", once it was a proverbial "pig in a poke", what I am getting at is that first you should do a survey, marketing of interest in diamond knives, then consider whether to do anything at all or close this job and run away from this problem and not have problems from potential clients. It's a hobby, but the road is an art ...

[jjwharris]

I believe this machine utilises metal bonded diamond grinding discs rotated at a very high speed. These discs are very expensive so I don't think I'll be going down that path as this is only a hobby for me. Looks like a good option if you are doing it commercially though. When I looked into these grinding discs, the finest grit available was 10,000 grit which is about 2 microns. This seems a bit course, though the different kinds of disc I have (ceramic bond / resin bond) of the same grit value behave quite differently so the metal bond probably behaves differently again. He does appear to get good results though.

I think this ties into that pdf I posted...It covers a reaction between Fe and Ni - Looking at the turbo scaife material composition, it looks like that has a relatively high nickel content too. It almost makes me wonder if Ni is the hero and not Fe.

[jjwharris]

I’ve tracked this down again, so I’ll post it as a bit of an info dump…

311B12DF-39B6-465E-B505-3FA0A0683EE3.jpeg

This is a chart of the material removal depending on grain orientation, too me, it looks like 110 would need to be flipped, whereas with 100, it should be fairly even on all sides, but the removal rate would be much lower?

It’s from this article here;

https://sci-hub.se/10.1016/j.diamond.2016.02.012


Anyway, I’m unsure if a complete and comprehensive understanding of the grain structures is entirely needed, watching this video;

https://youtu.be/gabs3CzYf54

I take it he is using the grain finding swivel in the very last moments, to find the correct angle?

[zdenek]

I stopped worrying about knives with artificial diamonds, because CBN is easier to grind with diamond discs and practically lasts on copper for the same amount of time, but diamond is 100 times more expensive, so for experiments I buy such used CBN knives [they turn hardened steel] for $ 10 for 10 pieces. As you can see, the CBN plate is fused into the carbide core, I pre-cut the size with diamond [$ 5 piece] discs - 0.2 mm, 0.3 mm etc., I gently pre-grind and then put the diamond knives in the grinding machine and tomorrow I will show you how it really looks and how long it lasts. CBN have different hardnesses from 8 to even 9.5 on the Morse scale, so you have to try it out experimentally, which one will be the best and hardest. I tried to cut a quiet groove in plastic, but in rolled copper it is much easierhttps://www.youtube.com/watch?v=5HygWphzvE4