The dark art of diamond sharpening

[Estrada]

Hi all,

About 2 or 3 years ago I made the jump from embossing with sapphire cones to cutting with a diamond stylus. This coincided with the construction of my first stereo cutting head. It very soon became clear to me that I would not be going back to embossing as the results were so much better with diamond cutting. I knew this was where I wanted to be. I soon also came to the realisation that if I wanted to continue with this hobby I was going to have to work out how to sharpen these things myself as I just couldn't afford to buy a new one or even get the old one sharpened every time I chipped a diamond, which early on seemed to happen frequently. So about 2 years ago I started down the path of sharpening my diamond styli.

I'm going to start off by saying that I am by no means expert at this and my methods and equipment are fairly crude. I'm sure there are better ways of doing it than what I currently do, but I'm still learning and trying things and hopefully the results will be better (and faster) over time. I also have no intention of doing this commercially at this stage because a) I don't think my skill level is high enough yet, and b) at present it takes too long to be viable.

All that said though, I am successfully making diamond styli which are able to cut to a level of quality I'm happy with.

Here are a couple that I've recently made.

Photo on 18-03-2025 at 1.48 PM.jpg

The shanks are made with 1.6mm aluminium TIG welding rod which contains 5% magnesium which makes then a little harder. I make the shanks on a hobby lathe (Emco Unitmat 3) which is a great tool for this kind of thing. I've not yet tried making Neumann style shanks but at some stage I will give this a try. The diamond blanks are 0.6x0.6x5mm CVD (chemical vapour deposit) synthetic diamond. These are available from a few places in China. If you look around you can find them quite cheap. You can buy them as rectangular blanks or pre-cut to the basic stylus shape. Having them pre-cut adds quite a bit to the cost so I just buy them as rectangular blanks and do the cutting myself. The blanks appear to be laser cut from a sheet of diamond so they have 2x mirror polished faces and 2x rough cut faces. This is generally fine, all you really need is one mirror polished face.

IMG_7437.JPG

I'll get into a bit more detail on the equipment and process in later posts. It would be great to hear from anyone else who may also be doing this and share tips, experiences etc. It has certainly been a journey, probably more difficult than actually getting my lathe up and running. Here are a couple close up photos of the diamonds in the picture above. I will post more soon.

Photo on 10-01-2025 at 2.10 PM #3.jpg

Photo on 18-03-2025 at 2.14 PM.jpg

[Estrada]

Oops, the first close up image above is actually a sapphire (not one I've sharpened). This is the correct image

Photo on 18-03-2025 at 1.52 PM.jpg

[markrob]

Hi Estrada,

This is awesome work! Some time ago, I've played with making carbide and sapphire cutting styli with a home made template faceter with some limited success. Template faceting is very inexpensive, but not very precise. I stopped working on this long ago and have been embossing ever since, but might be interested in taking it up again based on the results you are getting. Can you provide a list and approximate cost of the equipment you ended up using? I would be in the same boat as you, strictly DIY hobby mode.

Mark

[farmersplow]

Hi Estrada,

it's a good idea to start this post. Thanks for it.
It is a great challenge and you have already achieved great results. I'm looking forward to more!
I myself have had some experience with cut diamonds, although the cutting was done by a friend of mine (a former jewellery maker). Unfortunately I have very little time at the moment, but I will be happy to share my experiences with this (and the production of 320 stylus holders) in the future.

Greetings from Austria
Thomas

[Estrada]

Thanks for your replies Mark and Thomas.

As mentioned, my gear is pretty simple. I've built a small lapping machine which is powered by a relatively cheap 12v DC motor. It is wired up to rotate in either direction and has a speed control. Max speed is around 3500 rpm. It looks like this;

IMG_7438.JPG

This machine has been messed around with quite a bit. It was initially belt driven and I tried a number of different bearings for the main shaft. For quite a while I was using part of an old sewing machine for the main bearing/shaft. Eventually I switched to direct drive which has been much more successful as there is a lot less vibration. I will likely rebuild it entirely at some point as I would like to make the top surface with 10mm steel or iron, instead of the 6mm aluminium. This will give the machine more weight and stability. Vibration is the enemy.

At this point I'm using 2 different types of diamond grinding discs. The small white ones on the left are ceramic bonded diamond grinding wheels. I have a few different grits (400,800,2000,10,000), the courser grits are used for forming the rough shape. The 400 removes material very quickly but it is far to rough to form a decent edge. The 800 and 2000 will get closer. The 10,000 is then used to form the edge. The 10,000 can get very close to a usable edge but not quite. For the final polish I use the larger disc which is a 50,000 grit (0.5micron) resin bonded disc. I use this at a relatively low speed to do the final polish and get the blade edges sharp.

This process is quite slow. At best it would take me between 1-2 hours to shape a diamond from blank, working through the different grit ceramic discs, and getting it ready for the final polishing stage. The final stage is the slowest part. Usually I will set things up and leave the machine running while I go away and do something else. Often I will leave it for around half an hour before checking. The amount of time it takes for the final stage varies quite a lot, but usually there would be a few hours involved, though mostly it's just setting up the machine and leaving it. Then it is a matter of grinding, inspecting, grinding, inspecting until I can't see any defects. I then give it a quick test cutting a silent groove. If there is any hiss in the grooves I usually keep going. Often I've had hiss in one channel and not the other, indicating that one side is good and one needs further work. The good thing in this situation is that I know which side needs more work.

The other key piece of equipment is the faceting manipulator. The one I'm using can be bought relatively cheaply off aliexpress. There are better options out there and I will likely upgrade to something better engineered at some point, but this is working for me at this point. It has a 96 position index wheel which allows you to control the grinding angle accurately. It has had a couple of crude mods - one to allow it to be adjusted up and down and another to provide some control of the weight/downward force of the diamond on the disc.

IMG_7441.JPG

Above is a photo of the faceting manipulator and a 3D printed guide I made to set the angle between the arm and the disc. This angle, combined with using the correct angles on the index are key to ensuring a 90 degree tip.

The next line of exploration will be using a cast iron lap. A friend of mine is experimenting with this at the moment and getting some promising results. I've made a lap out of 80mm diameter cast iron, however I need to fit an additional motor which can achieve much higher speeds than what I can currently do. I'm hoping to use this for the final polishing stage, hopefully it will be faster than the resin bond wheel. I should also be able to go down to a finer grit such as 100,000 (0.25 micron) and get an ever sharper edge.

IMG_7442.JPG

That's a bit of a quick overview. I will aim to post a bit more detail on the process including grinding angles etc. soon. Feel free to send through any questions.

Thanks
Craig

[farmersplow]

Hi Craig, that's a fantastic design. This is what DIY should look like. Focused on the essentials! You only have to screw in the one wood screw at the front . But joking aside, it's really great.
Thank you also for describing your approach. The improvements you have planned can certainly further improve the end product. I'm already looking forward to seeing how things progress.
Thomas

[jjwharris]

I'm interested to see what others have to say on this topic - I tried using ceramic bonded discs, but found the removal rate was too slow - or maybe I'm too impatient, as it seems like Estrada is getting usable results with a bit of patience...

After experimenting with ceramic bond discs, I put the project on hold as I found the progress too slow. I now have a machine together using a VFD spindle and a cast iron grinding disc. The cast iron disc did need to be dynamically balanced on the spindle to take out any vibration, it spins at ~7000-9000rpm, which results in a 36-37 m/s surface speed. Surface speed seems to be important to quick shaping of the diamond.

DiamondGrinder.jpg

This is a photo of the diamond grinder - it looks 3d printed, but there is an internal aluminium structure and the voids are filled with 20kg of concrete to dampen vibrations. I've been using a mixture of 1000+3000+10 000 diamond grit. It takes ~3 minutes to create a facet, I've included a photo.

Diamond.jpg

You'll also notice there's only one facet...The diamond kept slipping in the holder, as I don't think it can sustain the heat from the cast iron disc, so I'm putting this to one side until I can purchase the correct tool holding.

I thought I'd upload perhaps the most helpful pdf I came across during this process - it covers quite a bit about surface speed and pressure required.

You'll notice in the image of the grinder I uploaded, I have an automated carriage and crude weight adjustment system - I ended up not using this, I think it could work, but it would probably require some sort of dampening. I've had more success moving the carriage by hand, I'm assuming there's some form of dampening happening when it's moved by hand.

I'm intending to make a second grinder - That grinder would be specifically for 50-100k diamond grit and the final polishing stage, but I need to make some more space to keep the roughing and polishing grinders separated to avoid cross contamination.

[Estrada]

You only have to screw in the one wood screw at the front .

I'm pretty sure that wood screw was serving a very important function at one point

Thanks for sharing your work jjwharris. I'm very keen to pursue the iron lap option. I think this is probably the way to go in the long run, for the final polishing stage at least. While the resin bond disc does work, it is slow and I think from what I've seen of your experiments the iron lap will speed things up.

Thanks for all the comments so far, I will post more soon.

[Thelatheofus]

Cheers for this thread, really interesting read !

I was thinking what would be the most appropriate regular machining gear that could be adapted for this use ? Surely the cheap diamond polishing machines available on aliexpress are far from suitable for this work ?
Would adapting a lathe spindle horizontally make sense for this ?

[Estrada]

I was thinking what would be the most appropriate regular machining gear that could be adapted for this use ? Surely the cheap diamond polishing machines available on aliexpress are far from suitable for this work ?
Would adapting a lathe spindle horizontally make sense for this ?

There are better lapping machines out there than those cheap aliexpress ones. A lathe could certainly be adapted, jjwharris essentially built a lathe specifically for this purpose, see above post. I've also seen routing tables which could be adapted. It should be something reasonably heavy as this will minimise vibration. The one I've built really would benefit from more weight. The other factor is what speed it can achieve, this will dictate what type of grinding disc could be used. I've even seen old valve (automotive) grinding machines which I thought could be adapted for this purpose. Heavy and well engineered is probably what you are after.

[Estrada]

've played with making carbide and sapphire cutting styli with a home made template faceter with some limited success. Template faceting is very inexpensive, but not very precise.

Hi Mark,

I wasn't sure what you meant by template faceting so I looked it up. I think this could actually work for sapphire as it is a lot softer and easier to work with. I've only played with sapphire a small amount but it grinds quite quickly. When I've done things like grinding the burnishing facets I've ground the stylus by hand with the lapping disc stationary in order to remove only a fine amount. The template technique could be handy for that.

Cheers
Craig

[markrob]

Hi,

Sapphire what I was working with at the time and it did grind very quickly. I was surprised at the times you were quoting with diamonds. Also my lapping setup was much cruder than yours. I think you did a very nice job getting that together. I'll say on top of this thread and I just might take this back up again using some of your techniques.

Mark

[Estrada]

I was surprised at the times you were quoting with diamonds.

Diamonds do take a bit of time, well using my method at least. I think CVD takes longer than natural diamond, though I think I've only had one natural diamond stylus and that was a while ago. I'm fine wth this for now but it would be great to be able to do it quicker. I think that cast iron will be a lot faster. The options with iron seem to be a smaller lap like jjwharris is using at high speed (somewhere above 7000rpm) or a more typical 300mm iron lap at 3000rpm. The larger lap would need a larger, heavier structure to keep it stable. I intend to experiment with iron soon so I will report back once I've had a go. My initial idea was actually to repurpose a cast iron brake disc from a car, it might be possible but it would be far too big for the table I have built.

[zdenek]

Great photos!

[zdenek]

I was surprised at the times you were quoting with diamonds.

Diamonds do take a bit of time, well using my method at least. I think CVD takes longer than natural diamond, though I think I've only had one natural diamond stylus and that was a while ago. I'm fine wth this for now but it would be great to be able to do it quicker. I think that cast iron will be a lot faster. The options with iron seem to be a smaller lap like jjwharris is using at high speed (somewhere above 7000rpm) or a more typical 300mm iron lap at 3000rpm. The larger lap would need a larger, heavier structure to keep it stable. I intend to experiment with iron soon so I will report back once I've had a go. My initial idea was actually to repurpose a cast iron brake disc from a car, it might be possible but it would be far too big for the table I have built.

https://www.instagram.com/p/CsTNcCAgfWG/

For finishing polishing, use a rubber disc with a 0.1 micron diamond paste, you can get it from a jeweler who cuts diamonds.

The video shows a Russian with his diamond knife grinder, not my device, but we have similar ones, only factory ones.

[Estrada]

For finishing polishing, use a rubber disc with a 0.1 micron diamond paste, you can get it from a jeweler who cuts diamonds.

A rubber disc? I've not come across this before.

I'm familiar with Vinylium's work. In fact, my method is based on his earlier work and instructions. He has since moved on to polishing his diamonds with metal bonded grinding discs, running at high speed (around 9000 rpm I think). I think he is using 10,000 grit discs. His work is very impressive, and he seems to be able to polish diamonds very quickly. For me, the cost of the metal bonded discs was prohibitive, I would also need to build new machines similar to his which might still be a bit beyond my skill set. Great work though, I'd encourage anyone interested to check it out.

[zdenek]

I saw this at a jeweler's [of course these are jeweler's secrets and no one wants to brag about them publicly].
If you have a hard rubber 1-2 mm thick, carefully stick it onto a metal grinding disc and lubricate it with 0.1 micron diamond paste for polishing precious stones and diamonds and you will see a great effect! When polishing with a rubber base, the diamond blade will NOT CRACK accidentally under stronger pressure.
Basically, when polishing, the knife floats on a diamond disc with a rubber backing and the diamonds of the paste only lick the cut diamond, such is the circus...

The spindle is expensive [the Russian spindle probably has air bearings], there may be oil bearings under pressure with a car pump, for example [you need to make a labyrinth seal so that diamond dust does not get into the bearings and the grinder shaft]. Such a machine is not expensive to make. It is better to make it from cast iron bases and steel, it will be more accurate and stiffer.

[discosdecorte]

I dont understand the half you are talking about but damn I love this thread!

Fer

[juba bc]

Hi, I did this experiment using a car brake disc, it's not as flat as I imagined and it was necessary to make some corrections, but it worked, I made some points successfully, I still can't get a perfect sharpening without any noise but I believe that more dedication is needed, and I hardly have time for that. As soon as possible I will put the project images here, I have no intention of working with stylus sales

[juba bc]