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 Post subject: Adamas Sintered Lap Review
PostPosted: Tue Jan 14, 2020 8:43 pm 
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Hello all!

I've been a long time lurker on these forums, but I finally thought it time to introduce myself and contribute to the community a bit.

A quick bit of my background: my day job for the past couple of decades has been in the world of materials, like at least a couple of others on this forum (Tom, Jon, I know -- probably a couple of others). I started my career in this working on sapphire for blue LED applications. We would sometimes look at these 50 pound crystals and talk about learning to cut them into massive gemstones. Well, one day, I had the saved up enough money to buy some starter equipment and give it a go! Twenty years later, I'm still doing it (minus a few years in there to get married, have kids, and such). After the sapphire, I went to a lab where I developed lapping and polishing processes for all sorts of different crystalline materials. SiC, GaAs, GaN, AlN, GGG -- throw the letters together, I have probably done it. SiC (you know it better as Moissanite, most likely) came calling then, and I went off to do that for a short while. It wasn't long until I was moved over to work on developing processes for diamond (it is used as an optic for very powerful IR lasers), since due to the gem cutting, I was the only person who had the slightest clue how it should be done. Nine years of that. Then cam another dive into the SiC again -- just the wafers had gotten bigger. This time, my mission was to introduce single-wafer processing and so much fixed abrasive as possible.

And so here we are today! It is fair to assume that my approach to gem cutting is toward the scientific side of things. It is also fair to assume I experiment a lot with different cutting and polishing techniques and am one of those who always like to try to latest thing. A lot of what I have learned in industry has made its way into the gem cutting -- but what may surprise you is how much what has been learned through gem cutting has made its way into industry. Charging plates for fine polishing -- used all the time for hard disk heads. Mixing oxides for polish has made its way into the latest CMP slurries. Using zirconia and chromium oxide for SiC was actually first done for gems (though I still use fine diamond for the gems -- gives me sharper facets!).

So right while I was pushing fixed abrasive for use in making SiC wafers, Adamas is coming out with sintered laps. Well. Had to try that. I contacted Tom and got 1 each of the 32M (coarse), the 12M, and the Twister 2. The first two are metal matrices, the Twister is a resin bond. I decided to test them out with a range of material First, some atrociously included Afghan "Hiddenite" (will, slightly green spodumene, anyway) -- a softer, fairly brittle stone. Next, I did a large chunk of moissanite (due to my career, I have quite a bit of it -- this one was over 10 years old, actually). This is about the hardest stone most of us will ever cut, though far from the toughest. Next I did two quartz crystals (let's see if we can gum one of these up!), then finally some tourmaline.

The Hiddenite: The 32M made extremely short work of getting this stone into shape. There was one massive flaw which normally I would cut out with a saw, but then this was a test. Running at about 1000 RPM with a heavy water drip, I was able to cut this from over 20 carats to a preform which would ultimately yield almost a 5ct stone in mere minutes. I let the speed do the work, keeping the pressure extremely light. Doing this, I found it very consistent. It is very easy to tell when the cutting stops -- the sound is quite distinctive. With the low pressure, there is no mast flex, and the meets were nearly there at just this stage with very little effort. These was no apparent gouging or chipping. I cleaned the lap with Lava soap, spun it dry, and oiled the iron. I tried the 12M for a few facets for fine cutting -- much cleaner than the 32M, yet still very fast. I slowed the lap down to about 700 RPM for this. After a few facets, I switched to the Twistor 2 -- now this was perfect. Mostly polished, just some horsehair scratches. The same fast cutting at low pressure and distinctive sound was still there. Achieving the meets took very little time. By the last tier, I was only checking meets at the end of the tier. This surface was polished very quickly using zirconia on the Darkside lap. About 10 sweeps per facets was enough. 32M to Twistor 2 to Zirconia on Darkside was extremely efficient. I never had to dress the laps.

The Moissanite: Normally, you might get 5-6 5 carat plus stones of this material using a 360 grit solid steel lap. After that, the lap will be hopelessly dulled, really only good for frosting -- it's fast cutting days are done. Of course, SiC for all its hardness is quite brittle, so the damage goes deep. There would still be a lot of work to go. The 32M shaped this stone far more quickly than anything I had used before, and at much lighter pressure, allowing for tight meets. Chipping was negligible. This was a pretty large stone -- started at 15 cts, ended at about 4.8. I cut Dr. Arya Akhavan's "Pedantic Sophistry" design for a couple reasons. First, it has some nice large facets -- a real challenge for a lap, and second, the three fairly sharp corners. If I am getting damage at the edges, here is where it will show up. I know from experience that resin bond does not work well on SiC, so I went to the 12M. Very fast, very tight meets. These wheels are exceptionally well balanced. Even with the high speeds, they run true and quietly. I was not sure whether this finis would allow a fast polish, so I prepolished some of the facets (the bigger ones) with 8k PCD on a Zinc plus, but left the rest. I polished the pavilion using the BA5T and 60k PCD (One of my favorite combinations -- fast, flat). The crown I did with the diamatrix and 100k PCD. One of my first attempts with that lap, too. I was quite pleased! Very fast. The facets I simply left as the 12M surface took 30-40 sweeps whereas the 8k facets took 10-20. Given the setup time and the possibility for error with all the indexing, likely best to just go 12M to the final polish in the future! That being said -- for some stones, knowing how to use charged plates will be essential. If these facets were any bigger, the 8k surely would have saved me substantial time. No dressing was required during the cutting of these stones.

The Quartz stones: Now here is where the background in materials becomes useful. I was pretty sure the metal bond wheels would load up quickly with this. Sure enough -- the 32M stopped cutting fairly quickly (had to know for certain -- I have been surprised before). To return the lap to good, this is the one time I have ever dressed the lap. Since then, it has continued to cut -- 4 stones since with no signs of slowing down. The Twistor 2 is resin bond, lower concentration -- just the trick! This cut nearly so fast as the 32M did on the Moissanite, still with low pressure. At the end of this, I had a surface which could quickly be polished with either zirconia or ceria on the Darkside again. 20-30 sweeps left a clean surface.

The Tourmaline: The 32M made short work of this one. The 12M was great until the hard direction -- got a bit of orange peel there. The Twistor 2 was better, but looking at the 32M surface, I decided that 8k on zinc was the way to go. Very fast pre-polish. This is one of the advantages of fixed abrasive -- used properly, the resulting subsurface damage is much, much lower. 5-10 sweeps with alumina on Darkside was all that was necessary after this.

So the summary:

These laps produce clean, low damage surfaces. They are extremely flat and true and allow for using very light pressures, making achieving tight meets much easier with less checking.

There is an element of "the right tool for the job" here, though. The metal bond 32M and 12M are ideal for hard, brittle materials. As materials become softer and tougher (gummier), the Twistor 2 becomes preferred for even the cutting. A hard, relatively tough material like sapphire should do quite well on the 32M and 12M, though it may load the laps a bit more than the Moissanite did. Some materials will still polish much more easily with a standard charged lap prepolish (3k or 8k on BATT or 8k on Zinc -- the latter being not the most popular, I know, but it remains one of my favorites for very flat facets!). These laps will still save a great deal of time in getting to that stage, however, and then reduce how much must be removed in that stage to eliminate the subsurface damage.

Next up, going to try some sapphire -- see if my prediction is right! Has anyone else tried these laps? What were your experiences with these? I would be thrilled to hear about it!.

Picture of the finished Moissanite included below. 4.8ct!

Attachment:
Moissanite 1 - Forceps 1.JPG
Moissanite 1 - Forceps 1.JPG [ 778.77 KiB | Viewed 2067 times ]


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 Post subject: Re: Adamas Sintered Lap Review
PostPosted: Tue Jan 14, 2020 9:59 pm 
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Welcome! I must say you entered the forum with an exciting post. The science of faceting is not often presented well or at all. I'm looking forward to your further contributions.


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 Post subject: Re: Adamas Sintered Lap Review
PostPosted: Wed Jan 15, 2020 6:40 pm 
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Wow, thanks for the detailed reviews! This is great information for anyone thinking of getting one.

-Allan

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 Post subject: Re: Adamas Sintered Lap Review
PostPosted: Wed Jan 15, 2020 11:57 pm 
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I am a big fan of Toms Sintered laps. They are my most used laps these days. A number of my students also have them and all are very happy with them.


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 Post subject: Re: Adamas Sintered Lap Review
PostPosted: Thu Jan 16, 2020 6:46 pm 
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A couple other quick notes on these:

Tom gives detailed instructions on the proper care of these laps -- it is well worth it to follow these closely. The note about "no, you can't use a SiC dressing stick and expect a refund" cracked me up. Big no-no, there. Alumina only. Also note the oiling -- the bases will rust. Want to keep them clean!

So how far could this style of lap go? For the metal bonds, they could potentially go a a particle size of 1-2um, though that starts to get difficult. The concentration would have to go down, most likely (though the number of particles would be higher with the smaller grit, so still worth it), and even the benefit of doing this is questionable outside of very brittle stones. For tougher stones (quartz, sapphire), this really would not be useful.

Now, if you want to produce something which would qualify as a polish with this technique, then a vitreous bond wheel would be the way to go -- 1um-0.25um, depending on the material. The trade here is the laps will wear far more quickly than either the metal bond or the resin bond. The finishes using such wheels (0.25 is typically designated a 60000 grit, or a 60k wheel) are truly amazing, though. Again, purely the province of brittle materials, going this far. Would work well on Moissanite, likely garnets, chrome diopside, kunzite, etc.


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 Post subject: Re: Adamas Sintered Lap Review
PostPosted: Sun Jan 19, 2020 3:04 pm 
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icurrier wrote:
A couple other quick notes on these:

Tom gives detailed instructions on the proper care of these laps -- it is well worth it to follow these closely. The note about "no, you can't use a SiC dressing stick and expect a refund" cracked me up. Big no-no, there. Alumina only. Also note the oiling -- the bases will rust. Want to keep them clean!


This seems very contradictory. In your review you mention cutting a large moissanite (SiC), so wouldn't you have just "ruined" your lap by putting SiC on it? I've never heard of SiC dressing stones damaging sintered laps. Many manufacturers seem to recommend SiC dressing stones.

I realize there's some difference between the polycrystalline bonded grit of a dressing stone versus SiC grown as a transparent monocrystal, but as you mentioned, moissanite is quite brittle, and some small grains would chip off during cutting and create at at least a little "grit".

I'm curious as to why moissanite gems are okay but dressing sticks are not.


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 Post subject: Re: Adamas Sintered Lap Review
PostPosted: Tue Jan 21, 2020 8:29 am 
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Does seem odd, doesn't it?

The dressing primarily affects the bond, removing the dulled diamond and loaded voids, allowing free cutting again. SiC is a fair bit harder and more friable than alumina. Also, it is typically used at much coarser grits than alumina. Most often, SiC dressing stones are used for saw blades -- think 60-120 grit. These sintered laps would be more equivalent to 600 grit+.

If someone were to indiscriminately use an SiC dressing stick on these, it would overcut the bond, leaving the diamond excessively exposed and contaminate the lap with very large and friable SiC grit from the dressing stick. The SiC grit would break down fairly quickly, if using a hard, tough stone. One a softer stone, the impacts of these could last longer. This grit is also loose on the surface of the lap, since it is too large to really get stuck away in the pores. Loose abrasive is exactly what these laps are designed to avoid. The excessively exposed, poorly bonded diamond is also liable to come free, leading to a large, rolling diamond particle. Ever see a deep scratch take looks like a connected series of pits, often with a fainter, near parallel trail along it? That is the telltale sign of a rolling diamond particle.

So how do I run SiC on these without damaging the lap? Well, I took a risk. I cut a design that might have produced chipping (though it turns out it did not). If that had happened, the best coarse of action is to dress with the alumina sticks, clean the lap, then run a fairly tough stone next. If the cutting is running smoothly, then the chips produced are small enough to be insignificant. Most wash away with the water, some fall into the pores of the lap. In the most efficient processes, the lap material wears at such a rate that stability is achieved and no dressing is required over the life of the wheel. That can be a bit of a challenge with certain materials -- spent a lot of time in my career making that happen for SiC!


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 Post subject: Re: Adamas Sintered Lap Review
PostPosted: Mon Jan 27, 2020 4:43 pm 
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All Adamas diamond wheels use a reaction bonded metal alloy matrix which creates a layer of TiC on the surface of each bonded diamond grit to make the surface wetable with metal alloy. Thus, the possibility of a whole crystal falling out and scratching is close to zero. Some possibility of a piece of a bonded crystal breaking out exists, but with sufficient wheel speed and water drip, the particle would get washed off the wheel surface quickly. Slamming the stone into the wheel or rough dressing with silicon carbide sticks could cause that to occur.

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Last edited by thomas.adamas on Fri Jan 31, 2020 7:58 pm, edited 1 time in total.

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 Post subject: Re: Adamas Sintered Lap Review
PostPosted: Mon Jan 27, 2020 6:47 pm 
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Oh wow, that's really cool!

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 Post subject: Re: Adamas Sintered Lap Review
PostPosted: Tue Jan 28, 2020 9:14 am 
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@icurrier... I read your original post carefully three times. What a great review! Thanks much!!!


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 Post subject: Re: Adamas Sintered Lap Review
PostPosted: Wed Jan 29, 2020 4:46 pm 
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Another couple of updates:

2 more quartz stones (2 amethyst), two small indicolite tourmalines, and a chrome diopside (almost completely cut with the Twistor on that one) and I still do not need to dress these laps! Beautiful results!

I have a bit of traveling to do in the month of February, which will impact my cutting a bit! When I get back though, I'll have a few requests to cut. I'll keep tabs on the board, though!

If there are anymore products folks want a similar reviews for, just let me know. My arsenal also currently contains:

BATT -- 600 PCD, 3k PCD, 100k PCD
BA5T -- 60k PCD
Diamatrix (shamefully, it took me quite a few tries to get the hang of this one -- everyone else seemed to get it quickly! Got there eventually, though . . .)
Darkside (so easy to use -- but be careful with the pressure! One of my favorites for oxide polish)
Zinc+ - 8k
Ceramic -- 100k (rarely used anymore)
A Kingsley North 360 grit stolid steel -- basically just the odd bit of preforming

Somehow, I missed getting a Matrix (I'll fix that soon . . . ) and I have yet to try dual band laps, though I expect I will try that soon, too.


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