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 Post subject: Lap questions from a beginner hoping to cut mainly sunstone
PostPosted: Sat May 13, 2023 5:00 am 
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I've got a new machine, and am in the process of buying laps.

I'd love to cut a lot of sunstones, but also be open to cut quartz, garnets, maybe sapphires or other stones local to in and around my state.

Question 1.
What type of 600 grit lap will serve my needs if I'm planning on going from 340 -> 600 -> 3k -> 50k?

I currently have a master lap, and two BATTs-- one for pre-polish (3k) and the other for polish (50k).
So I think I need to buy a ~340g for rough cutting, and a 600g for cutting/fine-cutting.
I think a topper lap will be fine for the 340g, but I'm really unsure what kind of lap would be 'ok' for the 600g, given I'm going straight from 600 into pre-polish. I know the sintered is recommended, but I'm not sure I can afford one right now. I've seen people say a 600 topper works just fine, and others say it doesn't. I'm looking for some advice on what type of 600g lap to get, given I'm going straight into a 3k pre-polish.

Question 2.
I've read that using a particular lap with a particular type of stone can make that lap unusable for other stone types, since the grit from the last stone will be in the lap.

Is there somewhere I can read more about this issue? Can certain stone types/hardnesses be used on the same lap? Is there any way to clean away left behind stone grit?

It's daunting to hear I may need to buy multiple laps for individual types of stones, but if I must so be it.


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 Post subject: Re: Lap questions from a beginner hoping to cut mainly sunst
PostPosted: Sat May 13, 2023 1:25 pm 
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Location: San Marcos, CA
Q:1
Issues with 600 toppers range by manufacturer. My general rule is you get what you pay for. We can both go on ebay to say and buy a 16$ and a 28$ lap and get the same results, differing results, or extreme crappy results. These laps are typically mass produced and the diamond used can have varying median values 600+- in mesh and stray particles that cause excessively deep scratching. Buy your cutting topper and a 600, use a sacrificial piece of rough (quartz, synthetic corundum) cut a surface with the cutter grit you buy, inspect the surface, a decent lap will leave a consistent looking surface. Follow it with the 600 and inspect it with the same scrutiny. Then with the 3k Batt. If you find your having to apply extreme pressure or amount of time to get a decent pre-polish then better laps may be needed. This is just a simple scenario, as learning to read your surface is gained by experience rather than me telling you to just do it. The 3k diamond your using, the rough your using, all play parts in what your 50k Batt results are going to be. It is easier to say to you just get cutting and start gaining the knowledge that works best for you. Remembering that most stones your going to will have far more smaller facets than large, so one bad scratch on a facet is what your trying to avoid. Hope this helps more than possibly adding more confusion.
In the end The Standard 600 lap by Crystallite(AbrasiveTech) is more consistent but more pricey.

Q:2 NONSENSE STOP LISTENING TO IT.
You control the fate of your laps.
Many gemstone properties may vary on how they react to your cutting and polishing technics, but to say that it is caused by I just cut a different gem species is the cause. Take care of your laps learn how to clean them after use, storing them, etc. I never think when I pull out a lap to cut a gem, oh wait I just put a table surface on a tanzanite so I can't use this lap on this or that. Nonsense.

Sunstone is a very easy gem to cut.
You can just use you 600 as the cutting lap, unless you need to remove a large amount of material, but not likely.
Pre-polish with WD40 on your 3k and follow up with you 50k. Again assuming your rough is not heavily fractured or having surface reaching inclusions that wd40 is going to penetrate.

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 Post subject: Re: Lap questions from a beginner hoping to cut mainly sunst
PostPosted: Sat May 13, 2023 7:40 pm 
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@glhays

Q1. That's very helpful, clarifying information. I'm going to look into one of those 'The Standard' laps, though I'm feeling less afraid of dealing with a topper if I need to.

Q2. Thanks for debunking the idea that one stone species can taint a lap for other species. I'm going to look more into what I need to do to maintain clean laps.

Also thanks for the advice for cutting sunstone. If a 600 is usually all it'll take for my cutting phase, I'm almost tempted to go for a nice sintered. Maybe someday soon.


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 Post subject: Re: Lap questions from a beginner hoping to cut mainly sunst
PostPosted: Thu May 18, 2023 1:09 pm 
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gemjohnson wrote:
Question 1.
What type of 600 grit lap will serve my needs if I'm planning on going from 340 -> 600 -> 3k -> 50k?


Honestly, I'd recommend a 260-grit topper lap, not a 340-grit. You're using the 600-grit lap to clean up the remaining subsurface damage and get your meetpoints accurate, so it's ok to use a coarser grit and make things faster. Sunstone doesn't typically have enough cleavage separation for a 260-grit to be problematic.

For the 600-grit itself, the two most common recommendations are high-quality sintered laps, or a BATT lap with 600-grit Pandimonium. I personally have tried both and prefer the BATT option, as I can apply a fresh charge to make cutting faster OR I can use an "older" charge to have a much finer finish without sacrificing speed.

gemjohnson wrote:
Question 2.
I've read that using a particular lap with a particular type of stone can make that lap unusable for other stone types, since the grit from the last stone will be in the lap.


This is almost entirely BS. Rarely, some types of garnet will be "self-fouling", which means that they'll crumble a bit and then scratch themselves, but this is extremely uncommon and typically can be avoided with more meticulous subsurface damage removal at every step. Some synthetics will also do this, like smelter-byproduct zincite which can have flakes of zinc metal, or some types of hydrothermal Paraiba-colour beryl that have literal crystals of copper as inclusions. But again, wiping down your lap should be enough to solve this problem (if it ever occurs).


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 Post subject: Re: Lap questions from a beginner hoping to cut mainly sunst
PostPosted: Thu May 18, 2023 3:47 pm 
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Only gem I have ever had foul a lap was a green metamict zircon - structure was so damaged be radioactive decay that it was extremely friable - edges just kept crumbling, and particles buried themselves in my typemetal lap. A Batt may be enough harder to avoid the issue.

On the polishing side... Some sunstones don't get along with metal laps/diamond regardless of lap speed, wetness, pressure, or polishing direction. Just finished one of those - no matter what I did, polishing on some surfaces with 50K/metal would cause deep fractures along the facet - not on a cleavage. Finally went old-school and polished with cerium oxide on acrylic. Same on a Darkside also did well. Most of the time you are fine with metal/diamond, but when a strange one comes up, you are glad to have more tools in your drawer.

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 Post subject: Re: Lap questions from a beginner hoping to cut mainly sunst
PostPosted: Wed Jun 28, 2023 10:57 am 
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If you are new look at splitting your lap to prepolish on the outside and polish on the inside. Take a sharp tool anything will do. Scribe a line. The you can go from prepolish, clean stone, and polish. If you have scratches jump back to prepolish. No changing of laps, finding the height, or missing an index.


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