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 Post subject: Having difficulty with polishing sapphire
PostPosted: Tue Feb 27, 2018 4:21 am 
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Hey guys, after a few years of not having room to set up my machine I’m getting back into faceting.

I decided to leap straight into the deep end and tried cutting some sapphire. So far I’ve already ran into directional hardness, pitting, and complete unwillingness to take a polish.

My method started off with roughing in with 260 steel to carve the stone down, then I moved to 1600 for further refinement, then 3000 for the real cutting. Afterward I used 8k on zinc to move my facets into position and prepolish. Finally I’m using 100k powder on BATT but I’m getting tiny scratches and some pitting that refuses to polish out. *see attached picture, ignore the paper remains all over P1 on the pavilion, the scratches are on the P2-P3 series.

Best guess I have is to go back to the 8k and try to remove more material to get all the subsurface damage out. Any other ideas to try?

Thanks!


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File comment: Sapphire stone in progress
704202BE-99C3-4D60-8082-9D6F7A6FA613.jpeg
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 Post subject: Re: Having difficulty with polishing sapphire
PostPosted: Tue Feb 27, 2018 12:44 pm 
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Having difficulty with polishing sapphire

Unread postby Turkinolith » Tue Feb 27, 2

My method started off with roughing in with 260 steel to carve the stone down, then I moved to 1600 for further refinement, then 3000 for the real cutting

In my opinion based on your statement here lies your issue. Are these laps all steel? Are these what look to be scratches or possible leftover 260, 1600, 3000 surface damage. What does the surface present it self after the 8k zinc?

Many things to consider and without knowing exactly what your tools and methods are it is hard to identify the issue.

My sapphire methods are 260 standard crystallite lap if a 260 is needed, 600 sintered, 3k diamond batt lap wd-40, 13,14k to 100k on batts with wd-40 or 50k from 3k surface. 8k to 100k is a big leap especially if surface damage is still present after your 8k

I am not a fan of 8k on zinc, can be very aggressive even on the harder gemstones. That is me and others here use it with much success.

Greg

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 Post subject: Re: Having difficulty with polishing sapphire
PostPosted: Tue Feb 27, 2018 2:16 pm 
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Thanks for the reply!

My tools are:
All steel 260 lap,
1600 and 3000 are bonded diamond toppers placed upon a master lap.
My zinc lap is cast with 8k diastik.
BATT with 100k bort powder that I evenly lay out and use a piece of sapphire boule to gently roll into the surface.

As for the post 8k, I think you are right in it could be leftover surface damage.
Here is a picture I took after doing an initial pass with it on the pavilion. Now that I look at it again I'm noticing the scratches still hiding on the P3 tier.


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File comment: Just after 8k.
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 Post subject: Re: Having difficulty with polishing sapphire
PostPosted: Tue Feb 27, 2018 4:23 pm 
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Turkinolith wrote:
Thanks for the reply!

My tools are:
All steel 260 lap,
1600 and 3000 are bonded diamond toppers placed upon a master lap.
My zinc lap is cast with 8k diastik.
BATT with 100k bort powder that I evenly lay out and use a piece of sapphire boule to gently roll into the surface.

As for the post 8k, I think you are right in it could be leftover surface damage.
Here is a picture I took after doing an initial pass with it on the pavilion. Now that I look at it again I'm noticing the scratches still hiding on the P3 tier.


3000 toppers are notorious for leaving a very unfriendly surface. You might think about converting your 100k Batt to a 3k or 8k lap and getting a new Batt for 100k or just a new batt for 3k or 8k if your happy with the charge of 100k currently. Also you need not recharge with a piece of sapphire each time you reapply a fresh application of 100k to the lap. Using the sapphire to charge the lap is only necessary the first couple of initial charges to set the diamond into the lap surface, then just apply the fresh 100k with "yep I'm gonnna say it clean finger tip". Gearloose has a video on his site on the process of charging a new Batt.

I tell a lot beginners that stop by our store that if you think about "You can't polish a scratch with a flat surface lap" , maybe with a foredom or dremel bit but then your basically a carver not a faceter.

Greg

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 Post subject: Re: Having difficulty with polishing sapphire
PostPosted: Wed Feb 28, 2018 1:58 am 
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I recommend against using any lap coarser than 500 mesh diamond laps. You can create deep subsurface damage with very coarse laps such as the one you were using.

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 Post subject: Re: Having difficulty with polishing sapphire
PostPosted: Wed Feb 28, 2018 11:10 am 
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260 should only be used to cut bumps off that will be nowhere close to the finished surface 1600 as a next step would be fine BUT....only if you want to take alot more time then you need to with 600. 260 and not enough damage removal at 1600 to 3000....grand leap leaving a few grand canyons


Last edited by stairman on Wed Feb 28, 2018 3:05 pm, edited 1 time in total.

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 Post subject: Re: Having difficulty with polishing sapphire
PostPosted: Wed Feb 28, 2018 2:31 pm 
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Try placing a 600 mesh in your sequence if your needing to use the 260 mesh for removing excess material. The 260 should never be used to cut in facets as others have also implied here.
Greg

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 Post subject: Re: Having difficulty with polishing sapphire
PostPosted: Wed Feb 28, 2018 3:41 pm 
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I would skip those toppers. Do all your final cutting with a 600. Then prepolish with a heavy charge of 8000 on Batt, and final polish with 50,000 on Batt. Make sure your final polish on Batt is very dry, too much oil and you do get scratches. I use cutting oil, not WD-40.
Subsurface scratches from your roughing in lap is a myth.

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 Post subject: Re: Having difficulty with polishing sapphire
PostPosted: Thu Mar 01, 2018 2:32 am 
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I use the following sequence of laps and grits with good success. All with water drip, about 1-2 drops per second, laps running 700-900+ RPM. At that speed a good swift sweeping is required to prevent streaking/polish lines from the lap and diamond.

Roughing - 600 and 1200 on copper (1200 leaves orangepeel on some facets but it disappears very quickly at the 8k step)
Meets and pre-polish - 8k PCD on copper (outer band of my Redwing+)
Polish - 100k PCD on BA5T (centre of the Redwing+)

In general the 8k on copper cuts very fast, unless you've got a larger stone/facet but even then it's decent speed. I used to use 13k PCD on the copper band but found it was too slow for my liking.

The 100k PCD polish on BA5T is magic! Literally 5 seconds or less per facet will get out any 8k scuffs and put on a mirror finish.

I haven't used the cast zinc or Zinc+ on sapphire so can't say how that works.

Hope this helps

-Allan

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 Post subject: Re: Having difficulty with polishing sapphire
PostPosted: Thu Mar 01, 2018 11:46 am 
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I am with Gene on this - NO TOPPERS for anything finer than 260 (actually I own 0 toppers for faceting),
do most final cutting on 600 plated or sintered (might get away with 1200 sintered on small sapphires...).
Then I use 8000 on zinc (more aggressive than Batt), and 50k or 100k on BATT or BA5T for final polish.

Used to dislike cutting corundum because of the 1200 metal bonded orange peel.....

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 Post subject: Re: Having difficulty with polishing sapphire
PostPosted: Thu Mar 01, 2018 1:55 pm 
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I have never owned a topper, but I would think they should only be used for the coarser laps. The fine cutting is where you should put your money. A good solid steel or sintered lap makes sense here. A good 600 will allow you to place in all your facets very accurately and quickly, then an 8000 pre polish is all that is needed before your final polish.

For a round stone, I'll use a 220 to spin in a cone and girdle, this takes just a few minutes, then do all the cutting with a 600.

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 Post subject: Re: Having difficulty with polishing sapphire
PostPosted: Thu Mar 01, 2018 6:29 pm 
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Precision Gem wrote:
Subsurface scratches from your roughing in lap is a myth.

That is false.

Subsurface damage from a coarse roughing lap is FACT.
In the optical components industry, you have to lap with a series of smaller grits to remove the damage from the previous coarser grits to produce very low roughness and high transparency. I know because I sell diamond wheels and diamond compounds into that manufacturing sector.

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 Post subject: Re: Having difficulty with polishing sapphire
PostPosted: Fri Mar 02, 2018 10:47 am 
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If you are talking about deeper scratches from a coarse lap, yes I agree, but if you are referring to scratches below a smooth surface, then I think this is a myth in gemstones. I have cut thousands of stones and have never seen this. For all my stones I start out with laps that are pretty coarse, as I can’t afford to waste time roughing in a stone with a fine lap. I think that these fears of subsurface damage has caused new cutters to spend hours removing material, when they should spend minutes. Scratches in polish that are attributed to subsurface damage are scratches created during polishing. Just look at the direction of the scratch, and this will prove where they come from. Cut on one location of the lap, and polish on another so that scratch don’t align with each other and you will see that this is true.

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 Post subject: Re: Having difficulty with polishing sapphire
PostPosted: Fri Mar 02, 2018 4:15 pm 
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Is there a thread on the topic of Subsurface damage in Faceting Gemstones?
Define subsurface as it relates to faceting may be the answer. I say tomato and you say tomaahtoe really means the same.
I beleive in my experience in faceting that isn't in comparison to many on here who are much older (well not a lot as I am not that young anymore) and those who have cut ten of thousands, thousands or what ever amount of stones. Like in many types of fine high gloss finished items (ie) glass, cars, airplanes and such it is a progression of fine grits to finer polishes that acheive the end result. I too do not buy into the subsurface damage caused by a lower grit. But if your looking at in such a molecular level far beyound the faceting of a gemstone then I guess it can be called subsurface damage. I do not think that I place my dopped gemstone down onto the lap so hard, where that process might be considered creating a subsurface damage with a coarser lap.
As this relates to the new faceters who look to this board for some guidence and instruction in their beginning stages of faceting, they have a limited toolset and usually on the more economical side which means topper laps that is what they are dealing with. The Crystallite Standard lap is basically a topper on a aluminum backer for anywhere around $170.00 and up, where a topper backer combo can be had for $40-50. So how does this person find some satifaction in their quest to facet their first stones. Not blast them with all this you can't facet unless you throw all your crap away and get $700 sintered laps. I still use my first 600 solid lap that is an import $60 lap on Quartz, Topaz and many Garnets I like the feel of its thick heavy surface, I use my Crystallite sintered laps on corundum and spinel basically due to wear and tear maintence on my laps. I follow all with 3k on batt to other meshes on batts. Beginners should take some time to learn and understand the diamond industry as it relates to faceting " As not all diamond medium is created equal" my 3k might be Gene's 8k and possibly someone elses 2k.
Please all do not beat me up to bad in response to this!
Greg

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 Post subject: Re: Having difficulty with polishing sapphire
PostPosted: Fri Mar 02, 2018 5:29 pm 
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Precision Gem wrote:
If you are talking about deeper scratches from a coarse lap, yes I agree, but if you are referring to scratches below a smooth surface, then I think this is a myth in gemstones. I have cut thousands of stones and have never seen this. For all my stones I start out with laps that are pretty coarse, as I can’t afford to waste time roughing in a stone with a fine lap. I think that these fears of subsurface damage has caused new cutters to spend hours removing material, when they should spend minutes. Scratches in polish that are attributed to subsurface damage are scratches created during polishing. Just look at the direction of the scratch, and this will prove where they come from. Cut on one location of the lap, and polish on another so that scratch don’t align with each other and you will see that this is true.


Subsurface damage are not scratches, but rather a thin layer of brittle and ductile fracture caused by an abrasive grinding operation that is usually not apparent with a loupe. If you polish over that layer, pieces may break out and scratch in the direction of the polishing lap rotation.

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