May 10, 2016 at 4:56 am #2627
i am trying to cut my first saphire (for the second time). i am having problems and am not sure what to do next. i am wondering if some of you experienced faceters could give me advice about laps to use. i have cut approximately 45 stones and am very happy with my results but my first saphire is giving me great trouble. it does not seem to matter what i use to cut it with i am getting an unbelievably pitted surface. i have tried all of my usual laps/ sequences. my finely worn 1200 topper gives a horribly pitted surface as does my well worn 3000 topper. i tried my nubond 600 and it seems to give a better pre-polish but struggles to get rid of all of the pits. i have talked to a few faceters here with more experience than i and have been told to not go too fine on the laps (i.e. stay away from the 1200 and 3000) and just go to Nubond 600 after a 600 grind then go straight to the polish. i must admit i have not gone to the polish yet as some of the pits are still present and it doesnt seem right to me. any advice would be welcome and, in particular i am interested in which laps you are using for saphire .May 10, 2016 at 2:32 pm #2628
Corundum is notorious for pitting with 1200-3K plated laps, and the fact that your laps are worn doesn’t help. I’ve always had good results on BATT, roughing with 325 grit if needed, else 600, fine cut with 1200, prepolish with 3K, then polish with 50K. More recently I’ve used 100K Blakstik on Diamatrix for polish.
I recently got a set (600-1200-3K) of sintered laps, but haven’t yet cut any corundum with them.May 12, 2016 at 2:58 am #2633
Tom and Alan, thank you both very much for your replies and advice.
i have been trying to do the 600 topper followed by the 600 Nubond. . it seems to be taking forever for the nubond 600 to get rid of the pits – in fact i am still trying.
i have been wondering if i should obtain a nubond 325 and use that instead of the topper 600…… but for now i will persevere. if i continue to struggle then i may have to change to another approach like batt lapp with loose grit as suggested by AlanJune 7, 2017 at 11:35 pm #3279
hi i see these names popped around of laps—what– i have been cutting for long time and am posting answers/comments on all subjects. oh yes the sapphire is a problem, what people are usually not aware of is its plains. topaz has one plain and one must tilt the stone to not put any facet on directly parallel to it as it peals or pits. the same is with the sapphire only it has 3 growth plains if all 3 are at same angle you would have a perfect 6 sided crystal but the very rarely are at the same angle thats why the weird shaped crystals. i’ve cabbed one of the largest cabbed sapphires and rubies that were 10 lb+ while working for crystalite and those plains were very noticeable and really had to work to get the polish. i’ve found if your lucky enough to get around those growth plains you can polish with 50,000 grit if quality stone, but have found that its best to polish with 8000 for final on the trouble ones. just a thought to try. mike zinski email@example.com p.s. the man made sapphire your not likely to have that problem as they do not have those growth plainsAugust 18, 2019 at 10:43 pm #5560
recently members of my club and students have been coming up with small montana sapphires they have collected on road trips there. and ya we see a lot of them have what looks like pitting. we use either a 1200 or 3000 metal bond((plated) diamond disc that some call toppers which we all prefer here and much cheaper from china. when we see a pitter facet we cut it not all the way in to the mark and instead polish it in, just take a little longer. we use a tin lap very slow speed with diamond powder and very slow drip of water to make a muddy slur– no oils or pastes. and we have very good success. as to the sintered lap some are so proud of i wouldn’t own one. they are high priced and a waist of money. they are diamond grit mixed with metal powder then fused together to a lap. the diamond is not all on the surface so your not getting any use out of it and as your stone starts wearing away the metal, like in a saw blade, the surface changes. no thanks from 1968-1977 i worked for crystalite making/plating those metal bonded lap and you have a mass of diamond surface. the china ones have even more diamond than those made here. a for sintered ya they last 20 yrs maybe but a poor cutting surface. i have my crystalite’s from then, from 1968 an still use them just fine and the coarse ones can be sharpened up just like a saw blade. firstname.lastname@example.orgAugust 28, 2019 at 4:59 pm #5581
I cut all my sapphires from Montana first rough out with 260 next prepolish 600 next 3000 polish on batt next polish on matrix with 60,000 finish with 100,000 on matrix all polish from gear loose no problems with pits ever stop all cutting after 600 lap.September 1, 2019 at 1:49 pm #5584
600-3k or8k- polish works great. Just transferred a small Montana sapphire last night.
When you are roughing the stone just stay away from anything in the 1200 range and you’ll be fineSeptember 10, 2019 at 2:53 am #5598
I just cut my first corrundum. It was a lavender sapphire from Sri Lanka. I did it with a 600 Crystallite for roughing.
Then I switched to 3k pandamonium on a zinc plus lap. I use 3k and 8k to cut. These grits are not just a prepolish for me.
I found I did experience pitting with my 3k, especially with heavier pressure. Lighter pressure didn’t result in as much pitting.
My stone was only about 1.2cts when I started so not much wiggle room. I moved to 60k on a diamatrix despite the pitting so I wouldn’t wreck my stone trying to cut the pits out. I used 60k to cut the pits out. It took forever.
In retrospect I should have cut on my 8k Batt lap instead of 3k on zinc. I believe it would have resulted in less pitting.
I still have a few more Sri Lanka sapphires and longido rubies to do. I’ll update as I cut them if you’d like.
Here’s a photo of the lavender sapphire. Bear in mind my picture taking skills are awful.
Attachments:You must be logged in to view attached files.September 10, 2019 at 2:57 am #5600
I just realized this is a revived thread from 2016. You are probably not wondering about this anymore lol!September 10, 2019 at 1:04 pm #5601
Nice looking sapphire.
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