Polishing Quartz with diamond

[Faceting Frank]

Going to enter some stones in the competition at the Gemboree 2021 which is held in Hobart Show Grounds. This will be my first time entering this annual comp. its organised by the “Australian Federation of lapidary and Allied Crafts Associations” (Wow what a title).

The open faceting section is in three parts and seven stones in total, there is a lot of Quartz in it, which I’m not a fan of as far as competition stones is concerned. I polish it with Cerium Oxide on Lucite, which usually works ok. But sometimes it starts to play up and put faint scratches in. Normally not a problem but for comp. stones no good and they have to be polished out. Thus loosing meet points and it becomes a total pain.

Polishing with diamond I go from a worn 1200 bonded to a 3000 batt lap, to 60k batt. With CZ, corundum etc. the 3000 will produce a brilliant pre-polish and I don’t even bother turning the machine on with the 60k. Just wiping the stone across a stationary lap.
The 3000 doesn’t produce anything like the same finish with Quartz and it’s taking ages with the 60k. I was just wondering those of you that polish Quartz with diamond, what grit do you use as a pre-polish.
Thanks.

[Pro-oz]

I am still very much a beginner Frank, and will take all the advice I can get. At the moment going from a 3000 diamond lap to polish on tin with 60k and not having any problems, polishes pretty quick. I often use your idea and polish on a stationary lap, and often finish off on the stationary lap and it does work.
I think my polishing is pretty good, never have had a problem with quartz. One day may enter a comp just to see were I'm at.

Cheers
Prooz

[MakkyBrown]

For quartz I use 100k on tin quite aggressive fast lap heavyish hand this might not be good for comp stone as the edges round slightly. I'd be temped to try a 8k prepolish of tin(or your batt but the batt is a lot harder) then 100k or 60k polish. I go to the 100k from 3k but it's not a 3k prepolish it more a frosted finish from a relatively aggressive 3k cut and I don't recommend doing what I do. I use a generous amount of 3k/wax mix on brass and it cuts pretty fast but gives a very even finish without clipping or scratches.

[Rusted]

I am beginning to think Quartz polishing problems come down to sub surface damage.

Try giving coarse laps a complete miss and just grind with finer grits. It takes longer but I think the results are much better, especially when you can go to diamond and get a really good hassle free finish.

[Bucket]

Funnily enough, so far I've never had a problem polishing quartz, I was taught using 50k diamond spray and one of those thin plastic laps that are impregnated with cerium oxide. I now use a thin mix of cerium on a pewter lap (made by one of our members). Pre polish is either a very worn bonded 1200 or 3k bonded lap, both seem to work well. I'd agree with you Rusted about the really aggressive laps, I think you're better off keeping above 320. I do use a 180 to rough down some really badly shaped stuff, but that's just pre shaping if you like.

[Faceting Frank]

Going to go from 3,000 to 14,000 to 60,000 grits. Got a spare batt lap, so no problem having a dedicated 14,000 gritter. 3,000 to 60,000 is to big a jump for quartz because it wont produce the same finish on the 3,000 grit like CZ etc.

I've always used cerium oxide to polish quartz, but not getting the standard of finish I want for some reason. I have heard that some quartz rough can be a problem.

[FlashGP]

Hi Frank,

I started faceting quartz with diamond, moving from 1200 to 8000 on zinc to 60k diamonf on a Darkside until I ran into Kingsgate quartz that may have been twinned and I had trouble getting a polish. 

Brian at Gem Cuts put me onto the lightning laps and I now polish with zirconia on an 0.3micron Linde A lap using water and finish with 100k diamond on a Batt or Darkside.

I have since found cutting with water to be the secret, quartz hates oil and loves water as a coolant.  For example quartz is happier being cut with water dripped onto my zinc lap or a copper lap with 8k diamond embedded in the surface.

Regards
Gordon

[Faceting Frank]

Hi Gordon,
I've used a Darkside lap and Zirconia to polish quartz. Very aggressive but will produce a good polish as will cerium oxide on Lucite, both using water.

Getting the pre-polish to a standard that allows me to polish by moving the lap by hand is a big advantage as far as comp. stones is concerned. It gives me better control and allows me to bend facets slightly with the mast screw and cheater to finish off meet points. Another advantage of a stationary lap is it will not put scratches in the facet unless there is some contaminant on it. Like a grain of 3000 grit, only other thing is too much diamond will put tiny ruts in the facet.

[FlashGP]

Hi Frank,

Thanks for your earlier tip regarding the stationary polishing lap.

I have used it to effect, and itt saved me melting down a good lap in disgust.  I have had to resurface a couple of polishing laps after the facet sucked the surface of the lap off like peeling an orange.  I put it down to the suction between a glay facet and a flat lap using 100k diamond, and too much lap speed.

Syationary lap means that I eliminate this problem as the lap starts to get a polished finish.

Regards
Gordon

[Dihusky]

Cut a fair bit of quartz and always finish with diamond, I've tried cerium on lucite, have a Darkside plus a couple of Lightnings none of these have ever worked for me. I think a lot may be due to not knowing what the previous owner used on them as most came with the VJ. When the VJ moved on we held onto the laps as we didn't want to pass on problems.

My system for quartz, depending on the size of the stone, is 1200 sintered bronze, 3k on copper if the facets are big then 8k on copper, or straight to the 8k copper for small facets, cleaning regularly. I use Baby oil and have never had a problem though have used water in the past and it worked well.

Final polish is 50k on Tin, my Tin lap has been indented with a linear knurling tool and this speeds up polishing significantly. Often push facets by hand wiping as the Tin lap can polish so fast it can be easy to go too far. The other benefit of knurling is the lap doesn't squeak on the table.

I have also used Tony F's lube powder with 60k which also worked well. With both systems I use a miniscule amount of Diamond, plus by now there's plenty embedded in the Tin until I redress the lap.

[Pro-oz]

Hi Dihusky, have just had my tin lap refaced, and have heard little bits and pieces about knurling a tin lap. Is this tool rederly available?
Would like to know a little more about the knurling if you could.

Cheers
Prooz

[MakkyBrown]

I knurl my tin lap aswell, working the tool slowly across the lap surface with the machine running. I think it is a 1mm pitch straight knurling tool, I'll have a look tomorrow when I get home. You can buy on ebay.
MB

[FlashGP]

Hi Prooz,

The knurling tools I have seen are designed to go on the tool post of a lathe and are for putting the cross hatche patterm you see on handles of tools like socket wrenches.  From memory they ones I say cost $70 to $100.

Knurling provides channels to allow air to get to the facet breaking up the surface tension or vacumme at the boundary between the lap and surface being polished.  It can really be a problem for big facets.

I have tended to avoid it and scoring for fear of allowing swarf and polish build up in ghe channels and scratch the fscet, hence why Dihusky only needs minute amounts of polish.

I have been interested in knurling as a way to stop large facets damaging or being damaged by the polishing lap.  I ran into this when polishing a 4 x 6cm facer on a piece of rainbow flourite, the surface tension/vaccume kept tearing tiny crystals from the surface of the flourite facet.  I solved it by using the peaks on a new 50k lightning lap.  The peaks in the surface did the polishing and the valleys stopped the vacumme building up.  Same principal as knurling.

Regards Flash

Re

[FlashGP]

MB, hadnt thought of EBay.  I had been looking in the local machine tool supplier's catalog.

[Pro-oz]

Thank you for the reply, MB and FlashGP I had looked at knurling tools on ebay some time ago. I'll have a think about it, bit hard to do on my newly faced lap haha. Thanks FlashGP now I understand a bit more about it, hadn't thought about it the way you put it, thank you.

I will end up knurling if it's go to make it better.

Cheers.