I am interested to know more about the machanism by which the diamond bonds to the different types of lap.
I expect porosity has a role to play as pores of the right size should be able to trap the diamond, increasing the surface area on each particle available for covalent (I think, I'm a little rusty on my Chem terms) of the diamond to the metal.
The alternative is the diamond pushes into the metal and is traped like a stone set in a gypsie setting, or the diamond is in solution and slurry polishes.
On zinc laps, diamond definitely incorporated well in the surface of the lap. It doesn't scrub off with a brass brush or solvol. I know because the lap continues to cut stone after stone with just the addition of lubrivcant.
Regards
Gordon.
Anonymous wrote: I am interested to know more about the machanism by which the diamond bonds to the different types of lap. I expect porosity has a role to play as pores of the right size should be able to trap the diamond, increasing the surface area on each particle available for covalent (I think, I'm a little rusty on my Chem terms) of the diamond to the metal. The alternative is the diamond pushes into the metal and is traped like a stone set in a gypsie setting, or the diamond is in solution and slurry polishes. On zinc laps, diamond definitely incorporated well in the surface of the lap. It doesn't scrub off with a brass brush or solvol. I know because the lap continues to cut stone after stone with just the addition of lubrivcant. Regards Gordon. Yes, I think your heading in the right direction Gordon. I agree there is no doubt that the diamond would embed in the softer metal and continue to cut with additional lubricant. And trapping of diamond in pores may well be a benefit. Most gem cutters are well aware not to use variant grades of diamond grits on the same tin / metal laps as the result will be contamination. This proves that diamond can embed into the metal surface. And most likely diamond will also embed into a plexiglas lap also. The question is this long term build up of diamond and gem dust into the lap really beneficial to polishing or not? I've noticed on copper and tin laps that I've used and those of other faceters, there is a tendency see grooving on the disc. Very much like grooves on a vinyl record. While on a record the grooves are designed to drag the stylus in, the opposite occurs on the lap. You would have noticed that by placing the faceted side on the metal lap without holding it, the drag of the stone and the quill will lead to the outer edge and would slide entirely off if not held. The surface area of plexiglas is a lot smoother than the surface metal laps when used and cared for. I've noticed if I keep that surface as smooth as possible from scratches and grooving and get the flat of the facet dead onto the flat of the surface of the lap there is hardly no drag or resistance (unlike a metal lap). Actually, I could walk away for 5 minutes without holding the quill and it would continue to remain in one spot, as this is the point of least resistance. Exactly the same principle of using anti skating on a quality turntable, you can adjust the counterweight so there is minimal resistance and find the sweet spot where the stylus is creating the least resistance without digging into the groove too much but continue to play. Of course you could make the anti skate so light that needle just floats on the groove without it moving ( but what would be the point, as you would hear the same music repeat). My theory is (and it's just a theory) - I want to float as much diamond between the surface of the facet and the lap as possible. And because my aim is not to embed the diamond in the lap, rather keep the diamond swirling under that facet. Which still means you still move that quill side to side, but your only doing that to keep the diamond continually between the lap and the facet you wish to polish. If you just left the quill in one position all the time it would squeeze the diamond and extender to the outer edges of the facet. That may explain what you mentioned about rounding. Although rounded facets applies more to the use of cerium oxide rather than the use of diamond. Much on what has been discussed, should really be put to the test and backed by evidence, rather than heresay or marketing. If I personally find that the plexiglas is faster, easier to clean, a healthier option, and does as good a job on polishing than a tin lap, there will be no way I'll bother to use a metal lap again. Not having to clean the black residues left behind is already a bonus, the smell of WD40 is not that pleasant. Regards Cliff
Yes, I think your heading in the right direction Gordon. I agree there is no doubt that the diamond would embed in the softer metal and continue to cut with additional lubricant. And trapping of diamond in pores may well be a benefit. Most gem cutters are well aware not to use variant grades of diamond grits on the same tin / metal laps as the result will be contamination. This proves that diamond can embed into the metal surface. And most likely diamond will also embed into a plexiglas lap also. The question is this long term build up of diamond and gem dust into the lap really beneficial to polishing or not? I've noticed on copper and tin laps that I've used and those of other faceters, there is a tendency see grooving on the disc. Very much like grooves on a vinyl record. While on a record the grooves are designed to drag the stylus in, the opposite occurs on the lap. You would have noticed that by placing the faceted side on the metal lap without holding it, the drag of the stone and the quill will lead to the outer edge and would slide entirely off if not held. The surface area of plexiglas is a lot smoother than the surface metal laps when used and cared for. I've noticed if I keep that surface as smooth as possible from scratches and grooving and get the flat of the facet dead onto the flat of the surface of the lap there is hardly no drag or resistance (unlike a metal lap). Actually, I could walk away for 5 minutes without holding the quill and it would continue to remain in one spot, as this is the point of least resistance. Exactly the same principle of using anti skating on a quality turntable, you can adjust the counterweight so there is minimal resistance and find the sweet spot where the stylus is creating the least resistance without digging into the groove too much but continue to play. Of course you could make the anti skate so light that needle just floats on the groove without it moving ( but what would be the point, as you would hear the same music repeat). My theory is (and it's just a theory) - I want to float as much diamond between the surface of the facet and the lap as possible. And because my aim is not to embed the diamond in the lap, rather keep the diamond swirling under that facet. Which still means you still move that quill side to side, but your only doing that to keep the diamond continually between the lap and the facet you wish to polish. If you just left the quill in one position all the time it would squeeze the diamond and extender to the outer edges of the facet. That may explain what you mentioned about rounding. Although rounded facets applies more to the use of cerium oxide rather than the use of diamond. Much on what has been discussed, should really be put to the test and backed by evidence, rather than heresay or marketing. If I personally find that the plexiglas is faster, easier to clean, a healthier option, and does as good a job on polishing than a tin lap, there will be no way I'll bother to use a metal lap again. Not having to clean the black residues left behind is already a bonus, the smell of WD40 is not that pleasant. Regards Cliff
The other component of "Special alloy" I am not prepared to reveal, since I believe that the maker of the lap is entitled to retain a competitive edge as long as possible, having been enterprising enough to pick up the idea of using the material. Suffice it to say that it is another safe material.
I was not hooked by any marketing hype - as a scientist I made my choice after being asked to trial the material and report my findings as an amateur cutter with a lengthy experience of other polishing media. I tested the lap by polishing a wide variety of natural stones, in a range of different sizes. I did not do synthetics, simply because I never cut them unless forced to for a competition and I have been out of competition for quite a few years now. Maybe some time I will feel the urge again. When I was cutting them, however, the only one that ever gave me any trouble with polish was a diabolical dark blue spinel that I encountered in my very early days of cutting.
So the gem is completed. I can say the experiment by using a perspex lap exceeded all expectations. I will be getting other very good faceters to closely inspect whether rounding of facets is a issue, but under a 10X Belomo loupe I cannot see any difference, in fact they appear sharper. Polishing time had also been a factor as the pre polish and final polish were a quicker than on tin. I can also say that the diamond will embed into the perspex. I felt it would, but I can conclusively confirm it retains diamond, but not for that long. As for tin laps or other special alloy laps ( that I suspect are H.R laps), that CZ had polished easily and better for me than on tin. I will test various other gems (both hard and soft) to make other comparisons. If that proves as good as the polish on CZ, the tin lap will be gathering dust.
Regards Cliff
Hi Cliff,
Thanks for the update. If the concensus is no rounding, it would seem rounding of facet edges is a function of how much slurry you put on yhe lap rather than the type of lap.
I'll give it a go if I can get a perspex lap that is true. The couple I have need trueing, the dial indicator wobbles when I use them.
I started using Bob Boddington's advice, to put a minute amount of diamond on the lap with a drop of extender, smeer it over tje lap then wipe it off and polish with the residue. But now spray a minute amount on a makeup removal pad with a few drops of lubricant on it and continuously wipe off the swarf with said makeup removal pad as polishing progresses. This minimises the risk of stray diamond finding its way to precision ground surfaces and bearings. It works for me as I use relatively high polishing speeds.
Gordon
Hello all.
I read this thread with interest as someone who loves DIY and tricks like this. Of course perspex laps have been around for a while but I had never tried them. After reading this thread, I slapped an old blank CD onto a master lap and did some testing of my own.
This comment by the OP in particular had me curious/skeptical
>you could get a pretty high polish on a 2.5 micron 4000 grit paste.
So I tried polishing a flat spot on some local labradorite with 600 grit diamond topper, then onto 8k on perspex. I now agree that the result of this pre-polish could easily pass as commercial "final" polish. Noticeably smoother than the pre-polish I'm used to from 8k on copper.
I can't weight in on rounding because my tests were done hand-held but I did notice that even with an excess of paste and a fair amount of pressure, no scratches. (maybe I got rounding instead).
Finishing off with 50k on another CD = mirror finish, to the point where I had trouble focusing on the facet with my 10x.
Anyway, I'll certainly give this a try on a proper gem and encourage other to try for themselves. thanks!
Hi Rej, I'm on to cutting a Citrine, and the pre polish 2.5 micron 4000 diamond paste worked great after using a worn 600 grit diamond disc. Then I went on to a 1.0 14,000 grit and that really took it up to commercial grade polish. I agree that a 8000 grit would have a similar effect. Had a few light scratches under the loupe, so I used the synth 50,000 diamond paste but that was slow. So I just moved on to cerium. And no doubt cerium is faster than the synth pastes. But you need to take care as it can really cut into quartz based gems a lot faster than synth diamond paste on perspex. On the CZ I used 50,000 diamond grit with oil and that worked well on that gem. Now I'm cutting the crown on the Citrine I may go back to the 50,000 diamond grit with oil. The other thing is the perspex disc that I only use with cerium has some cerium embedded in it after a bit of usage. I'm going to test if the trace cerium that is embedded in the perspex polishes without adding additional cerium. I have a sneaking feeling that it will do a fantastic final polish. As it should be no different in behaviour than a ultra lap with cerium. I'm still waiting on a couple of chaps from my gem club to return from holidays and evaluate the edges of the facets of the last gem I cut, to see if there is rounding. I really doubt if they would. I know a lot of gem cutters on the forum generally like to cut for comps, which means cutting the same design time and time again to get the elusive 100 points. I take the same approach to gem cutting as I do to my music. I see guys playing the same three same chords for 40 years, and yep they may be the best playing three chords better than most. But what makes the best musicians are those who are willing to play all styles and techniques through practice and experimenting day after day. I don't want to be one of those facetors who only wants to cut a perfect round brilliant. I want to be more like a John Bailey or Jeff Graham of the faceting world. Glad to see that your also testing the waters. There is so much yet to learn and improve on.
Cliff,
I was interested to hear that cerium has embedded into your perspex lap. I'll be interested in the results of your test of that lap with water and no additional cerium oxide.
Pushing the boundaries through experimenting and informing others of the results are high on the list of activities that advance our understanding and technical expertise. Keep it up.
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