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Posted in response to Re: Re: Scratching Laps from Carter Arnold on July 18, 2008 at 08:15:05:

Re: Re: Re: Scratching Laps

Hi again Carter,

I asked what you were cutting and how much time you had on your laps that are scratching to try and get an idea if they are simply worn out. When electrobonded laps get to a certain stage of wear they start scratching, and if they are truly worn out there isn't much you can do to remedy that except replace them.

Never having used one, I'm not familiar with the Lapcraft laps, but I assume they are electrobonded laps. However, from the amount of use you describe I think your scratching issue is more likely due to contamination than your laps being worn out.

First off, when you are cutting on water lubricated laps, you really can't get too much water on the lap. You need to have a good flow of water to help transport the cutting swarf away as quickly as possible. I know it is a pain to have to keep refilling the water tank when you run the water heavy. I help minimize trips to the faucet while I am cutting by keeping several gallon jugs at hand so when I do get up to refill, I refill all the jugs.

If your scratches are coming from contamination, there are several possible sources including chunks of diamond bort from a coarser lap that are now embedded in your 600 or 1200, chunks of previously faceted material harder than the material you are currently cutting that have contaminated your lap, or chunks of the material you are currently cutting.

When you change from a coarser to a finer cutting lap, there is always the possibility that you will transport contaminating material in the process that can cause problems downstream. Are you cleaning the stone thoroughly between laps? You can also suffer contamination from swarf that splatters on your dop, faceting head, the splash rim, tank hose, etc. It dries, then you brush against it after you have installed the finer lap, and bingo you have a problem.

If you wipe your stone while cutting with a rag or paper towels, those are also an obvious potential source of contamination. How do you store your laps? If you use the cardboard boxes they came in, or lap containers, be sure your are returning each lap to its proper container. Throwing a 1200 or 3000 lap in a 100 box is a good way to contaminate it...

Another possible source of contaminating particles is your water supply. I once mangled the polish on the final facet of a comp stone I spent about 80 hours cutting with a grain of sand or a fleck of some other mineral deposit in the water pipe that made its way from the faucet into my drip tank and out onto the lap... . This happened right after I had refilled the jug - if only I had let it stand for 10 minutes before refilling the drip tank. Now I use a filter between the drip tank and the lap...

Some materials are notorious for shedding particles and making their own scratches. I once had a piece of San Carlos peridot with "lily pad" inclusions that are characteristic of this material. It was very trying to polish, because the inclusions would open and shed particles, next thing you knew, big scratch...

Given the low drip rate you described using, your laps may be choked with swarf. Clean them by spraying sloppy wet with WD-40, let that sit for about 15 minutes, then scrub the lap with a toothbrush or a brass brush, which is what I like to use. Rinse and repeat that cycle about 3 times. You will probably be amazed at how black and yucky the WD-40 gets with removed swarf as you do this.

Then try your luck again and see if you still have scratching issues. Good luck and let us know.

From Bob Keller - July 22, 2008 at 12:49:02

Message: 66770

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