High-quality, AMERICAN-MADE, flat-running, full 8-inch diameter, full 1/4-inch-thick master lap for calibration operations and to support topper laps.
What are the specs. Beiig that it can be used to calibrate a machine it should be flat within .0005 inches.
Thanks for dropping by, Ken.
Let’s look at what you said. It’s related to the issue of seeing faceting diagrams expressed to hundredths of a degree.
Most platens I’ve tested are true to about .0005 – across HALF the radius of an 8″ lap.
I can easily get a Facetron or an Ultra Tec to deflect by .001 if I lean on it while polishing – for instance, working a stubborn or larger Amethyst facet with CeO.
Most commercial laps are true within .001 – which is also about the amount of elastic deflection you’ll get with a commercial lap if you lean on it while polishing (as above).
And, varying the amount of polish on a polishing lap will cause the depth to vary by easily as much as the .0005 you’re talking about.
While a really fastidious person might be able to get their instrument calibrated to within .0005, unless they’re using custom-made laps the degree of precision is going to disappear the second they put that next lap on it – or the next time they change the charge on the lap. And, absolutely, the next time they score the lap or decontaminate it, they’re going to shift the calibration by more than that .0005.
So, .0005 is an extravagant level of precision really moot for all practical purposes – to include competition cutting.
If you really want a lap with a level of precision past all practical use, you aren’t going to get a metal one for under $50. You can’t use rolled stock to produce it (due to internal strain). And, you can’t just turn one on a lathe. You’re going to have to pay for high-precision blanchard grinding to flatten it properly. You MIGHT be able to create a DIY lap that flat by finding a high-quality piece of half-inch plate glass and drilling your own arbor hole in the center with a diamond core drill. That’s likely to have the flatness you’re talking about, but you’ll have to handle it pretty carefully.
A short and straight answer to the “what’s the tolerance” question is (according to our USA-based manufacturer):
The typical precision of the laps we’re offering for under $50 is .0015, and they do come with a satisfaction guarantee that if you manage to get one that’s not that good, you can return it for replacement or refund.
This level of precision is plenty, even for a competition cutter, given that it’s more accurate than the typical commercial laps a faceter is going to be using.
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