This video explains how and why to score your laps (or not). Done properly – and in the right circumstances – scoring your lap can make polishing faster and more trouble-free. Done improperly – or in the wrong circumstances – scoring will just ruin your laps or cause you no end of grief.
The video above talks about scoring a composite lap, and using either carborundum sandpaper or a bit of hacksaw blade. These methods are probably the best for the composite laps – everything from Phenolic to Corian – even to Matrix and Diamatrix laps (the sandpaper for these latter ones).
However, both the sanding paper and the hacksaw are not best for scoring laps like copper, zinc, tin, or even the high-tech ones like BATT or BA5T.
I personally score my BA5T, and here’s how:
Buy a small, stainless steel wire brush (not much bigger than a toothbrush). Keep it CLEAN, and free from contaminants. I keep mine in a Ziploc baggie.
Strip all old polish and swarf from the lap, using whatever solvents you prefer. I may use WD-40, Isopropyl Alcohol, etc – and vigorous scrubbing with a paper towel. Then, with the lap mounted on the platen, I press the bristles of the brush firmly against the surface and drag outward from the spindle. I turn the lap a fraction of a turn and repeat – until the entire surface has a shiny, brushed finish. The lap should NOT feel like it has deep scratches in it. It should just feel like there’s more friction than before you began – like ANY wire-brushed-finished piece of metal.
After this process, I scrub the lap again, and then charge it and polish a chunk of quartz to smooth out any bits of metal that are standing too proud from the process. This will improve polish purchase on the lap, increase friction, and provide troughs for small bits of swarf or balled-up polish to fall into, preventing scratches as it also speeds up polishing. The difference in a brushed lap surface on my BA5T and one that’s become very polished from use is perhaps 2 swipes to polish versus 50 – around 25 times faster.
Good luck; have fun; and post any questions below. I’ll do my best to answer.