Covington vibrating lap

Start by grinding a very slight bevel all around the edge of each piece. This allows grit to get between the lap and the slab.

Start with 220 grit. Anything more course only wears the lap plate out quicker.

If you're lapping several pieces at the same time, stretch a rubber band around the outside of each piece. This acts as a bumper strip to cushion the pieces when they bang into each other.

If you're polishing slabs, they're too light. You'll have to add weight to them. I ordered 1/4 and 1/2 pound lead ingots to attach to the tops of slabs.

Make sure the slurry in your lap pan never dries out. Check often, and add a squirt of water as needed. But your pieces don't want to be swimming in water. Just wet enough to maintain a slurry.

Just search for small lead ingots on ebay. Or if there's an auto tire place near you, see if they'll let you have some old tire weights they've pulled off.

Fill the pan about 2/3 to 3/4 full. Leave some space for the slabs to move around.

For slabs, it's best to wrap the edges with a couple go-rounds of folded duct tape. I only use rubber bands for nodules that don't have a sharp slope. The bands won't stay on slabs very well unless the slab is really thick. What happens with the rubber bands a lot is that the band will come off the edge and go under the slab which causes an uneven grind or polish.

I use 1lb lead ingot weights on medium sized slabs and 2-3lbs on larger or very saw marked/scored slabs. Or I will arrange multiple 1lb ingots on a large slab. I'm doing a 9 1/2-10" by 4 1/2" Death Valley/Wingate Pass slab that has two one pounders in line. And also a Deschutes slab about 8in square-ish that has two ingots on it that are a tad heavier than 1lb. The rocks have to be tight to the grit. The old Lortone laps are notorious for hopping the rocks up/down and weight helps with those.

Another good thing to do is to cover the whole slab/ingot with duct tape slanted down to the edge of the slab. Or, if the slab isn't long and narrow or is too big, fold over some duct tape, leaving maybe 1/4" of stickum and make a sort of wall around the whole deal. It's inevitable that your water will be deep enough to splash onto the tops of flat slabs. When it does, it deposits grit there. Over the lenght of the grind, you can end up with fully a third or more of your grit riding atop the slabs rather than being in the pan working for a living like you paid for it too. Keeping the grit from getting stuck on the slabs saves a lot of grit/polish/$$. It's a little tedious at first but, after a while, you get really fast at "dressing" your rocks for their dance in the ol' jiggle pan. Make sure to strip off all of the tape, clean the rocks well, and apply new wraps before you proceed to the polish phase. It just takes a little grit wedged under a fold of tape to contaminate your polish. I don't usually redo the tape between grit phases. Overkill, imo. I usually do 60/90 - 220 - 600 grit grinds and occasionally 1000 or 1500 grit for obsidian and Montana Agate, followed by polishing with tin oxide. I run 60/90 for 14-20 hours. The longer you "pay your dues" at the coarser grits, the better you polish will be. I run 220 for the same time because the jump to 600 grit is bigger, though I've thought of doing a short-ish 400 grit grind in between. More time, more $$ and I really have no complaints doing it like I have for 3-4 years, now. The longer you run each phase, the better shine you'll get because the grit breaks down over time. A good 600 grit grind can end up with the grit being finer than 2400 in 14-20 hours.

You can get a perfectly flat surface and a glass shine on most harder rocks like Morissonite, Bruneau, Imperial jaspers and agates and thunder eggs. It does tend to make softer areas undercut but maybe no more than any other method. The matrix on Deming Agates is just awful for undercutting. It *is* somewhat slow but, with my 20" pan, I can do anywhere from 17 to over 30 slabs/nodules all at once, so it evens out that way as compared to using wheels, etc. And the colors pop brighter than using the heat-based methods, plus no micro-fine scratches. I've noticed that damp polishing generates a good bit of heat and sorta fogs the colors on rocks. I've had to take ones done that way and run them in my polish pan for maybe 6 hours to get the colors popping again.

Well, this was long, eh? I had a tips thread back before they changed the software with a lot of info on using a jiggle pan (vibrating lap) but it's gone, now, I guess. I might start another one as I've learned a lot in the 4 years I've been using this tool.
C-ya,
Rick

Make sure the unit is level (put a level across top of pan in several directions). I used scraps of hose as bumpers around rocks similar to the bumper ring around the pan edge.

i use a undercoat spray on my weights then just put a small drop of super glue inbetween the wieght and slab when you done just heat it up a bit and it will come right off