herchenx
Cave Dweller
Member since January 2012
Posts: 3,360
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Post by herchenx on May 29, 2012 18:49:23 GMT -5
On the buy and sell section I posted about how to polish larger flats. I opted to not get the vibe from Chuck, but have a bead on a local seller who has a flat lap from Covington. Here's my question: do you use the same steel disc for all grits including polishing? Do you flip the big steel disc over to polish, or just use the same disc for everything? Or do you buy a separate disc for polishing? There is a fine layer of rust on the disc now, can I just use it like that and let the 120 SIC take care of the rust? LAST: What would a fair asking price for this be. It is not new, but looks barely used and runs fine. Thanks for any help.
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Post by gr on May 29, 2012 19:26:52 GMT -5
run some trash rock/ slabs with 120/220 to get the rust gone. you can use the same pan for all your grits. seperate pans, or dedicated pans, are better but expensive. just clean your pan REAL good between grits. for polishing you can cut a piece of indoor/outdoor carpet for, (to hold) your polishing medium. John, now I'm confused - What do you have exactly? a vibrating lap or a flat lap disc. I am assuming that it's a vibe lap by your questions. I'm not familiar with Covington products
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Post by jakesrocks on May 29, 2012 19:36:09 GMT -5
Covington still sells a 16" flat lap just like that. $1,750.00 for a 2 speed, and $1,325.00 for single speed. Does that one have the water supply can with it ? It should fit into that hole in the corner. Since the 20" is second hand, if you can get it for under $1,000.00, it should be a good deal.
If you get it, I'd swap you straight across for my 20" HP Vibrolap. Don
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Post by gr on May 29, 2012 19:41:19 GMT -5
Well, thanks Don! that clears up a few things. Don, would you concur my previous post or ? Just tryin to help John
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Post by jakesrocks on May 29, 2012 19:58:03 GMT -5
Actually, all the rust would come off with the first nodule he lapped. I haven't seen a rotating flat lap like that in a lot of years. The newer ones have a slight taper on one side of the disc, and flat on the other. For polishing, Covington used to have a 10" polish head that replaced the lap plate. All of the sanding was done on the lap, then change over to the polish head with either felt or leather on it. The rotating lap is faster, but more labor intensive. You can't walk away from it like you can a vibro lap. You have to hold your work piece in your hand, and work it across the plate. Most people like the vibrating laps because they can load them with rocks and walk away. I like the rotating laps, but I'm an old goat with lots of time to waste. lol
Oh, by the way, I have the 10" sanding and polishing heads that would fit it.
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Post by gr on May 29, 2012 20:00:52 GMT -5
Don
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Post by jakesrocks on May 29, 2012 20:19:21 GMT -5
Another thing that can be done with a rotating lap, that can't be done with a vibrolap. You can make an adapter to fit the arbor, and thread a pipe bell reducer on it . Instant old school, single head sphere machine. Just hold your rough sphere blank in a leather glove and rotate it in the pipe fitting. Once it starts getting smooth all around, it'll turn on its own. I've seen bowling ball size spheres made that way. But once again, very labor intensive work.
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Post by johnjsgems on May 29, 2012 20:47:14 GMT -5
I had a chance at one of my Texas shows to get a HP 18" rotating fl;at lap. The guy wanted $150 credit toward a purchase. I didn't have room to haul it home but would like to have one. Like Don I really think they are a lot better than vibe laps. Most people wouldn't want one so prices should be low. You can also buy magnetic diamond laps and magnetic Nova and polish laps from Diamond Pacific. Really expensive but killer performance.
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Post by jakesrocks on May 29, 2012 21:12:44 GMT -5
LOL. John, you wouldn't believe this HP vibrolap I have. It belonged to an old lady retired postal worker. She bought it new, and had no idea how to use it. She tried to do her rough lapping on the polish pad. She wore out the polish pad, right down to the metal backing. The lapping pan is still brand new. I bought a new polish pad from Diamond Pacific, but have never used the machine. Got it, a 24" HP saw, A 3" facetors saw, a gem drill, a big work bench , a bunch of findings, A small sphere machine and about 500 lbs of rocks for $1,000.00. That was back around 94.
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herchenx
Cave Dweller
Member since January 2012
Posts: 3,360
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Post by herchenx on May 30, 2012 18:10:50 GMT -5
Thanks all so much.
So Don: are you saying I need additional hardware to polish? I can't polish with this steel plate?
I know these are probably stupid and obvious questions, but I don't want to get into a "deal" that requires me to spend another $500 - $1000 just to get a shine.
The sphere idea is cool, never heard of that. I'm not afraid of the manual part, i find all this cathartic. I have heard that these are much faster than a vibrating lap though.
I don't think there is any sort of drip attachment with this one, but I can rig something up pretty easy.
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Post by jakesrocks on May 30, 2012 18:33:13 GMT -5
Covington still sells the 1/2 gallon water supply and an optional grit feed for these machines. They also carry the 10" aluminum sanding and polishing heads. The water supply will set you back $60.00 And the grit feed $63.00. The aluminum heads are $65.00. Those prices were from the 2011 catalog.
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Post by johnjsgems on May 30, 2012 19:25:12 GMT -5
All you would need to polish is a polish pad (felt, carpet, etc.) to lay on top of the really clean metal lap. At the club workshop where I used to live we had one and three people could use it at once (same grit, of course). We used a restaurant cooks salt shaker to sprinkle grit as needed and had a water drip plumbed into a water line. Pretty simple really.
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herchenx
Cave Dweller
Member since January 2012
Posts: 3,360
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Post by herchenx on May 30, 2012 19:33:20 GMT -5
So just laying it on the plate is adequate to polish, no adhesive. Nice. Thanks Don and all! I'll think about it.
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Post by jakesrocks on May 30, 2012 20:13:11 GMT -5
I hate to disagree with John, but with a spinning disc you'll need some way to secure the polish pad to the disc. Been a long time, but as I remember, a piece of wool carpet was used. It was larger diameter than the disc, and had grommets around the outer edge. They used the old fashioned screen door springs from grommet to grommet under the disc to hold the polish pad in place. Without fastening the pad, it would fly off the disc.
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LarryS
freely admits to licking rocks
SoCal desert rats
Member since August 2010
Posts: 781
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Post by LarryS on May 30, 2012 20:50:11 GMT -5
Bobby1 has a tutorial on the other board where he grinds/polishes large slabs using just a expando drum with a worn out 100 grit belt, dry. Don't forget to use a mask. Then a quick buff using polish. I've tried it and it works!
LarryS
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Post by jakesrocks on May 30, 2012 20:54:18 GMT -5
If you get that lap, check underneath and see if it has 2 or 3 stage step pulleys on the arbor and motor. If it does, do your grinding and sanding on the slowest speed. Using high speed will throw the grit and water off the lap plate. Use a higher speed for polishing.
Also, once you get past the first grinding stage make sure to keep a firm grip on your stone. In the finer grits the disc will try to grab the stone and throw it off the disc.
Spinning or vibrolap, grind a very slight bevel around the outer edge of your stone. This allows grit and water to get between the stone and lap plate. Without the bevel the sharp edge of the stone will push the grit ahead of it, and it will take a lot longer to grind it smooth.
The newer spinning laps have several ring grooves machined into their faces to help hold the grit. The older laps were just a flat plate, and do use more grit.
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