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Post by HankRocks on Jan 23, 2019 7:31:18 GMT -5
(not sure this belongs in this section) Anyone here have much experience with polishing with a Vibrating Lap. I have a old Lortone 20 inch model. It's been polishing real well on smaller halves and slabs, not more than 4 inches. Have noticed that with larger specimens there is a portion of the surface in the center that does not polish as well as the rest of the surface. It gets a somewhat of a matte finish. Puzzled as to what is causing this.
It's not related to weight as I have a large section of petrified wood, about 7 inches diameter by 6 inches tall, in the polish stage that has a very nice polish everywhere except in a 1 to 1 1/2 inch area in the center. The area is not a soft spot as the wood has consistent hardness all across the flat surface.
The pans I am using have a flat surface without the grid of grooves I see on some models, or the dimples I see on the Reciprolap. I understand that helps speed up grinding as grit gets under the rock better. Could that be my issue.
Tempted to take one of the specimens and see if I could finish polishing the center area on a diamond belt on an 8 in expando drum. Might just mess the rock up, nothing ventured, nothing gained.
Thanks Henry
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Post by johnjsgems on Jan 23, 2019 11:41:45 GMT -5
See if the pan is flat by putting a straight edge across it. I wore the center of one of my pans down to a slightly dished shape. It was scrap aluminum then. Also, is the rock surface completely flat? The belt should not hurt the rock as long as it is fine grit. If it is a matte finish you may have to back up to 1200 and work the whole surface for a uniform finish.
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Post by HankRocks on Jan 23, 2019 12:35:18 GMT -5
johnjsgems Thanks for the tip, need to go find an accurate straight edge and test the pan. Henry
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Post by HankRocks on Jan 23, 2019 14:01:20 GMT -5
johnjsgems I suppose that short of a machine shop to mill it flat and remove the dimple, a new pan would be in order. The cost of milling it might be more than a new one. Wonder if it would be possible to put a new bottom in with a new Aluminum plate, maybe 1/4" or 3/16" cut round and then "brazed" or "glued in". The cost will probably still be about the same as a new one. It just occurred to me, I have have 5 - 20 inch pans with my original 2 pan machine and 3 given to me. Two of these pans are Polishing pad lined with carpet. In theory they have always been used for polishing with the pads in them. Should be able to just swap and make one of the polishing pans a grinding pan and one of the dimpled pans a polishing pan. It will be carpet lined so the dimple underneath should not be an issue. Might work. Henry
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Post by johnjsgems on Jan 23, 2019 18:57:07 GMT -5
Definite maybe. Some pans are thick enough to be machined flat. With that many pans it doesn't sound cost effective. I don't know if the newer laps use same pans. Mine was the older model with tree balls between pan and base. I never had a great deal of luck with mine. If I had 4 rocks on, one would polish, two would need more, one was usually non cooperative. I agree a pan with dimples or grid work would likely work much better. Lap has to be dead level too.
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mikeinsjc
spending too much on rocks
Member since June 2010
Posts: 329
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Post by mikeinsjc on Feb 5, 2019 18:34:51 GMT -5
Hankrocks, it just occurred to me that if you are polishing, you should be on a carpet or felt, and not the bare pan.
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Post by HankRocks on Feb 5, 2019 19:13:36 GMT -5
Hankrocks, it just occurred to me that if you are polishing, you should be on a carpet or felt, and not the bare pan. Yes, I am using pads of indoor/outdoor carpet, very short weave. The polishing stage works real well. I have a run of larger halves using the "flat" pan that are in 600 right now. I go to polish tomorrowand we should know in a day or two how the test run went.
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