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Author Topic: NEED ADVISE FOR 24" LAPPING PLATE  (Read 1453 times)

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CHILELAP

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NEED ADVISE FOR 24" LAPPING PLATE
« on: April 23, 2022, 09:48:15 PM »

Hello:  Bought a used 24" lap on the cheap and reconditioned it and changed motor to 3 phase with VFD to control speed. Now, have used 8 inch lap with diamond pads.  But don`t want to go the expense of diamond pads in 24".  Have heard that can use silicon carbide or other grits in a loose form on the plate.  Would be grateful to hear about what grits are normally used for this style (loose grit) and also if aluminum oxide grit can be used in this case, as well as silicon carbide or opther powders.  And about how is the grit applied to the plate and how does it stick? Ideas of working RPM`s would help also. Thanks in advance!!  PS: We will use this lap for polishing larger geode halves, as well as polishing some large quartz crystals, making flat sided figures, etc., all in semi precious stones.       
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Stonemon

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Re: NEED ADVISE FOR 24" LAPPING PLATE
« Reply #1 on: April 24, 2022, 09:26:47 AM »

Welcome!
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Bill

vitzitziltecpatl

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Re: NEED ADVISE FOR 24" LAPPING PLATE
« Reply #2 on: April 24, 2022, 09:55:01 AM »

Welcome to the Lapidary Forum.

Saw your question on another forum, and still don't have an answer. I know faceters use various types of laps that have to be charged in the manner you're talking about. Copper, tin, phenolic, etc, with a separate lap for each grit.

I'm sure someone will come up with some info.

R.U. Sirius

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Re: NEED ADVISE FOR 24" LAPPING PLATE
« Reply #3 on: April 24, 2022, 01:35:46 PM »

I've seen large laps with cast iron plates, SiC slurry is squirted on or brushed on as needed. Cannot find the exact video of a lapidary from Brazil I saw some time ago, but here is an example of a similar but smaller lap:

https://youtube.com/watch?v=FGyRBq63dfE
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55fossil

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Re: NEED ADVISE FOR 24" LAPPING PLATE
« Reply #4 on: April 25, 2022, 07:20:24 AM »

   Picture please so we know what we are talking about.   I had a 24 inch flat lap that had a smooth steel plate bottom and 4 inch steel sides.
    Just a matter of adding several tablespoons of grit and just enough water to make a slurry. Too little water and it just made dust, too much water and it did not polish well. I loved the results. Used 90 grit SIC on first polish, sometimes required more than one run of 90 grit to get smooth bottom on flats.
     Weights!  Except on very heavy stones it required a metal weight to be on top of the flats to get them to polish. Yes, this was tricky as the weights always wanted to vibrate off the stone so I used double sided tape to hold them in place.
    Every stone is different in how long to polish, etc...  Long but easy and forgiving learning curve.
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CHILELAP

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Re: NEED ADVISE FOR 24" LAPPING PLATE
« Reply #5 on: April 27, 2022, 05:24:05 AM »

Thanks to everyone for advise.  One other question concerning the same issue of lapping with loose grit, does anyone have any experience with using "grit miser" or "grit saver" or any other substance to help hold the grit on the lapping plate?
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55fossil

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Re: NEED ADVISE FOR 24" LAPPING PLATE
« Reply #6 on: April 27, 2022, 06:35:16 PM »

   Not the answer to your question, but...  All the vibrating laps I have ever used had a rim around the lap to keep the grit and water in place. As the lap runs it polishes the stone. The grit wears down as this occurs and polishes the rock better as the grit wears. With coarse grits this can take hours. There needs to be a supply of water so there is always a slurry. You do not want to add more grit after the lap has been running awhile because of the grit wearing down.
    I think I would add some time of rim around your lap to contain the slurry rather than try and make the grit stick to the plate. As I said, I have never used the type of lap you are showing so the picture does help.
   ????  By the way, how do you make the rock stay on the vibrating plate? Seems to me the rock would just wander off the plate.  It would be easy enough to make a two inch tall rim and glue it to the plate. Glad to hear if others have used a lap like yours and learn something new.
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CHILELAP

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Re: NEED ADVISE FOR 24" LAPPING PLATE
« Reply #7 on: April 28, 2022, 08:50:39 PM »

Thanks agai to all for the advise.  Just yesterday I finally got a friend who has been cutting and polishing stone in Chile for over 50 years, to come by and show us his technique for this machine, using loose grit. It`s actually a pretty simple technique, first spraying the spinning plate with water and then and spreading out loose grit made into a slurry ontop the plate. Then once starting to grind, reapplying as needed the same grit slurry with the same kitchen type scrubber directly on the plate just behind the stone that is being ground. As mentioned, we already do a fair amount of grinding and polishing on a 6 inch Genie and we also have an Ameritech 8 inch flat lap, in both cases with diamond wheels or plates. But this larger lap is simply for larger pieces that don`t fit on the smaller machines. A big advantage to hearing from several of you on this forum and others is your sharing about using of grits up to 1000 and even polish on these larger plate. My local friend was not well aware of this point, having only used 320 grit or lower on these larger machines and then going to some kind of large wheel for higher grains.   Anyway, now it`s our turn. Surely we`ll be in a learning curve for a while but with all of your advise and the mentioned local demo here, we feel ready to go.
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vitzitziltecpatl

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Re: NEED ADVISE FOR 24" LAPPING PLATE
« Reply #8 on: April 29, 2022, 07:02:09 AM »

You might be able to use a piece of indoor/outdoor carpet with a very low nap - especially for the higher grits - to hold the grit better and give you longer times between adding more grit.

This would, however, mean using a "feathering adhesive" of some type to hold the carpet down. Might work for you if you can come up with some carpet (or other material) you like for all the grits - even the coarse grit - that would eliminate the need to clean adhesive off of your lap plate to use it without a carpet pad.

People have used that type of carpet on low-speed vertical polishers with good results.

CHILELAP

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Re: NEED ADVISE FOR 24" LAPPING PLATE
« Reply #9 on: April 29, 2022, 07:18:45 AM »

Thanks!!
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vitzitziltecpatl

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Re: NEED ADVISE FOR 24" LAPPING PLATE
« Reply #10 on: April 29, 2022, 07:36:53 PM »

You're welcome. Don't know why I didn't think of that sooner... .
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