chilerock
off to a rocking start
Member since June 2018
Posts: 19
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Post by chilerock on Apr 24, 2022 11:28:59 GMT -5
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 disks. But don`t want to go the expense of diamond disks in 24". 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. Anyway, 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!!
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chilerock
off to a rocking start
Member since June 2018
Posts: 19
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Post by chilerock on Apr 24, 2022 17:59:33 GMT -5
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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herb
spending too much on rocks
Member since November 2011
Posts: 444
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Post by herb on Apr 25, 2022 10:14:18 GMT -5
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 disks. But don`t want to go the expense of diamond disks in 24". 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. Anyway, 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!! Do you have a 24 inch pan, or is it literally a flat plate? I have a 15 in flat lap pan. I use a plastic picnic spoon to measure out the grit. For a 15 inch lap, I use 4 semi heaping spoon fills. For a 24 in lap, you'd need around 10 spoonfuls. The grits I use are 200, 600, 1000, then polish. For the 200, 600, and 1000 stages I run for 4 hour cycles. At the end of the cycle, I clean off the the geodes by swishing them in a bucket of water and then rinse the pan out by pouring cups of water from the bucket in the pan to wash out the used grit into the bucket. I then repeat the process. Generally need 3 cycles of 4 hours for each grit. When i am ready to move onto the next grit, I take the pan and bucket outside and scrub and wash everything clean to make sure there is none of the previous grit left to contaminatethe next stage. For the polish. You need a pad of felt or low pile commercial carpet in the pan to hold the polishing grit. The polish doesnt wear out like the other grits so once the pad is charged with polish, you only occasionally need to add a little more. I've only ever used silicon carbide grit and aluminium oxide polish so can't say what else would work. If what you have is literally just a plate, then those are meant to have a constant slow drip of of water and grit slurry dripping in the center. The centrifugal force will spread the grit/water over the whole plate. With these, you just grind until the stage is done since there is new grit constantly added. Not sure how long a stage would take, never having used one. I would guess a few hours. Unless this is a home built lap or you know the motor was replaced on a commercial lap, I would not adjust the speed of the motor. Slowing it down will prevent the grit slurry from leaving the plate properly
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chilerock
off to a rocking start
Member since June 2018
Posts: 19
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Post by chilerock on Apr 25, 2022 20:01:04 GMT -5
Firstly, thanks for the advise from everyone. This is a plain flat lap with a 1/2 thick steel plate but it is not vibratory. It was built here in Chile South America. Original motor was 1400 RPM and many suggsted lower speeds. So, changed out the single phase original motor to a three phase 1350 RPM motor. But am also using a VFD, which allows complete speed control of the motor. We use a 8" Ameritech lap with diamond disks but do most of our work on a 6 wheeled Genie with diamond wheels. But 24" diamond plates are too pricy, even more so when imported, so looking to use this machine with loose grit. Larger stones are simply too big for the other mentioned machines that we use.
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chilerock
off to a rocking start
Member since June 2018
Posts: 19
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Post by chilerock on Apr 25, 2022 20:02:33 GMT -5
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jayhawk
off to a rocking start
Member since October 2021
Posts: 5
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Post by jayhawk on May 22, 2022 21:08:54 GMT -5
I was wondering if you had found an answer to your large flat lap? I also bought a very vintage large lap, nothing I can find fits the arbor hole, and I cant use no hole disks. I have resorted to glue, placed on an old record, and glue to put silicon carbide sandpaper on top of the record. Its a VERY slow process to grind down rocks, just wondering if you found a solution
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quartz
Cave Dweller
breakin' rocks in the hot sun
Member since February 2010
Posts: 3,340
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Post by quartz on May 22, 2022 22:42:38 GMT -5
I made a 20" rotary lap, use 80, 220, 600, and tripoli or cerium oxide polish. No set amount of grit, I sprinkle grit on when it feels like the grit is used up, very low tech. It runs at 120 RPM, about as fast as possible and yet not throw the grit off, VFD would be big advantage I think. Water via squirt bottle. No timeline, I run a rock until it gets smooth enough to move to next stage, and I am careful about how smooth my saw cuts are, saves grinding time.
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Post by manofglass on May 23, 2022 17:09:31 GMT -5
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