rockbrain
Cave Dweller 
Member since January 2022
Posts: 3,217
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Post by rockbrain on May 20, 2024 13:09:56 GMT -5
I'm ordering a magnetic master lap spin on for the end of my cab machine. It has a hard disc on it now but it's pretty fine. I mostly want to be able to more quickly clean up and polish the backs of cabs and some other small flats and small geodes. Since the Nova disc are over $75 each I'm going to try and use mostly hard disc from Hans Lapidary. They are $6.50. My question is about grit progression with all hard discs. They have 18 different grits between 46 and 3000. I've not really worked with a flat lap much and would appreciate any help.
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wpotterw
spending too much on rocks
Member since September 2016
Posts: 450 
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Post by wpotterw on May 20, 2024 15:42:49 GMT -5
I'm ordering a magnetic master lap spin on for the end of my cab machine. It has a hard disc on it now but it's pretty fine. I mostly want to be able to more quickly clean up and polish the backs of cabs and some other small flats and small geodes. Since the Nova disc are over $75 each I'm going to try and use mostly hard disc from Hans Lapidary. They are $6.50. My question is about grit progression with all hard discs. They have 18 different grits between 46 and 3000. I've not really worked with a flat lap much and would appreciate any help. If you have clean saw cuts, I'd say something in the 325 grit range to avoid scoring that can happen with 220 or lower. |
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rockbrain
Cave Dweller
Member since January 2022
Posts: 3,217
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Post by rockbrain on May 20, 2024 16:49:18 GMT -5
Thanks wpotterw, I'm getting magnetic disc so I can swap them out quickly and easily and go through a progression. I think the disc I have on the left side of the KN cabber is a 360 so I've already got it covered for fairly clean cab backs. I'm looking at starting with an 80 to remove saw marks, unevenness, etc. After that going to a 180 or 240 (they don't offer a 220). My real question is what to use after that. With a soft wheel it would be 280, 600, 1200, 3000. I didn't know how close I should stay to that progression with hard discs. |
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lapidary1234
spending too much on rocks
"If you like rocks you can't be all bad!!" ~ old timer quote
Member since October 2021
Posts: 338
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Post by lapidary1234 on May 27, 2024 16:38:32 GMT -5
I recently got a magnetic master lap for the end of my genie as well. It doesn't spin on tho, takes a 1/4"×20 screw.
I went with the magnetic novas from dp. I think they run $64 ea, so more than Chinese metal laps but less than the spin on nova plates. The magnetic nova discs also don't have the foam backing so I figured they'd work better for polishing slabs.
I bought the typical sequence of grits (60-3000). What I've noticed is most slabs i have don't need to be started at 60. 140 seems to be the sweet spot. 280 works as well on really slat slabs without any saw marks!
The issue I've had (used these less than 5 hours so far) is im getting subsurface scratches that seem out of place. Now I've heard that until novas are broken in they can and will leave scratches. I just have a hard time wrapping my head around how that can happen. Hopefully over time this situation will remedy itself.
All in all I am super happy with this approach as often times id rather just polish a slab instead of making a cabachon.
I also saw that thk.com (treasures Hong kong) sells magnetic metal hard laps for less than $20 each. I am thinking of buying a real coarse grit one of them to really chew through uneven rough I just haven't pulled the trigger yet!
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Maybe you can post some pictures here