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Post by idahocollector on Mar 26, 2019 16:22:53 GMT -5
I’m looking for some recommendations for grinding equipment. I am new to lapidary, my main focus is on polishing slabs of various sizes (mostly large), and grinding away material on a slab so I can polish it flat. I have already sourced handheld polishers for polishing the slabs, and a method for polishing on a flat surface. What I am looking for is a grinder that I can use for agate and jasper slabs to carefully remove material so that the slabs can be polished flat. There are many handheld grinders out there, and standalone units like the Rock Rascal which is a 6” combination grinder/polisher and trim saw (which I have not used, I just see it listed for sale as an option, but the housing around the grinder may make it hard to grind the surfaces of large slabs). Since I am working with large slabs I have to be careful handling the slab and grinding away material (such as the slab saw “nibs” that are often on otherwise flat slabs). On some slabs I could just trim away the extra material, but most of the slabs I work with are rare material and I don’t want to lose any real estate, and I am not making cabs, though I might want to grind the edges of a slab to lightly shape in a few cases. Anyone have any suggestions? Really appreciate any pointers, information on what is out there that would work well for my particular applications.
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Post by Peruano on Mar 26, 2019 16:57:28 GMT -5
Bigger is better. You will want an 8" wheel, not a 6" or 4 ". Nibs will be easy with just about any 8" and working the perimeter to take off hard edges will work as long as you don't have small concavities or notches. My attempts at using a flat lap for polishing slabs has been frustrating, but that's one option. A vibratory lap would be slow but another option. Then there always is a large vibratory tumbler to polish faces after you've done the flattening. Do I sound like I'm suggesting a complete array of lapidary tools?
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quartz
Cave Dweller 
breakin' rocks in the hot sun
Member since February 2010
Posts: 3,359
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Post by quartz on Mar 26, 2019 23:22:12 GMT -5
One thing that may be helpful in answering your question is a size description of the pieces you intend to grind and polish. How big is "large"? Size and distance descriptions mean different things to different people.
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Post by idahocollector on Mar 28, 2019 19:38:15 GMT -5
Tom - Thanks for the tip on 8". What specific equipment do you recommend? There is an 8" Covington variable speed grinder-polisher for around $930 shipped. I have not used this type of equipment. I'd like an economical option if I can find it, but I realize the bigger the wheel the better for most applications. I have ruled out flat laps for polishing the slabs I have. They are mostly rare material, some stress fractures which I seal. My understanding is that flat laps are great for thick slabs or faced nodules that can be weighted down, and this is not safe for the slabs I have so I have opted for a handheld polisher method. This requires a flat slab though, with the saw nibs removed, so I need to remove them prior to polishing, and also grind around the edges helps chipping during polishing. I was hoping I could get away with a handheld grinder of some type as opposed to a large Covington and wonder if there is some mid-range option I can consider.
Larry - The slabs I am polishing range from 13" down to 2.5", but most are 6-11" in length and 4-8" in width. Many are 1/4" thick, but some are closer to 4mm and some are 6-7mm. Mostly Mohs scale 6.5-7 material.
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RWA3006
Cave Dweller
Member since March 2009
Posts: 4,642 
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Post by RWA3006 on Mar 28, 2019 20:02:09 GMT -5
idahocollector Welcome to the forum. You might want to take a look at a bull wheel. They have a 12" disc that can be handy for flat surfaces. Another option would be to mount a large diameter flat plate directly on a motor. There also might be some ideas for you within the home made equipment section. woodman has some interesting insights on large flat laps also.
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Post by rmf on Mar 28, 2019 20:21:39 GMT -5
idahocollector M&K makes an angle grinder that you can hook a hose to and water comes out the center, there is a ground fault interupter and it uses 4" diamond pads from 30 grit to 8000 or 14000. (Note: The pads take a while to break in) This is identical to the hardware they are using to make granite countertops. depending on where you live you may have a local dealer. Also they can do flat or uneven surfaces due to the flexibility of of the diamond disks. You are then limited by how far your reach is. I have one I polish P. Wood with. It works well. For truly flat grinding the Rose Recipro lap (I think Covington now sells them) is the fastest and flattest flat lap I have seen. This uses SiC grit on a heavy machined steel pan. It is messy. I think they come in 24" and 30" sizes. You can put multiple slabs in that. Typically you weigh them down with lead bricks and I found that hot glue around the edges works better than rubber hose bumpers. I have also used large diameter PVC pipe with multiple 3-4" Brazilian Agates set in concrete inside the PVC pipe 12" diameter 3" long (It maks a 3" tall ring and holds the rock together so no bumping). The flat lap does not fix the nibs left by the saw just use a regular SiC or Diamond wheel to grind those off first before using a reciprolap or a vib lap.
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Post by woodman on Mar 29, 2019 9:49:06 GMT -5
To remove the nibs left by a slab saw all i usse is a 4 inch diamond blade on an angle grinder. works great for shaping also..
search thru all my posts and you will find photos of my flat lap and polisher. on the real large slabs I do use the hand held polishers and diamond pads to prep and polishing pad with cerium oxide to polish.
You can never have too much equipment.
have fun!
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Post by woodman on Mar 29, 2019 13:14:43 GMT -5
Tom - Thanks for the tip on 8". What specific equipment do you recommend? There is an 8" Covington variable speed grinder-polisher for around $930 shipped. I have not used this type of equipment. I'd like an economical option if I can find it, but I realize the bigger the wheel the better for most applications. I have ruled out flat laps for polishing the slabs I have. They are mostly rare material, some stress fractures which I seal. My understanding is that flat laps are great for thick slabs or faced nodules that can be weighted down, and this is not safe for the slabs I have so I have opted for a handheld polisher method. This requires a flat slab though, with the saw nibs removed, so I need to remove them prior to polishing, and also grind around the edges helps chipping during polishing. I was hoping I could get away with a handheld grinder of some type as opposed to a large Covington and wonder if there is some mid-range option I can consider. Larry - The slabs I am polishing range from 13" down to 2.5", but most are 6-11" in length and 4-8" in width. Many are 1/4" thick, but some are closer to 4mm and some are 6-7mm. Mostly Mohs scale 6.5-7 material. For the size of slabs you are talking about, a bull wheel would work it you are capable of holding the heaver slabs while sanding on them even a 13 inch slab can get heavy depending on how thick it is. I start slabs on my flat lap to remove saw marks, then move to a bull wheel with 100 grit belt, then to 220 grit belt, then go to a 400 grit belt. at this stage they look pretty good but do not have a good polish. I then take them to my rotary polish machine and run them until I am happy with the polish. Like I said before, I knock off the nibs with 4 inch diamond blade on angle grinder before I put them on the flat lap. hope this gives you some idea of how I process slabs! |
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vwfence
has rocks in the head
Member since January 2013
Posts: 567
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Post by vwfence on Apr 1, 2019 9:11:47 GMT -5
what material are the rare slabs you arre wanting to work ? depending on type of material would kind of dictate what i used to work them with . I have a homemade machine that takes 7 inch changeable diamond pads that can do a lot of different things , but it wont work on big septarianes
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Post by idahocollector on Apr 3, 2019 17:08:18 GMT -5
To remove the nibs left by a slab saw all i usse is a 4 inch diamond blade on an angle grinder. works great for shaping also.. search thru all my posts and you will find photos of my flat lap and polisher. on the real large slabs I do use the hand held polishers and diamond pads to prep and polishing pad with cerium oxide to polish. You can never have too much equipment. have fun! Thank you Woodman. This is the route I'd like to take. Would appreciate knowing which angle grinder models you've used reliably. I'd like to find an angle grinder that has a good variable speed range. I have read several of your posts in the past on hand-held polishers, it helped me develop my present system of sanding/polishing large slabs. |
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goatgrinder
spending too much on rocks
Make mine a man cave
Member since January 2017
Posts: 368
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Post by goatgrinder on Apr 3, 2019 18:23:45 GMT -5
I have a 20' vibe lap wheel (lortone) for polishing really big flat faces, think bookends, and a 16' rotary (spinning) forgot who made it, lap for doing the same thing but with more mess. Bought both very expensive when new items on the cheap 'cuz they were used. Both are in my basement shop but really should be outside. Size matters.
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goatgrinder
spending too much on rocks
Make mine a man cave
Member since January 2017
Posts: 368
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Post by goatgrinder on Apr 3, 2019 18:28:40 GMT -5
Oh yeah, go to youtube for vids about using vibe and rotary laps. Eezy peezy.
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Post by woodman on Apr 3, 2019 20:01:23 GMT -5
To remove the nibs left by a slab saw all i usse is a 4 inch diamond blade on an angle grinder. works great for shaping also.. search thru all my posts and you will find photos of my flat lap and polisher. on the real large slabs I do use the hand held polishers and diamond pads to prep and polishing pad with cerium oxide to polish. You can never have too much equipment. have fun! Thank you Woodman. This is the route I'd like to take. Would appreciate knowing which angle grinder models you've used reliably. I'd like to find an angle grinder that has a good variable speed range. I have read several of your posts in the past on hand-held polishers, it helped me develop my present system of sanding/polishing large slabs. All I use for 4 inch angle grinders are the cheap ones from harbour freight. don't need variable speed on them |
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