mikeinsjc
spending too much on rocks
Member since June 2010
Posts: 329
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Post by mikeinsjc on Oct 2, 2010 9:38:08 GMT -5
I'm new to the forum,and hope its ok to ask this question here. What are some ways to remove saw marks? Please be specific so I will know what to purchase. I already have an arbor with an 8x3 expando-drum. Should I just spring for a diamond belt for it? If so, what grit? It seems silicon carbide wears out way too quickly, but then I don't really know what I'm doing yet. Thanks.
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drjo
fully equipped rock polisher
Honduran Opal & DIY Nut
Member since May 2008
Posts: 1,581
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Post by drjo on Oct 2, 2010 10:35:35 GMT -5
Of course it depends on the hardness of the stone and how bad (deep) the saw marks are, but you'll need several grits ranging fro 80 to possibly 3000 (i.e. 120, 220, 325, 400, 600, 800, 1200 for a smooth cut to a nice finish), get all the scratches out by the 600 then you start polishing.
Diamond can wear out fast if you press to hard too. SiC belts take a light touch and patience.
And both need LOTS of water!
Dr Joe
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Post by deb193redux on Oct 2, 2010 12:00:28 GMT -5
If it is just visible marks, less than 1/16 inch in height. The sanding belts make sense. If you also want to polish, then higher grits will be needed too. At 35+ per belt you can quickly spend hundreds.
If the marks are more pronounced. Grinding as opposed to sanding is needed. This is best done with a hard diamond wheel. Around 100g.
You might be able to use Sic for some of the medium-high belts to save money. Maybe 1200, 3000 in SIc. Go back to diamond fro 14000 or 25000.
Any numbs or other large features should be struck off with a hammer or chisel - not sanded off.
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Post by bobby1 on Oct 2, 2010 21:23:36 GMT -5
Wear a dust mask, sand first with a dry 80 grit Silicon Carbide belt on an expando drum, then go to a well worn 100 or 200 dry. The resulting sanding marks should be very fine. I then take the rock or slab to my carpet covered polishing wheel with cerium Oxide. Used as they should be a Silicon Carbide belt lasts me for 3 to 5 years. They are the only sanding belts that I have ever needed or used. Bob
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mikeinsjc
spending too much on rocks
Member since June 2010
Posts: 329
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Post by mikeinsjc on Oct 3, 2010 8:39:48 GMT -5
Bob, sounds like you have a system that works for you. Why do some say silicon carbide should be run wet, others dry? Do you think running silicon carbide wet would prolong the belt life? I use wet/dry silicon carbide sheets for auto body work, but don't know if that is some special paper or if all silicon carbide can be used wet. Also , I assume if I use well-worn 100-200 grit belts, thats probably the equivalent of using 400-600 belts, so I really don't need to worry about purchasing the finer grit belts?
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Post by johnjsgems on Oct 3, 2010 9:10:40 GMT -5
I hope by dust mask he means respirator mask, not the $3 dust mask. SC belts are "wet or dry". Rock dust is hazardous so water is primarily for safety. I've seen rocks "polished" by dry sanding with 600 belts.
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drjo
fully equipped rock polisher
Honduran Opal & DIY Nut
Member since May 2008
Posts: 1,581
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Post by drjo on Oct 3, 2010 18:50:05 GMT -5
Water also helps remove the rock dust and keeps the paper from clogging up, removes heat from the stones surface and it does prolong belt life.
You don't wear a belt down evenly so your only going to cause yourself grief trying to get rid of scratches that your just putting back with the worn belt. SiC belts are only $1.50 to $2.00 each so it's not worth the aggravation.
Dr Joe
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Post by Hard Rock Cafe on Oct 5, 2010 12:32:13 GMT -5
There's no arguing with Bob's results, but it must have taken him a lot more patience than I have to master his technique. I was going through SiC belts in a hurry before I switched to diamond.
I use fewer steps than recommended above: 220, 600, 1200, 3000, polish. Your mileage may vary.
Chuck
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