djalley
off to a rocking start
Member since January 2007
Posts: 18
|
Post by djalley on Jul 8, 2008 12:27:35 GMT -5
Holy smokes it takes a while to tumble granite.
A friend of mine had a few slabs of old granite and gave them to me. THey looked GREAT in coloring so I decided to give it a try. After a month on 60/90 grit (with changing grit weekly), there wasn't a lot of difference. So, I decided to use something grittier.
I had a small cup of super fine rock that was the results of all my previous tumbling, where rock chipped off and made a small shard as it went through the tumbling process. These were generally in the 3-5 mm range in size. I decided to add this cup to the grit and tumbled the granite this way.
It worked.
In one week the granite was rounded and smooth. Another week in prepolish and they looked great when wet. I didn't add the fine rocks to this stage.
They're in Polish now, and I'm letting it go a week. I'm anxious to see what they look like when dry.
Anyone else have experience tumbling granite?
D
|
|
|
|
Post by Toad on Jul 8, 2008 13:17:39 GMT -5
Yes, what a fiasco. It never worked for me. They shaped fine in a rotary with 60/90, but because of the makeup of the granite - various minerals with different hardness - I was rarely able to get a smooth finish. Inevitably, some of the softer components would get ground out and and leave pits. Only some very small pieces made it all the way through to polish. I'll never do it again. It's a shame as granite does have some nice varities - as you said. Glad to see you're having some luck with it.
|
|
djalley
off to a rocking start
Member since January 2007
Posts: 18
|
Post by djalley on Jul 14, 2008 11:39:28 GMT -5
Well, the granite came out of Polish over the weekend and I did see that there were several rocks with pits in them, like you said. However, there were about 10 of them that look like they remained quite smooth.
I put them all back in, because the polish on them wasn't very glossy. I'll give it another week or two and see how they do.
D
|
|
|
|
Post by LCARS on Jul 14, 2008 12:14:23 GMT -5
Why did you take the little bits out?  They're just as important in the polish stage, especially if you're not using any pellet fill for cushioning and you definately want that with granite. I have several bags with rock shards left over from previous batches that I can add as supplemental filler and cushioning. |
|
rollingstone
starting to spend too much on rocks
Member since July 2009
Posts: 236
|
Post by rollingstone on Jul 14, 2008 20:04:24 GMT -5
Granite can be okay, but you've got to take a couple precautions. First, try and choose a sample without much mica in it, because the mica will flake out or erode out, leaving surface pits. And when the polish stage is completed and you've rinsed out the barrel and rocks, keep the rocks wet and return them to the barrel with lots of cushioning pellets and soap, and give them a good run (hours at least, or longer) to get any residual polish out of any surface pits on the granite. If you let the rocks dry out after polish, the polish will harden like cement in the pits, and no amount of cleaning stage will remove it. -Don rough granite:  Finished stones from the chunk above:  |
|
|
|
Post by sitnwrap on Jul 14, 2008 21:49:51 GMT -5
Well I'll be! I always wondered what granite would look like polished as it is the most abundant material I come across when out and about.
Very informative thread. djalley, looking forward to seeing the results of your tumbled Granite.
|
|
headupdef
off to a rocking start
Member since June 2008
Posts: 7
|
Post by headupdef on Jul 15, 2008 12:21:03 GMT -5
Those are really nice! I have some in the polish stage rightnow and hopefully they'll be just as nice.
|
|
djalley
off to a rocking start
Member since January 2007
Posts: 18
|
Post by djalley on Jul 16, 2008 11:58:46 GMT -5
I am indeed using pellets to cushion the granite.
I took the small rocks out because I didn't like the idea of them banging into the larger ones. My thought process on this was that if a larger rock has a soft spot in it, another large rock hitting it would be less likely to "needle into" the soft spot just from a surface area standpoint. Kinda like it being easier to dent your neighbor's car's quarter panel with a ball-peen hammer than a trash can lid. =) The smaller rocks gave the potential for a much more local, and concentrated impact than the large rock. The cushioning pellets further reduced this risk. I thought this would minimize the pitting. Considering I have about 10 rocks with minimal or no pitting evident, I'm standing by my decision. But the next batch I'll try to leave them in and compare results. =)
D
|
|
|
|
Post by Toad on Jul 16, 2008 12:22:40 GMT -5
Well, the granite came out of Polish over the weekend and I did see that there were several rocks with pits in them, like you said. However, there were about 10 of them that look like they remained quite smooth. I put them all back in, because the polish on them wasn't very glossy. I'll give it another week or two and see how they do. D Mixing smooth stones with those you know are damaged (pits & etc) can lead to the smooth stones being damaged. For me, damaged stones never left 60/90 until they were smooth or wore away... |
|
