Some experiments with 3# tumblers
Oct 15, 2023 18:52:15 GMT -5
tkvancil, Starguy, and 12 more like this
Post by adam5 on Oct 15, 2023 18:52:15 GMT -5
I have been scouring the forum for information on how to tumble rocks. One thing that is clear to me is that, while there are a few clear cut dos and don'ts, there are multiple paths to shiny rocks 
One topic on which there isn't a consensus is slurry, particularly during the coarse stage. In some circles it is thought that a good slurry (not too thick or too thin) is needed to lift the grit and get optimal grinding. To achieve this, old slurry or clay is added. Also, instead of cleaning out once the grit is used up and starting fresh, many adjust the viscosity of the slurry and add grit to it.
I have done some experimenting with slurry in 3# barrels to see what works best. All the experiments were conducted with a CE dual tumbler that rotates at approximately 46 rpm and 60/90 SC grit. In the first experiment, I used drainage rock (gravel) bought from Lowe's. My goal was to use rocks that were uniform in composition. While I think that the results of Experiment #1 are valid, I was uphappy with how the drainage rock works and subsequently used a mix of quartz and jasper in Experiments #2 & #3.
Experiment #1:
Though few use borax in the coarse stage, since it is thought that borax helps to accelerate the development of slurry I compared tumbling rough rocks in grit and water versus grit and water/borax.
Barrel #1 had 746 grams of drainage rock (of various size), 52 grams of 60/90 SC grit, and 8 fluid ounces of water.
Barrel #2 had 746 grams of drainage rock, 52 grams of 60/90 SC grit, and 8 fluid ounces of water/borax.
After 7 days, the rocks in Barrel #1 weighed 502 grams for a change in weight of 32.7%.
After 7 days, the rocks in Barrel #2 weighed 583 grams for a change in weight of 23.2%.
The slurry in Barrel #2 was noticeably thicker than Barrel #1, but not so thick that rocks were stuck to the side of the barrel.
Experiment #2:
Barrel #1 contained 903 grams of pretumbled quartz (rounded but not ready for fine grinding) and small jasper from a container of aquarium rocks, 64 grams of 60/90 SC grit, and 8 fluid ounces of water.
Barrel #2 contained 902 grams of pretumbled quartz (rounded but not ready for fine grinding) and small jasper from a container of aquarium rocks, 64 grams of 60/90 SC grit, and 8 fluid ounces of a thick slurry (1.70 specific gravity) that I treated with Darvan 7 (a deflocculant used in pottery) to reduce the viscosity.
After 4 days, the grit was used up.
The rocks in Barrel #1 weighed 831 grams for a change in weight of 7.97%.
The rocks in Barrel #2 weighed 853 grams for a change in weight of 5.43%.
The slurry in Barrel #1 was watery. The slurry in Barrel #2 was very thick but still liquid. Like hush puppy batter.
Experiment #3
Barrel #1 contained 915 grams of pretumbled quartz (rounded but not ready for fine grinding) and small jasper from a container of aquarium rocks, 64 grams of 60/90 SC grit, and 8 fluid ounces of water.
Barrel #2 contained 914 grams of pretumbled quartz (rounded but not ready for fine grinding) and small jasper from a container of aquarium rocks, 64 grams of 60/90 SC grit, and 8 fluid ounces of a thin slurry (specific gravity less than 1.2).
After 3 days, the grit was used up in Barrel #2 and was either very fine or used up in Barrel #1.
The rocks in Barrel #1 weighed 854 grams for a change in weight of 6.57%.
The rocks in Barrel #2 weighed 866 grams for a change in weight of 5.43%.
The slurry in Barrel #1 was watery. The slurry in Barrel #2 was somewhat watery but thicker than the slurry in Barrel #1.
Conclusions:
1. 60/90 SC grit mixes well enough in a 3# barrel and does not require an additive.
2. When using 3# barrels and 60/90 SC grit, it is better to clean out and put in clean water and grit rather than leaving in the slurry.
3. When the rocks are rough, it takes a longer time to use up the grit. There are less points of contact between the rocks and, thus, less area at any given moment where grit is making effective contact with rock. This also explains why you should have a mix of smaller and larger rocks. Once the rocks have been rounded to some degree, the rocks make more contact and the grit works more efficiently and is used up quicker.
One topic on which there isn't a consensus is slurry, particularly during the coarse stage. In some circles it is thought that a good slurry (not too thick or too thin) is needed to lift the grit and get optimal grinding. To achieve this, old slurry or clay is added. Also, instead of cleaning out once the grit is used up and starting fresh, many adjust the viscosity of the slurry and add grit to it.
I have done some experimenting with slurry in 3# barrels to see what works best. All the experiments were conducted with a CE dual tumbler that rotates at approximately 46 rpm and 60/90 SC grit. In the first experiment, I used drainage rock (gravel) bought from Lowe's. My goal was to use rocks that were uniform in composition. While I think that the results of Experiment #1 are valid, I was uphappy with how the drainage rock works and subsequently used a mix of quartz and jasper in Experiments #2 & #3.
Experiment #1:
Though few use borax in the coarse stage, since it is thought that borax helps to accelerate the development of slurry I compared tumbling rough rocks in grit and water versus grit and water/borax.
Barrel #1 had 746 grams of drainage rock (of various size), 52 grams of 60/90 SC grit, and 8 fluid ounces of water.
Barrel #2 had 746 grams of drainage rock, 52 grams of 60/90 SC grit, and 8 fluid ounces of water/borax.
After 7 days, the rocks in Barrel #1 weighed 502 grams for a change in weight of 32.7%.
After 7 days, the rocks in Barrel #2 weighed 583 grams for a change in weight of 23.2%.
The slurry in Barrel #2 was noticeably thicker than Barrel #1, but not so thick that rocks were stuck to the side of the barrel.
Experiment #2:
Barrel #1 contained 903 grams of pretumbled quartz (rounded but not ready for fine grinding) and small jasper from a container of aquarium rocks, 64 grams of 60/90 SC grit, and 8 fluid ounces of water.
Barrel #2 contained 902 grams of pretumbled quartz (rounded but not ready for fine grinding) and small jasper from a container of aquarium rocks, 64 grams of 60/90 SC grit, and 8 fluid ounces of a thick slurry (1.70 specific gravity) that I treated with Darvan 7 (a deflocculant used in pottery) to reduce the viscosity.
After 4 days, the grit was used up.
The rocks in Barrel #1 weighed 831 grams for a change in weight of 7.97%.
The rocks in Barrel #2 weighed 853 grams for a change in weight of 5.43%.
The slurry in Barrel #1 was watery. The slurry in Barrel #2 was very thick but still liquid. Like hush puppy batter.
Experiment #3
Barrel #1 contained 915 grams of pretumbled quartz (rounded but not ready for fine grinding) and small jasper from a container of aquarium rocks, 64 grams of 60/90 SC grit, and 8 fluid ounces of water.
Barrel #2 contained 914 grams of pretumbled quartz (rounded but not ready for fine grinding) and small jasper from a container of aquarium rocks, 64 grams of 60/90 SC grit, and 8 fluid ounces of a thin slurry (specific gravity less than 1.2).
After 3 days, the grit was used up in Barrel #2 and was either very fine or used up in Barrel #1.
The rocks in Barrel #1 weighed 854 grams for a change in weight of 6.57%.
The rocks in Barrel #2 weighed 866 grams for a change in weight of 5.43%.
The slurry in Barrel #1 was watery. The slurry in Barrel #2 was somewhat watery but thicker than the slurry in Barrel #1.
Conclusions:
1. 60/90 SC grit mixes well enough in a 3# barrel and does not require an additive.
2. When using 3# barrels and 60/90 SC grit, it is better to clean out and put in clean water and grit rather than leaving in the slurry.
3. When the rocks are rough, it takes a longer time to use up the grit. There are less points of contact between the rocks and, thus, less area at any given moment where grit is making effective contact with rock. This also explains why you should have a mix of smaller and larger rocks. Once the rocks have been rounded to some degree, the rocks make more contact and the grit works more efficiently and is used up quicker.
