Archive Message Index Start New Topic Photo Gallery FAQ and Use Tips Bob's Rock Shop

Posted in response to How much Grit to use ? from Wayne Rasmussen on September 09, 2004 at 03:22:26:

Re: How much Grit to use ?

Did a Google search and found a few sites with information. Here are the results from that search:

Tumbling Instructions for Lortone brand rotary tumblers:

1. Fill the tumbler barrel 2/3rds to3/4ths full with rocks.
2. Add water to just below the top of the rocks (so you can see it between the rocks, but don't cover the rock).
3. Add grit. Barrel Size 60/90(step 1) 120/220(step 2) Prepolish(step 3) Polish(step 4) grit in tablespoons
1.5# 4
3# 4
4.5# 8
6# 10
12# 20
4. Let each step run 7-10 days.
5. Make sure there is no grit transferred from one step to the next.

Place 1 and 1/2 heaped tablespoons of 80 Grit into the barrel per 1 and 1/2 LB of rock used. So for a 3LB barrel place 3 heaped tablespoons in. This is a rough guideline - the harder the rock the faster the process is with more grit (only around 1 tablespoon more though) the softer the rock, the less you can use - (again - only around 1 tablespoon less). With 1 and 1/2 of 80 Grit per 1 and 1/2 LB of rock you can't really go wrong.

COARSE GRIND
3. The amount of stones put in a tumbler barrel depends on the size of the barrel and the stones themselves. The best tumbling action occurs when the barrel is filled 50% to 60% of its capacity. Fill the
barrel with your stones to 1/2" above the half-way mark. Remove the stones and weight them. This weight will help you to determine how much grit is needed. Record this weight for future reference. Use the following ratio to determine the amount of silicon carbide grit needed for your batch:

One pound of grit per eight to ten pounds of rock


How much grit do I use?

I use about 1 ounce of grit per pound of rock for the grinding stages, and about a 1/2 ounce for the pre-polish and polish stages.


OK Now here is what I do. I put in what I think is appropriate (I know that doesn't help). It is just a guesstamate with me. I run for about a week then I check and see if the slurry is where I want it to be. If too thin I add more grit. If too thick I add more water. Simple as that. With the load you have I would probably start at about 20 lbs of coarse and check in a week or so. However with that kind of weight, rather than man handling it every time, you would want to guess pretty close the first time.

My tumbling differs from many people's. I will run 16-18 weeks on course only. As they tumble the rocks break the coarse down to finer and finer particles. Where eventually they are fine enough for a pre-polish. I check the rocks after about a week or two. The course does most of it's work during that time. If the rocks are not as rounded as I like I will add more course (about 1/4 to 1/2 of first load then continue the run.

At the end of 16-18 weeks I will pull a couple of stones and clean them thoroughly. I go to my polish pad on the cabbing machine and hit the rocks and see if a shine comes up. If so I go to polish. If not I go to pre-polish for a couple of weeks more then to polish. It is rare but I have gone to the pre-polish a few times, but most times I get a nice finish.

I use only course because it is the cheapest one. I use 60/90 again it is cheaper ungraded.

Another money saving idea is to reuse your polish. Since polish does not break down like grit will it can continue to work for long time periods. My current polish has two years of tumbling on it. The secret here is to make absolutely sure the polish does not get contaminated. In other words wash thoroughly all the rocks in the tumbler. After a complete washing I will run the tumbler and rocks with Dreft baby laundry detergent. (At 55 that is the only thing I hope I ever have to use that soap for. LOL) I load everything back in the tumbler and run it for a couple of hours in the Dreft. Caution here is that the Dreft makes everything very, very slick. If you are tumbling big rocks make sure you have a good grip when you pull it from the tumbler and don't let it slip out of your hands onto your foot. It will hurt. I use a large collander and a sealable plastic bowl to drain the polish from the barrel. In your case it will be a sizable bowl and collander. I seal the lid of the polish to eliminate contamination and let it set for a week or so. I then take a small hose and drain off the top water. The polish will have separated from the water and settle to the bottom. Here is a thought. Since you will be using a large amount of polish you might want to try a large new trash can as a reservoir. After the first time you can check the can after the polish settles out and install a small tap on the side of the trash can just above the polish level. Then you could drain the water just by opening the tap.

The polish will continue to settle for several weeks after the initial clearing. WE have very hot days around here so I vent the bowl and let the water evaporate. Eventually I get a dried cake of polish. When I am ready to polish again I just drop the cake in the tumbler. A small word of caution here. When a dried cake of polish is put into water it will suddenly absorb the new moisture and can cause minor expansion "explosions". Nothing harmful just shocking if you are not prepared for it. The first time I did it, part of the polish chunk popped out onto the floor. Contaminated, oops. (May not have been but I wouldn't take the chance.) I occasionally add new polish, because you will lose some since ir adheres to the rocks and the sides of the tumbler.

From Larry - September 09, 2004 at 09:19:59
Email: larry.mcauley[ ]twc.state.tx.us

Archive Message Index Start New Topic Photo Gallery FAQ and Use Tips Bob's Rock Shop

Meteorites   Polished Spheres  
Polished Eggs and Hearts   Polished Freeforms and Tumbled Stones   Mineral, Geology & Collecting Books  

Bob Keller