Breaking Down Abrasives

Thank you for posting this 1967 article which I enjoyed reading very much. The word baroques was used instead of stones or rocks twice. This was a new term to me. When I tried to find out what it meant exactly, the meaning wasn't clear. Some meanings found on the internet led me to think it might be more about shape/size than merely a substitute for rocks. It might refer to a rock prepared to be worn on a person so of a convenient size and attractive appearance.

There are so many variables involved in tumbling and designing any kind of test that it drives me crazy to think about them. All the ones mentioned in this article, plus many others. They used pretty small barrels, and also small rocks. One additional variable I have noticed is the shape of the rocks. If I put in sharp rocks with all kinds of edges and corners on them in coarse grit, I don't see the grit broken down as rapidly as if the rocks start out pre-rounded such as beach stones, or as later in the coarse grit stages for rocks that started real rough. For instance, in a 40lb barrel, a pre-rounded load seems to always take a week before the slurry is about right and grit "gone". But for rough rock batches, I tend to go longer, such as 8, 9, or 10 days to see the same slurry results. What I mean by slurry results is a fairly repeatable result of batter-like consistency that when you rub it between your fingers reveals no grit grains that can be felt at all.

This article reminded me of a mistake I have been making for years potentially. When I measured my grit out into cups based upon the tablespoon method, I based it upon the barrel capacity lbs, such as the common Lorton 12lb barrel. I didn't weigh the rocks going in and have no idea if they weighed more or less than 12lbs. Same with all my other barrel sizes. My results seems to be okay after years of doing this, but out of curiosity now I think will weigh a few loads to see how much they compare to my barrel capacities (6, 12, 20, and 40lbs). I did weigh a 40lb barrel once after closing it and getting ready to put back on the shafts and it weighed 68lbs! Of course, this included the steel barrel, the rubber lids and liner, rocks, water, and grit. Really makes me wonder how much might have been just from the rocks.

The first paragraph on the 3rd page about 246 hours and times caused me to think about something that we all probably know is so obvious but never mention. That is, we could target a completion time by varying the grit used. For example, I am not retired, and have 8 barrels rolling. It's best for me to have most of the barrels come due on weekends, rather than evenings after I get home from work. I'm thankful that the guidelines in the literature for grit portions end up lasting right on a week for me, so a barrel I recharge on Sat morning will come due a week later on Sat morning, most of the time.

If I had a traveling job let's say that had me being gone for two weeks at a time, I could just test smaller and smaller grit portions until eventually it resulted in the barrels requiring 2 weeks to "come due" meaning use up the grit and be ready to recharge. That's based upon having those barrels continue to tumble for the full two weeks instead of having someone else go out and turn them off while I'm on my trip. This implies that electricity cost could be another variable because the faster the results the less electricity used. Another variable that I tested a few years back was about rock damage vs RPMs. This is a very complicated thing to figure out and probably involves also the barrel size, the barrel dimensions, the shape (round, hexagonal, etc.) of the barrel, the material of the liner, whether the liner has projections in it like some Covingtons, grit size, temperatures, and perhaps a dozen others I can't even think of. I enjoy dealing with less damage resulting from lower RPMs, so fewer rocks have to be redone or sawn, or discarded. A undamaged rock coming out of coarse gets to go on to the next grit level so saves coarse grit in that way. On the other hand, it might have spent more time in coarse due to lower RPMs so may have used more coarse grit in that way. But a rock damaged in coarse grit because of RPMs has to be kept in that stage longer which I don't like.

I haven't yet watched Rob's video to be able to see if that changes any of my thoughts.

This is my 10th year doing rotary tumbling and in the beginning believed this to be a very simple and brainless hobby. Man, was I ever wrong and none of us do the same thing which is so darn interesting.  Personally I'm very thankful this forum exists and am so thankful for the people who maintain it.  If I have a few minutes in any situation and want to exercise my brain, such as this time from an airport between flights, just glance in here at new topics and something is always interesting to read like this one!  For those of you also old enough to know what the Compuserve forums were, this is just like them but a few decades later.