What Is the Optimal Amount of Grit to Use in a Rock Tumbler?

Get the most out of your tumbling grit. I was really surprised by the results of my experiment to determine the most efficient use of coarse grit in a tumbler.
Because of many comments on this video, I did a follow up experiment here: • Optimal Amount of Tumb...
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[@jonathanyoung7785]

I've got a theory. What causes grit to wear down the rocks is friction, which is to say pressure + movement. The tumbling action creates friction as rocks slide past and roll over top each other. (If you overfill the barrel and the rocks cannot move freely, the grit and water splashing around inside the barrel will not grind down the rocks.) When two rocks are on a collision course -- and there is grit stuck to the rocks -- the friction occurs between the rocks and the grit. The more pressure, the more friction, and the more grinding action. It's like pressing harder with a piece of sandpaper. The amount of grit probably impacts the amount of pressure, and thus the amount of frictional force. If there is too much grit, the tumbling energy will be absorbed by the grit, as the grit is squeezed out from between the rocks without really digging into the surfaces of the rocks. Similarly, the more pieces of grit that are stuck between two rocks, the less pressure there will be as between the surface of the rocks and a specific piece of grit. (It's an issue of pressure decreasing with surface area, like lying on one nail vs. a bed of nails.) I suspect that the ideal amount of grit is just enough so that there is a very thin layer of grit between the rocks. With a thin layer, the grit will not cushion the tumbling action, and the pressure / friction will not be dispersed excessively over too much surface area. Too much grit may also result in the grit being broken down primarily by being ground into other pieces of grit vs being scraped against the surface of a rock. You could think of this as the rocks grinding down the grit, as opposed to the grit grinding down the rocks. Grit breaking down grit is counterproductive, which could be why less can be more, as suggested by your experiment. For anyone who has made it this far, you might as well tell me what you think of my theory. I am not overly attached to it, so feel free to agree, disagree, or improve upon it. Thanks!

[@MichiganRocks]

That's a better theory than what I came up with and I think it makes a lot of sense. I like your bed of nails example, that really makes it clear to me. I'm also really interested in what others that might have more experience in this area might think. Thanks for taking the time to write that up!

[@nevetsrock]

Seams reasonable. There’s just too many variables to be sure what’s going on. Could a more watery slurry suspend the grit and cushion it thus preserving it. Or does it tumble faster breaking the grit even faster? Does the rate at which the slurry thickens affect speed at which the grit breaks down? Does a thicker slurry apply pressure to the grit or clog the sandpaper? Certain rocks can absorb more H2O. Is hard water better for grinding, worse for polishing .Temperature is always a factor. It would clinical trials to be definitive 😂. You guys broke it down pretty good though. Probably better than it should. Fun to think about. He does a good job at taking your mind off things for a while. Happy Holidays

[@MichiganRocks]

Yep, lots of variables. Hopefully, I did a decent job of eliminating most of them for this very specific experiment.

[@valsummers5330]

This was a great example of the scientific process Generated a bunch of questions and answers✅✅

[@Mike-br8vb]

I've learned something here, a long read😂 but worth it! Thanks guys!

[@darkwood777]

Interesting. I know you said you weren't going to do it, but redoing the experiment with 1 and 2 tablespoons of grit might surprise you further. I would also redo the 3 spoon test two more times and look at the mean and variance across 3 samples of the 3 tablespoon test. If the result is highly variable, you have to wonder what factor is causing that to happen.

[@MichiganRocks]

I thought about doing this for a second week, but weighing all those rocks just takes so long. I figured with four barrels coming out pretty much the same, I had pretty good evidence. I am curious about using a smaller amount though. I don't plan to redo this experiment anytime soon, but maybe some day. I have a couple other experiments planned.

[@jenniferbutcher8393]

Yes! I agree! I'd love to see this run with less grit...if successful, it could really save some money in the long run. I've been running my first 2 3lb tumblers for 4 weeks now, Saturday is my day to peek inside, rinse and add fresh water and grit. Last time i added 4 Tbs. in like you do, but this time I'll put just 3 based on this outcome! Thanks for doing such great research....and looking forward to more😊

[@miltonthecat2240]

@@MichiganRocks Hey Rob - judging by the numerous requests, your fans are on the edge of their seats on this optimal-number-of-tbsp mystery. I definitely hear ya on the time limitations for experimentation, though - you have to pick and choose and prioritize your time or this could easily turn into a Master's thesis project. But maybe you could reduce the weighing/sorting/matching step by using that "Large Ceramic Media", from Kingsley North or The Rock Shed, as the target "rocks". There are other larger size ceramic tumbling media available from industrial suppliers that might be a better stand-in for target rocks (e.g. a "1" x 1" V-Cylindrical" material from McMaster-Carr). This would reduce the effort to counting the pieces of ceramic media and weighing the the whole batch at once.

[@FSCHW]

This was very good. I follow a few channels. I think MeMiner uses 2 tbsp in his.

[@MichiganRocks]

@@miltonthecat2240 Ceramic is harder than most rocks I tumble, so that wouldn't really work. I'll consider doing another experiment.

[@patriciamckean4186]

Your attention to detail is very appreciated. Thanks for the instant gratification with the help of your video.

[@MichiganRocks]

You're welcome, Patricia.

[@cottageinthecity2]

Thank you for all you do to spread the love of rocks! My family (me, especially I guess) have officially fallen down the rockhounding rabbit hole. Your well-produced videos have inspired many trips to the UP and helped us gear up, better understand, and process our treasures. It is obviously a labor of love, but also a lot of work. Thank you!

[@nevetsrock]

Welcome to the rockhounding rabbit hole. Remember to always share the rocks

[@MichiganRocks]

You're welcome. It is a lot of work, but as you said, I enjoy it.

[@leisuretimeadventures]

Wasn't expecting this as the result either, but great experiment. Your videos are so useful to those of us just starting out.

[@gem6240]

Another great "barrel full" of information! Thanks Rob!

[@MichiganRocks]

You're welcome, Gem.

[@uberrainman]

Great video. I just started tumbling recently and have been using 3 tbsp in my 3 pound barrels after watching your earlier recommendations. I've had great results and this just re-enforces that decision!

[@MichiganRocks]

That's what I'll be using from now on.

[@coryO311]

I am new to Rock Tumbling and after watching many KZbin videos elsewhere you are definitely my go to source for learning information regarding rock tumbling. Experiments like this one show how you are not simply following directions someone else wrote on paper. I was reading an older forum where the person posting owned a lapidary shop and orders aluminum oxide grit by the ton for resale. The person made a wonderful point about how rock tumbling grit is technically sand blasting media simply relabeled as rock tumbling grit with a premium price added onto it for resale. They also stated that no brand is technically any better than another since aluminum oxide is exactly the same material. With over 90% of it coming from China, the difference occurs when a distributor in China adds filler material to cut back on their cost before shipping it to the US. The person stated this is only visible when examining it under a microscope and with good grit you will see high quality green crystals while in lower grade aluminum oxide you will also see the same high quality green crystals mixed with up to 50% “popcorn filler". The person did not elaborate on what they meant by “popcorn filler” but I took it as being a descriptive for the filler materials shape under a microscope and not as actual crushed popcorn. After hours of shopping around I can confirm that where you purchase step 1 grit seems to be the cheapest rock tumbling grit available that I can find. Their 45lbs of Silicon Carbide 60 comes to a total cost of $139.49 after shipping. Though I have also found 50lbs of sand blasting Silicon Carbide 70 for as low as $81.97 after shipping. I cannot personally speak on behalf of its quality but that is a savings of $57.52 with an additional 5lbs of free grit, or $3.09 a lbs for rock tumbling grit versus $1.63 a lbs for sand blasting grit. Now one is 60 grit while the other is 70 grit and since I am new to rock tumbling the numerous grit sizes are the most confusing part to me. I do understand what grit size means when correlating to sandpaper so these grit sizes should also affect rocks in a similar manor?

[@MichiganRocks]

The grit size for tumbling grit works just like sand paper. Bigger numbers mean smaller particle sizes. I hadn't heard that filler is used in some grits, although that shouldn't surprise me. People are always trying to cut corners. I have been happy with the Rock Shed and Kingsley North's grits, so I just keep buying those.

[@scottbutton6467]

Hi Cory. Just curious, where are you finding the 70 grit for $80 shipped. I am very interested in purchasing some bulk grit.

[@coryO311]

⁠@@scottbutton6467 Hello Scott, It actually ended up costing me less than $70 shipped. My grand total after taxes and shipping came to $60.40 for 50lbs of 70 grit in a nice resealable 4 gallon bucket. At the time it was $20 Off for Inside Track Club Members when I purchased it and membership is $29.99 a year or $44.99 for 2 years. Normal cost is $69.99 plus taxes, and surprisingly only $6.99 for shipping. After using this grit for the past month I can honestly say it has worked way better than any of the free grit that came with my 3 tumblers. My first being the National Geographic Platinum Series Ultra Quiet 2lbs tumbler that I bought for my kids. I have nothing good to say about that tumbler besides that a Christmas toy for my kids got me interested in the hobby. I only have great things to say about my other two tumblers, Extreme Tumblers Rebel 17, 17lb rock tumbler and the Raytech Tumble-Vibe 10, 8lb vibratory tumbler. The Tumble-Vibe 10 is a bit of a pain to clean out compared to something like a Lot-O-Tumbler but the reasonable cost and convenience of polishing 8lb at once is worth the hassle to me. The stage 1 grit that came with the Tumble-Vibe 10 was silicone carbide 100/120 and luckily “Michigan Rocks” taught me in another video to only do stages 3 and 4 in vibratory tumblers. The 100/120 grit seemed about worthless in my 2 rotary tumblers and took many weeks and fresh grit refills to do much of anything. The other two tumblers came with 60/80 grit which worked well but took 10-14 days to get similar results to what this cheap 70 grit is giving me in a 7 day period. I do not know much about rock types and have been tumbling large variety packs of colorful mixed hard stone and over 30lb of Onondaga chert. I discovered a glacial erratics of Onondaga chert that travelled over 200 miles during 1 of 7 large glacial movements that carved out the valleys and streams in NW Pennsylvania where I live. I am not positive of the Mohs hardness scale of this chert but in general chert seems to fall in the 6.5-7 range. Sorry about writing such a long reply but cheap $70 grit would be a waste of time and money if it did not work well. I wanted to give a thorough explanation of my limited experience and the tumblers I am using. This is the first stage 1 grit that I have ever used besides the free grit that came with my tumblers which may have been garbage. If you or someone else purchases this grit, which I highly recommend, I would love to hear what someone with more experience thinks about it. I am only positive that this grit is giving me better results in both my 2lb and 17lb tumblers in a 7 day period than the free grit was giving me in 10-14 days. At last the cheap 70 grit I am now using is from Harbor Freight Tools “CENTRAL PNEUMATIC 50 Lb. Black Aluminum Oxide 70 Grit Abrasive Media”.

[@elizabethlewis3509]

I'm flabergasted too. So glad you performed the experiment.

[@MichiganRocks]

Me too. I never expected that.

[@lizimpey6338]

Really pleased to have found you. I’m brand new to rockhounding and your channel has been outstanding in helping me learn about my new hobby, thank you and happy rockhounding 🎉🎉🎉

[@MichiganRocks]

You're welcome! I'm glad to help out.

[@AarynGulledge]

Very well planned and executed experiment that's quite relevant to the tumbling community! My guess/theory is that you basically have competition between grit breaking down rock and grit breaking down grit. Above 3 tbsp, the grit breaks down the grit faster than it breaks down the rock. I'd guess that if you did another set of experiments starting at 0.5tbsp and going up to 3, you'd see the rise you expected here, and then the weight loss plateaus like you observed here. I'm not saying you have to do this experiment, but it might help explain what's going on a little better. Great video!

[@MichiganRocks]

That's an interesting theory. I hadn't really thought of the grit breaking itself down. I should redo this with less grit, but I'm not planning to right now. I have a couple other experiments I want to try first.

[@KimBlowney]

I found your experiment very straight forward and informative. When your new to the hobby, reading to many opinions on how much grit to use can leave you confused on who to believe. Your video is the best I've seen.

[@MichiganRocks]

After reading all the comments on this video, I ended up doing another video on this topic. My results were a bit different, but I still decided to go with three tablespoons. kzbin.info/www/bejne/e4qwqJSibqdml5o

[@清志郎-きよしろう]

Hello. I started tumbling in January of this year based on your videos. However, your device and mine are different, so I created a form that is suitable for my method. Your video was helpful, thank you. My device Rotating tumbler: KT-6808, KT-245 (approximately 3 times the capacity of KT6808) Vibrating tumbler: SP-B10 (the capacity of KT-245 is just right) #60/90~#500(+borax) No media used In KT-6808, there were 3 large spoonfuls of undigested grid, so I used 2 spoonfuls after that. KT-245 is three times that. #1000, 3000 : using polishing media #Polishing :using polishing media, compound and borax I manage these items using EXCEL, including the equipment used, date, water volume, grid volume, etc. I'm looking forward to your future videos. From Japan

[@MichiganRocks]

It's good to keep records like that. It speeds up the learning process.

[@qaphqa]

I love this video. I love the mathematic set up and rigor. I am impressed by how information rich it is without being dense. I really appreciate how much insight you have given into the hobby of rock tumbling, valuable for spectators and enthusiasts alike. You really have the rock rizz.

[@MichiganRocks]

I'm glad you're so happy with my little video! Obviously, I'm learning stuff here too.

[@briancoulomb]

I would love to see more of these types of experiments. I also wonder if more or less water would have played a significant role. I also wonder about the polish stages. 6 tablespoons of polish seems like a lot but I’m following Lortones guidelines.

[@MichiganRocks]

I have a few more experiments planned. I hope to have the recording of the second part of this one done today. Then there are three others I have in mind.

[@briancoulomb]

@@MichiganRocksThat’s great to hear!

[@miltonthecat2240]

Thanks for doing this experiment! I have been going heavy on the first stage grit, too. Visualizing a graph of the results in my mind, my engineering experience is trying to tell me that . . . the grit might not be doing anything at all! It's conceivable that some tiny amount of grit is required to start the process, after which the slurry does the grinding. I just re-watched your 365-day tumble video, and it also hints that the grit may be doing less than than we think (since the silicon-carbide barrel rocks probably didn't lose the entire 27% of their weight in the first week of tumbling). And if the slurry is doing the grinding, then the type of rock being tumbled must be important. Does the subject rock break down into sharp or rounded particles? So a good future experiment might be to compare, say, two two-month tumbles, where one barrel is opened and restarted with fresh grit every week, and the second barrel is left alone. I certainly wouldn't mind skipping the clean-out step for a week or two if I knew that the rocks were still progressing without fresh grit.

[@MichiganRocks]

In that year long tumble, the rocks surely kept grinding after the first week, but I'd guess that grinding probably got less and less each week as the grit broke down into smaller and smaller particles. I'm imagining an exponential decay type of graph.

[@AgateAriel]

I love this!! I am so impressed by your dedication to detail on making sure each barrel was the same. I use only two tbsp of grit for my barrels or one tbsp per barrel pound. I totally agree that you need way less grit than is usually recommended!

[@MichiganRocks]

Are you saying that you have two pound barrels? Weighing each rock to make the barrels the same was the most time consuming part of this video. I have more experiments planned, and this is the part I look forward to the least.

[@775Rockhounding]

Thank you Rob! I’ve been tumbling for close to three years now and I am still learning great info from you. Your detailed videos are greatly appreciated.

[@MichiganRocks]

I've been tumbling for a dozen years and, as you can see, I'm still learning too.

[@jeremykay2261]

New to the hobby.. learning a lot from your videos.. I really appreciate your information, thank you!

[@MichiganRocks]

You're welcome!

[@markattardo]

Huh?!? I Surprising results! Very cool experiment.👍👍

[@LuckenbachTexas7499]

I use 3 tablespoons of grit for my 3lb drums and 10-12 tablespoons of grit for the Thumler's Model B. It's a home-run every time doing it this way.

[@kabbythedog9409]

That’s what I was looking for thanks I’ve never felt grit in mine but been ball parking it the whole time

[@EyesWideOpenPraiseYah]

I'm brand R new to rock tumbling. I did some research on different tumblers and went with lortone. Can't wait to jump into it with the kids and enjoy a new hobby. P.s. I love your channel.

[@MichiganRocks]

Lortone is a great choice.

[@davidhile5363]

Surprisingly results indeed. I guess it’s the old adage that more isn’t necessarily better. I’ve always used 3 tbs in a 3 lb barrel and I don’t try to reclaim unused grit. It seems like a waste of time. There’s been about 4 times in my tumbling career when I’ve opened a first stage grit barrel and most of the grit is still there and very little has been done to the rocks. I’ve always assumed that something caused the rocks to lock up as a unit and very little tumbling took place. I always appreciate the time and effort that you take in making these experiments. Awesome video Rob !

[@MichiganRocks]

Whenever that has happened to me, I think it has been because I had too many smalls in there. The small pieces were either small saw scraps or plastic pellets. When I first started, I used plastic in the first stage several times on material that I thought was prone to fracturing. That was a bad plan.

[@nonsequitor]

Great video! And yeah - I'm sure you're correct that excess grit ends up cushioning the impacts and at higher levels creating a layer on the rocks where it's grit on grit not grit on rock, essentially reducing abrasion. If you take it to the extreme for clarity, in a tumbler half full of grit the rocks would rarely ever touch, they'd just be rolling around in grit. As anyone who's been to a beach can attest: just a few grains of sand between clothes and skin causes painful abrasion but you can roll around with bare skin in sand just fine. Taking it to the other extreme: just one grain of grit in the tumbler would still scratch rocks but take many years to cover the whole surface.

[@MichiganRocks]

I love your comparison to beach sand. That makes your point very clear.

[@saralynn518]

I love a good old-fashioned experiment! The rocks are gorgeous.

[@evangelineburns7825]

Wow. My husband and I were also surprised at your results. Love your content.

[@timtalksaboutrocks....most6644]

It is really cool that you did this experiment and had the "grit" to report the results to everyone even though it didn't turn out the way you expected.:-)

[@MichiganRocks]

Gotta love a good pun!

[@danderth]

Nice test. I don't tumble rocks, but your interest in the results rubbed off on me.

[@MichiganRocks]

It's never tool late to start! I'm curious how you ended up watching this if you don't tumble, though. This doesn't seem like it would be the least bit interesting unless you were into this sort of thing.

[@danderth]

Content ain't King, Character is. I like rocks, but I like you better. Being subbed to you for years now, I've watched all your videos. Watching every video, regardless of content, is more about supporting you. But like you said, it's never too late to start rock tumbling; I would like to some day, so I also watch with a little future interest in mind.@@MichiganRocks

[@MichiganRocks]

@@danderth Well, gee, thanks!

[@JohnPhilpott-q5k]

Food for thought. I have appreciated your advice so much and so I’m sharing my experiences. I have had a nightmare trying to polish my obsidian. I finally broke the cardinal rule and just tossed them in with my jasper,agate and Chalcedon. They literally came out better than I could have ever imagined I’ve redone my old ones and they look great. I’m confused but happy.

[@MichiganRocks]

Huh, that's interesting. Was that in a rotary or a vibratory tumbler? What I think happened is this: Obsidian takes a really long time to tumble well. I think that's because it's a soft rock and doesn't break the grit down very quickly. Since the grit continues to be in larger pieces for a longer period of time, it leaves bigger scratches until the grit finally wears down. By mixing it with harder rocks, those harder rocks break the grit down quicker giving it a polish quicker.

[@JohnPhilpott-q5k]

@@MichiganRocks I use rotary until I’m happy with the super slick clean non pitted stage. And yes I use vibratory after that. But. I’ve gotten into the 18 lb machine. Obsidian alone just hammered it’s self and that’s with ceramic pellets and borax and grit. I simply tossed a few dinged obsidian pieces into a batch of regular (to me) rocks to fill the tub. I have learned from you to go longer than the typical recommended time. So 220 for two days. 500 for six days and then I ordered the great polish from the RockShed. And ran two mor days. Okay it’s amazing. I’m rerunning do much material. And the results are just insane. I also use this vibrio/18 to clean up raw material. Soap and water polishes this stuff in a way that is so impressive. I’m always learning

[@MichiganRocks]

@@JohnPhilpott-q5k I agree, it's fun learning new techniques and trying new things. Keep on experimenting!

[@tammycooper7312]

Thank you for this, I've been using 4 Tablespoons. This will save me some money.

[@MichiganRocks]

That's what I was hoping to do. Mission accomplished.

[@keithcunningham7925]

Wow very good experience when i tumble i always follow your steps and i get good results so thank you for doing this

[@MichiganRocks]

You're welcome, Keith.

[@nicolagraynewzealandrockho8976]

Excellent video. The only explanation I'd have for the barrel, is that the extra grit provided cushioning in the first few days of the tumble. Really interesting. I use too much grit.

[@MichiganRocks]

Hopefully this will save you some money on grit from now on.

[@nicolagraynewzealandrockho8976]

@@MichiganRocks sure will, I always follow your guidelines 😊

[@salliemorrill2671]

Very interesting results, & yes, I was also stunned. Seems to me your control was set w/in reason. Now I have inquire as to whether you have conducted a similar experiment w/polish or final stage of tumbling. Curious about that information. Hello to Nancy and Sam. God bless.

[@MichiganRocks]

With polish, it would be really hard to measure the results. Polish removes very little rock compared to the first stage. The only thing I could do is look at the rocks after to see if they looked about the same. It would be very subjective.

[@firechicken455adventures]

Very interesting results. Sometimes, we surprise ourselves with trying to understand what works best within our hobbies. Thanks for sharing 👍

[@weathertrainsrandomniss1083]

Very interesting! Great detail went into this test. Thank you. Cheers from the 920 of Wisconsin

[@MichiganRocks]

Due to a lot of follow up questions, I actually did more experiments after this and made a part two to the video. kzbin.info/www/bejne/e4qwqJSibqdml5o

[@FSCHW]

Thank you. I think it shows that manufacturer recommendations may be best.

[@MichiganRocks]

But Lortone recommends four tablespoons. Three was about the same, so why use more than necessary?

[@FSCHW]

@@MichiganRocks I have a thumlers and it says 1 per lb. I didn’t realize Lori tone said 4 for 3. Maybe it should be on the MHOs scale, something like 8=4 tbsp 6-7= 3 tbsp 3-5= 2 tbsp

[@timmyfingaz100]

LOVE how you tried to keep everything the same, down to the weight of the rocks! This channel is a wealth of knowledge! I've wondered myself recently if the amount of water is critical to grinding/polishing efficiency too. I'm very new to polishing rocks, finished one small batch with a nice glossy finish (not perfect but shiny for my 1st attempt). Did the same process with the last batch but they didn't take the shine like the others, the water/cerium oxide slurry mix was not thick at all and guessed that was why. I understand it should be thick almost like a paste. I've got them back on now with slightly less water and gave them another scrub, I've been scrubbing with ivory soap in between stages and keeping things very clean, not to cross contaminate grits.

[@MichiganRocks]

I plan to test water amount in a future experiment. I can tell you that the slurry definitely does not have to be thick like paste. Most of my slurries are pretty watery but I have a lot of rock dust after I dry out my slurry to dump in the garbage.

[@lilalightandlove421]

Super video! I have always wondered if I should’ve added more grit and now thanks to you, I know! Rob, you’re the best!

[@MichiganRocks]

Glad to help. I always wondered too.

[@JR-vi4rl]

👏 Well done experiment. I've been using 2-1/2 tablespoons of 60/90. I think your logic of there is only so much contact area between the rocks so having more grit won't make a difference is valid. If a person goes two weeks instead of one between rinsing, maybe more grit is better. I prefer one week so I can inspect to see if any are ready for stage 2.

[@MichiganRocks]

I agree with what you said about running them for two weeks. More grit might be better. But like you, I like to get any rocks that are finished out of the tumbler as quickly as I can so they don't get any smaller than necessary.

[@geneplumley4136]

Great video! There is no better feeling than being surprised when your hypothesis is completely wrong. I love the scientific method. Everything was really well thought out. I have to say, though, I would really like to see if 1 or 2 tablespoons would yield similar results. Then the ratio you were looking to diplay would become beneficial. It won't cut down on tumbling time but definatly can prove potential cost savings in grit. You have great content. I can only imagine how much time and money I saved getting into this hobby by first watching your videos.

[@MichiganRocks]

I wish I had included two tablespoons in my experiment. Even at the best ratio of grit to amount of material removed, I might still use more grit if more grinding happened. You also have to consider time and electricity. I'd be willing to be a little less efficient with my grit to get faster results.

[@briandavenport798]

I think an interesting 2nd experiment here would be a barrel with no grit at all. How much does the grit actually contribute to grinding action? Is it the rocks colliding against each other or is it the grit in-between? Nice work Rob!

[@MichiganRocks]

In that case, you will like this video: kzbin.info/www/bejne/qJyUdXinrq1rhsU

[@main_frame]

Michigan Rocks Rocks!! Thanks for all the helpful info from a rock hound and now tumbler in PA

[@MichiganRocks]

You're welcome!

[@LTGuitar51]

Great experiment and good results. I have been using 3Tbl and I’m glad to know it’s a good amount. Thank you, I bet it was fun and educational to be a student in your classes!

[@MichiganRocks]

I think that depends on who you asked. Some kids loved me, others did not. You can't please everyone!

[@KristenDilligaf]

Dude!! You're crazy precise with measuring the rocks in each barrel!!! I applaud you on that though! Do it right or don't do it at all!!

[@MichiganRocks]

That seemed important, so I did it.

[@KristenDilligaf]

@MichiganRocks Oh, for sure! I bet it is super important. It helps to have the right amount of everything. There's a science behind it! I've been trying to read up on how to get the best tumbles. Do you have any suggestions for a first-time tumbler?

[@MichiganRocks]

@@KristenDilligaf Sure, watch my videos! Here are. a few. Just pick the one that most closely matches what you have to work with. The second one is probably the best for most people. Rotary tumbler followed by vibratory tumbler: kzbin.info/www/bejne/nquVdmOuf754jbs Rotary tumbler with ceramics: kzbin.info/www/bejne/moqqd5SiZcpkjbs Rotary tumbler with plastic pellets: kzbin.info/www/bejne/e5-xp6ytrN-nqJo How to use a Nat Geo Tumbler: kzbin.info/www/bejne/eaS3lGShjbqohtE Tumbling beach rocks in a Nat Geo tumbler: kzbin.info/www/bejne/lYfQnmVqe8hqoJY Also watch this: Why aren’t my rocks getting shiny? kzbin.info/www/bejne/iKazpaOqp5ySjJY There are more, but that's plenty to start out with.

[@teresaradford4467]

Love the video and all of the comments with interesting theories. Thank you so much for creating so many informative videos.

[@MichiganRocks]

Your'e welcome, Teresa.

[@greatnorthernviews3052]

I tried doing some of that with mixed results. Nice share Rob!😊

[@brianholcomb940]

What an intriguing experiment! I thought like you, the more grit, the less rocks! Very confusing and informative at the same time! Thanks for sharing!

[@MichiganRocks]

Hopefully we're all learning here. I know I am.

[@derwood773]

Please do more experiments! These are my favorite of your videos. The one where you did sand vs water was so informative. See you do this one again Water vs 1 tbsp vs 2 tbsp

[@MichiganRocks]

I have a couple more experiments planned.

[@derwood773]

@@MichiganRocks That's so exciting! 😀

[@KristenDilligaf]

Love that you're rocking the Michigan University shirts, too! My boss, Raymond Greene went there to be an Optometrist!! Lol back in like the 80s though. You definitely look younger than him 😂😋

[@MichiganRocks]

I was there in the late 80's. Graduated in '90.

[@kna60]

Hi, interesting experiment, thank you. I think your explanation is good. Perhaps we also need to consider the distribution of abarasion forces between the grains. The more grains there are between two rocks, the lower the stress on each grain and the lower the abrasion at that point.

[@MichiganRocks]

Yes, I like that theory. I pinned Jonathan's comment that said the same thing. It's the best theory I've heard.

[@geoffjohnson6555]

Wow! Didn’t expect that one! Great video Rob!

[@MichiganRocks]

Me either!

[@davidsommerfeld2955]

New to lapidary and rock tumbling, about 8 months. I enjoy your videos and have learned a lot, thanks. Also thanks for doing this test. I have 2, 6 lb and 1, 12 lb Lortone tumblers. I also have 10 and 18 lb Thumler style vibratory polishers and this week I picked up a used UV-45 tumbler. All of my rock gets the first round in the rotary tumbler. For the 6 lb drums I have used between 3 and 6 Tsp of abrasive with equal results. The 12 lb drum has been 7-10 Tsp abrasive with equal results. Always tumble for a week. Early on I started adding Borax to all stages and I think it helps keep the abrasive in suspension and cutting better. It’s a cheap additive and I’ve always used it. My test on abrasive efficiency is to rinse the slurry after clean out and see how much grit I can detect. A white bucket will tell you how much or little is left after tumbling. All of my polishing after the coarse grit has been in the vibratory polishers. I feel I get a superior finish and I can cut the total polish time to a quarter to a third of the time of doing all stages in a rotary tumbler. Thanks again for sharing your knowledge and experience working and polishing rocks.

[@MichiganRocks]

I also do almost all of my finishing in a vibratory tumbler. I bought one before my first batch was done, so I have very little experience finishing rocks in a rotary tumbler. Have you weighed your rocks after tumbling? It sounds like you're just checking to see if your grit has all been used up. When you say you had equal results with twice as much grit, are you just looking at the left over grit, or are you weighing the rocks to see how much was ground away? Also are your measurements in tablespoons or teaspoons? Tsp is the abbreviation for teaspoons, right? I was measuring in tablespoons.

[@davidsommerfeld2955]

@@MichiganRocks I stand corrected, I use tablespoons for measuring. I’ve never weighed my rocks throughout the tumbling process. Another KZbinr suggested checking the slurry for grit to see if there was excess after the tumble and that’s my indicator if I’m using enough or too much. I’m not a stickler for perfectly rounded stones, I often prefer the natural way I found it polish. I finish with 2 sizes of ceramic media to get into all of the nooks and crannies. I’ve done some large 3-4 pound Mexican crazy lace agates start to finish in the rotary tumbler with good results. I’m doing palm stone size pieces in the vibratory tumbler with excellent results. I’ve got some 4-5 inch pieces ready for the Thumler UV-45. My goal is to tumble and polish pieces in the 5-10 pound category. I’ve seen others do this with good results. Finding an affordable drum big enough is the challenge for this project.

[@MichiganRocks]

@@davidsommerfeld2955 I haven't done too many larger tumbles, but I've done a couple. I think large tumbles are awesome though.

[@davidsommerfeld2955]

I appreciate your thoughts and comments. As always, KZbin is a wealth of knowledge for beginner rock hounds. The largest single tumble I’ve seen was a stunning piece of Mexican crazy lace agate that weighed 45 pounds if I remember correctly. The guy used a 65 quart tumbler and it took 6 weeks to finish. This gave me motivation to try it on a smaller scale in the 5-10 pound range. Having been a machinist in the past and a brother that has a machine shop, my mind is full of ideas to fabricate equipment to pull this off.

[@MichiganRocks]

@@davidsommerfeld2955 I don't think it was quite that big, but I think I know exactly what video you're referring to. There's a tennis ball next to the rock in the thumbnail.

[@julieshipp8077]

Wow, that was not the results i was expecting either. I think about the time you put in to the details of this by finding the similar weight rocks for each barrel. Not an easy task. Good information to know now when using my small barrels. Thank you for sharing!

[@MichiganRocks]

Yeah, that took awhile. I have always wondered about this, so I learned something too.

[@Algorhythmz]

Very interesting results! Thanks for helping us learn and sharing your experiments, Rob. This was a great episode, fun learning experience.

[@MichiganRocks]

You're welcome!

[@shewearsfunnyhat]

The old timers in the rock club I belong to say to use one tablespoon for the three pound barrel. Thats what I have been using in my first batch. I dont know if its enough but I am happy with the results so far. I will probably repeat the stage 1 at least twice in my second batch. I only have a single Lorton 3A.

[@MichiganRocks]

I did a part two of this video that you might find interesting too. kzbin.info/www/bejne/e4qwqJSibqdml5o

[@shewearsfunnyhat]

@@MichiganRocks thank you

[@trbowlin]

Great experiment. I think what you ran into is a viscosity problem. You used excellent experimental design, holding all factors constant, but the viscosity of the water and grit solution probably changed significantly. Viscosity increased as you increased the concentration of grit. A more viscous solution will grind rocks slower because the velocity of the solution moving in the drum decreases because of the increase in viscosity. The friction thing is also pertinent in as much that as you increased the concentration of grit, there was significantly more friction (more viscosity created) between the grains of grit in the solution, again slowing the velocity of the tumbling solution in the drum. There was no detectable difference in the amount of grit present at the end because the grit ground itself as well as the rocks. Just a thought.

[@MichiganRocks]

Thanks for your theories. I never really thought about grit grinding against itself until you and others pointed that out as a possibility. I'm not sure about your viscosity theory, though. There are people who add various things to their barrels specifically to create a thicker slurry. The most common things I've heard of are old slurry and clay, sometimes in the form of kitty litter. There is also a product called "Old Miser" that is a slurry thickener. The idea behind thickening the slurry is to make the grit stick to the rocks better. The grit can only work if it's between two rocks, not if it's setting on the bottom of the barrel.

[@jennifervh4434]

Thanks Rob!! Would Love to see your favorite cold weather hunting gear. Might be a good vid idea!

[@MichiganRocks]

I don't think that would be enough for a video. I don't do anything too interesting. I wear neoprene decoy gloves, which might be the only thing that's unique. I have the ones I wear listed in my Amazon storefront, which you can find in the description of this video.

[@semiproactive9625]

I was curious if the grit was 100% consumable, or if there was ever enough left to strain it and reuse? We all voted here for 3 Tbs going forward. Happy Friday in the mitten. Thanks, Rob.

[@MichiganRocks]

No, it's not reusable. By the end of the week I should be all used up.

[@staceymcmahan5016]

This is a great experiment ! I would have thought the same so that was a surprise to me too. I'm still learning doing the research on the products used and what the best ones are. I guess it's personal preference. With you experience in sure you've experimental with many products . I really enjoyed this and enjoy all your videos . Thank you! 😊

[@MichiganRocks]

I probably haven't experimented with as many as you might think. I did a lot of reading before I started and found good suppliers right away. Since I liked the products I started with, I have just kept using them. There are a few that I have changed, but not many.

[@TheRogueRockhound]

If you had a lab scale, you could weigh the grit and plot it all out on a graph. You could create a sweet material/grit ratio list

[@nhrockaholic6038]

Very interesting if not totally confounding. Thanks for the video.

[@MichiganRocks]

You're welcome. Even if I don't know exactly what's going on, I'm glad to only use three tablespoons.

[@DecorAgate]

Thank you for sharing very good and useful experiments

[@Nikkisavage100]

Hi Rob, Thanks for the help

[@milesnn]

Awesome awesome thanks for taking the time. To do this and share it

[@MichiganRocks]

You're welcome.

[@francoiselandriault8164]

I really appreciated that video. It was very informative and well presented. Thank you for sharing your experiences and knowledge. I love to learn.

[@MichiganRocks]

Thanks, I'm glad you found it interesting too!

[@wepri679]

I REALLY hope you do another video trying another test going the other direction (less, not more) grit to see if people can save on grit by using less than the recommended one tablespoon per pound. I recommend doing another 4-barrel test with 3T (control), 2T, 1T, and 1/2T.

[@MichiganRocks]

I told a bunch of people that I wasn't planning to do that but now I'm thinking about it. I think I'll do 1, 2, 3, 4 to get a little more overlap with the previous test. Going less than one just doesn't seem necessary. One tablespoon is not that much.

[@wepri679]

@@MichiganRocks that's great! I look forward to seeing the results if you do take this on! I appreciate the effort that goes into the preparation.

[@sboydrocks9412]

Great experiment professor Rob. You do the hard work so we don't have to. Seeing as I have only one tumbler and only one barrel. You saved me at least 5 weeks. Thanks and I would watch any future experiments you might do. 😀

[@MichiganRocks]

Yeah, it's easier when you have a bunch of barrels. I'm glad to have saved you a little time!

[@cinciao5692]

As always, great video with helpful information for all of us! I do commend you on these experiments and performing them objectively! 😀

[@MichiganRocks]

Thanks!

[@roman11469]

Great experiment! I was surprised by the results too.

[@I_wish_I_knew_something]

Cool video, very informative. Fun experiment. I agree with you, fine balance of water, surface area and grit. I’m thinking once the grit gets suspended in the slurry it gets less effective.

[@MichiganRocks]

I think the opposite is true. I think having the grit suspended in the slurry is necessary for it to be effective. If the grit sets at the bottom of the barrel, it's not going to do much good. What you want is the grit between the rocks and getting suspended in the slurry is how it's going to get there.

[@I_wish_I_knew_something]

😂Let’s agree to disagree 😂 Just kidding! You’re very smart at this and are highly knowledgeable. I’m pretty much, “Rocks are pretty.” grey rock are my favorite. :) i have had grit stuck in the corners of my bucket before.

[@SirNomad]

I was given a Thumler's UV-18 (Industrial) with the appropriate rock approved bowl. I'd LOVE to see a video on tumbling with one of these or similar! I have no idea how much grit to use! I do remember you using a spray bottle to get all the rocks appropriately dampened though.

[@MichiganRocks]

I don't have a tumbler like that, but I do have a Lot-O vibratory tumbler. You could watch my video on that as a starting point. kzbin.info/www/bejne/nquVdmOuf754jbs I'd also suggest getting on the Rock Tumbling Hobby forums and asking for some advice there. There will be several people who use that exact tumbler and will be very willing to help you out. You could also just read some old posts and get the information that way. There should be lots of old posts on that very popular tumbler. forum.rocktumblinghobby.com

[@cassandrasweetnich9333]

Fascinating! Great experiment.

[@mitchgillilan]

Thanks for putting in all that work! I love the variables you used and how accurate you were with sizes and weights. I'm sure lortone has done some lab work on this and come up with similar numbers too? Maybe 🤔 I didn't know most the grit breaks down in 7 days. I figured it was longer.

[@MichiganRocks]

I'm not sure how they got their numbers. It would hope that they had done something similar.

[@Thracium]

Thanks for sharing all this valuable info!

[@emmikate]

This makes so much sense because the only part of your method I do not follow is the amount of grit. I always use less so this doesn't surprise me this just makes me feel a little less crazy because I thought I was going rogue. Lol how this must sound to people who don't care about rocks.

[@emmikate]

Depending on the rock I will say you can absolutely get away with two because that's about what I use and I find if I use too much more there's so much grit left over for me

[@MichiganRocks]

I wish I had tried two tablespoons in this experiment, but I didn't. At some point too little grit as to decrease the amount of grinding that takes place, but how little is too little? I'm surprised that you have grit left over though. That rarely happens to me. When it does, it's because I have put in a bunch of small saw scraps. Adding plastic or ceramic media in the first stage will cause that too.

[@emmikate]

@@MichiganRocks I think that's part of it because I have been really trying to do smaller rocks and trying to figure out what the balance is If I wanted to rock small enough to turn into beads.

[@emmikate]

@@MichiganRocks Also I would say any less probably would be too less because I think I did try less before and it didn't do much. That might be fun do three one that's 3 tablespoons ones that's 2.5 and one that's 2 🥰 but yeah I'm not sure I'm going to be able to do my batches of Little Rock's only like I want to.

[@ShaneHoffa]

Love your channel! Would you ever consider making a video about how you created your custom tumbler cabinet? That thing looks fantastic!

[@MichiganRocks]

I made a couple videos when I first started making videos a few years ago. My friend designed it and asked me not to share the plans, but the videos show it pretty well. Homemade Tumbler: kzbin.info/www/bejne/bKKslH5oj9Sbfa8 Tumbler Update: kzbin.info/www/bejne/hnKwgHaZZ6eBgK8

[@ShaneHoffa]

@@MichiganRocks amazing! Thank you!

[@MileHighDriverGuy]

Thank you, Rob! This was extremely helpful!

[@MichiganRocks]

You're welcome!

[@colesonafrank5329]

Great video as usual! I really enjoy your stuff and have found your suggestions very useful. Thanks! I'm no statistician, but I do remember that single sample test results aren't reliable and don't give you any idea of what your margin of error is. In my own experimental work the way this hit home the hardest was probably accidentally "discovering" (what any lab procedure text would have reminded me) that even just weighing stuff has a rather appalling seeming degree of error such that multiple weighings (whether on multiple scales or not) need to be made to get (statistically useful) accurate averaged weights. So unless you run this same experiment, or at least the two extremes, multiple times (sorry I don't have any recollection of the minimum or optimal number, but probably upwards of 4 or 5) the differences you see in your results are likely to be within the margin of error. So, don't try to hard to "make sense" of this particular (pardon the pun) apparent result;)

[@MichiganRocks]

I realize that more trials would have to be done to make this a really reliable experiment. But for me, it's enough to convince me not to use huge amounts of grit. I'd do more trials, but it just takes so much time to weight all those rocks.

[@ruthchapman3847]

Fascinating, thanks, I will use this in the future.

[@MichiganRocks]

You're welcome!

[@bakeblaker01]

I like it when you do stuff like this. Another interesting thing to try would be the time to no grit. What about 6 days with 3 tbls ? Is there still grit after 5 days? If it’s gone after 5 days, is there a worthwhile benefit to go the extra 2 days with just the slurry? Or could total tumble time be reduced by a lot by saving that extra time every tumble. Or maybe it just isn’t worth it to try and remember what day to check, as the whole checking every Sunday seems like a good plan to remember.

[@MichiganRocks]

The grit breaks down over time, so each day there's going to be a little less grinding. You could take them out earlier and replace the grit and get done quicker. Or you could let them go longer and get a little more out of your grit. I think seven days for a tumbler going at the speed of mine is about right. The National Geographic tumbler is much faster and I think for that, four days or so is enough.

[@tanyawinters3979]

Our house’s previous owner used crushed marble & I tumble it in my Nat Geo with no grit for 3 days and it does nice.

[@MichiganRocks]

That's interesting. Marble is pretty soft though, so I can see the rough edges being chipped off pretty well in such a fast tumbler.

[@1JawsJr]

Now, that you have figured out the volume of the rocks lost in the initial course grit, it would have been nice to see if there were any issues with quality. I know you ran them once prior to starting this experiment, however, seeing them up close to see if there was a quality different would have been nice. To me, it is all about quality of the tumbled stone when it is done with the cycle, not about how much I can get done per cycle.

[@MichiganRocks]

This is only the first stage, so the whole point is to grind as much rock as possible. It's the later stages where the quality matters. I did look at all the rocks to decide which ones that were done with the first stage. I didn't notice any difference in the quality at all.

[@kduncan9533]

You make amazing and informative videos. I love the beautiful rocks you find and the tutorials on cutting, making jewelry and your experiments! I was just wondering today if the manufacturer recommended grit is really necessary. Think I will give 3 TBS a try. I am very interested in your cabinet full of tumblers. Did you make it yourself? Do the motors running the tumblers get hot? I run a small fan near my tumbler motors to keep them cooler. Have you made a video showing how you set up the tumbling mechanisms? Would love to see more! Thanks again for your awesome videos.

[@MichiganRocks]

That big tumbler was designed by a friend of mine and I built it. The motor does get hot, which is why it's on top rather than inside the cabinet. That has been running pretty much nonstop for several years with no motor problems. Here are a couple more videos showing the tumbler in more detail: Homemade Tumbler: kzbin.info/www/bejne/bKKslH5oj9Sbfa8 Tumbler Update: kzbin.info/www/bejne/hnKwgHaZZ6eBgK8

[@kduncan9533]

Thank you for the information and links. We will explore this, nice set up and pretty quiet. I have 2 Loretone 33b and they are surprisingly quiet, but I love your set up!

[@robbybobby64]

I’ve always used 3 in my 3 lb. Who knew it would be optimal. Thanks for confirming. Could it be like a balloon won’t pop if pressed against many nails spaced closely. Push it against one nail and it will. Maybe the grit is doing the same thing to the stones? Too much grit to get a good grind? Crazy results I agree.

[@MichiganRocks]

My friend Jonathan had the same theory. I let him watch the video early and asked him to put his thoughts in a comment. I pinned it to the top. I think you both have the right idea.

[@davechittenden1657]

He grindeth slow but exceeding fine!

[@11stefanj]

Thanks Rob. I act Actually only use 1 tablespoon and run for 2 weeks. I used to use 3 but always have grit left over so for me it works best

[@MichiganRocks]

That's interesting. I almost never have grit left over. The exception is if I put too many really small rocks in the barrel. That almost always results in left over grit.

[@11stefanj]

Only difference I can see is I use Thumler's barrels. Even on my larger barrels (12 and 15 Lb) it is 1 teaspoon per pound. I keep wanting to purchase a Lortone Machine just to see if the barrels make a difference lol@@MichiganRocks

[@MichiganRocks]

@@11stefanj I have a small Thumler's tumbler and I didn't notice a difference in the way the barrels work. I just notice that the lids wear out really quickly on those little Thumler's tumblers.

[@11stefanj]

Yes they do. I repair them with plexi and the repairs last years! I am going to have to revisit my grit amounts now. You really got me thinking here. @@MichiganRocks

[@bobmayr1066]

It’s been many years since I tumbled rock. I remember when I did I was a bit thrifty ( some said cheap) . I tried tumbling the first stage with no grit for about one week. As I recall it did round them down some. Think of rocks on a beach. Just rock and water.

[@MichiganRocks]

I did that too. kzbin.info/www/bejne/qJyUdXinrq1rhsU

[@geoffyoung4548]

I would be very interested to see the results of repeating the experiment with 1 & 2 spoons of grit. I think we were all surprised with those results, maybe we could be in for an even bigger surprise!

[@MichiganRocks]

I have that video made, but I'm waiting a bit to release it. I have a couple more videos from my southern trip to show first.

[@chrismothy481]

When im doing my cleanouts, i have 4 buckets that i rinse into. One for each stage. I pretty much always have at least a little unused grit and dont want to waste any, so i pour off the water and the unused grit stays on the bottom of the bucket and i reuse that. Itd be interesting to see how much grit you have leftover in an experiment like this. Rinse into containers, pour off the water and the lighter used grit, and measure whats unused. Id say its probably valuable information I will say that ive only done this for stage 1. Ive kept the used grits for other stages, but havent tested if it will work in the tumbler Eventually i want to test if the polish can be reused with decent results, or used in addition to fresh polish in some way But this way, i can put a bunch of grit in (if i want to) and i dont have to worry about wasting any. I figure that with 2 or 3 tbsp, youre not getting as much grinding action after day 4, 5, 6... most of the grinding action will happen in the first few days. And stage 1 can take FOREVER so i try to speed it up as much as i can

[@MichiganRocks]

I can't imagine how much time that would take to reclaim that grit. How do you separate the grit from the ground up rock? After a few clean outs, if I dump the water off my bucket, I have several inches of rock sludge in the bottom of the bucket. I haven't done this myself, but I have read that polish is the only grit that can be reused. Of course if you have actually gritty grit left, it can be reused, but if it's all broken down, then it's not going to be very effective. Polish on the other hand only improves as it gets more fine. I almost always finish my rocks in a Lot-O vibratory tumbler though, and that only uses 1/2 teaspoon of polish, so it doesn't make any sense to try to save it.

[@chrismothy481]

@MichiganRocks I don't really do anything special, if anything I just spray water into the grit bucket allowing the water to mix everything up. The unused grit sinks immediately and the finer ground up grit is suspended in the water which I can then dump off. As for the ground up rock, I havent noticed any. But I would probably only reuse the grit for a harder rock like agate to avoid any issues

[@annamayfield9920]

Great video! I have been having a hard time getting my rocks done for the later stages of tumbling. I have found myself that 4 tablespoons of 36/70 in a 3 pound barrel is too much even after one week. I want to ask a question though. Will you ever do a review of the Minisonic 4 pound vibratory tumbler? Please do a review if possible. I have had a rough time trying to get a hold of the Lot-o. I love your videos so much they have helped me come a long way. I went from using a National Geographic tumbler with horrible results, to a batch of rocks with an amazing polish and having 18 pounds of tumbling power! I hope you have a great day!

[@MichiganRocks]

I wanted to do a review of that exact tumbler last winter. I wrote the company and asked them to give me one to review, but they never answered me. I have plenty of tumblers, so I'm not really interested in buying a fairly expensive tumbler that I don't need.

[@therandomman4441]

I've applied this to all stages and it is perfect 2 scoops at 2 weeks in a 3 pound

[@MichiganRocks]

You mean you've done this same experiment for all stages?

[@Ylee999]

Very good test, however, since you have found 3 is the best, you should try 2.5 and 2, to see what happens.

[@MichiganRocks]

Here you go: kzbin.info/www/bejne/e4qwqJSibqdml5o

[@Kötkylä]

Very good video 👍 i been use 4tbsp, sometimes 3. I think i go back to 3 😄👍

[@MichiganRocks]

I have always felt like I was being a little cheap with three, but I'm going to continue to be cheap!

[@Kötkylä]

@@MichiganRocks its good way to be cheap i think 👍

[@jasonbedsole7110]

I usually use 1.5 to 2 tbsp. in my 3 lb. barrels and it works just fine.

[@RichsOutdoorAdventures]

Excellent experiment. Thank you

[@MichiganRocks]

You're welcome, Rich.

[@JeffWeymier]

Great experiment.

[@BlueSteelRabbit]

Yay I love these informational videos.

[@Ally-Oop]

In terms of surface area what about chopping identical shapes, like cubes or rectangular prisms or flat discs, out of a single donor slab? Like if the samples are all from the same slab and with the same rough edge from a cutting tool that might cut down on the contact points while tumbling or hardness variations. Either way, entertaining video as always, thanks and kudos!

[@MichiganRocks]

That's an interesting idea, but would be very time consuming and also difficult to find one rock that would be big enough to fill all the barrels. The regular shapes might not move around the same as randomly shaped rocks would.

[@mattmoore4661]

Well done.

[@TyOtis]

Great experiment!