There are lots of reasons to delve into the realm of bucket spinning. If a bucket is broadly defined as most any kind of "container" then rotating buckets are found everywhere. They can mix, polish, grind, pulverize, cast, clean, tumble, stratify, and separate.
This Instructable is about how a few of them are constructed, and how they can be incorporated into STEM projects..
Check out the video at the top of the page. This particular rendition is a 3 dimensional bucket spinner - it can spin on any of the 3 axes, X, Y, Z. The cool part is that it only has mechanical ability to rotate in 2 directions but because of concurrent action it will rotate around all 3 axes, at the same time.
Which direction is it spinning - clockwise or counter-clockwise? This is one of the great questions in science. We know that this is a profound science question because the answer to the question is the same answer as for most other great science questions. And the answer is: "Well, it sorta depends...".
By carefully watching the video you can see that the bucket is always going in the same direction. Which is clockwise. Except when it's going counter-clockwise.
What would happen if you were inside the bucket? Would you think you were always spinning in the same direction?
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Step 1: First, a Little Context
This is a story of how a 3 day STEM project turned into a semester long activity. Bucket Spinning? 40 different methods? It was decided that the two instructors in an Alaska STEM program (both males) were far too oriented toward projects attractive mostly to boys. The solution, in the view of the administration, was to hire an additional instructor, a female, to bring some balance and refinement to the program. She was to expand the program into resin casting, jewelry making, arduino coding, baking, things like that - skills that might appeal to a wider audience - subjects in which the two current staff guys (old school, former shop teachers) were pretty much clueless.
Easter was fast approaching. The new teacher's first project proposal was a large Easter Rabbit Egg, cast in custom chocolate. Each student would finish with a humongous homemade chunk of chocolate to take home.. Several students immediately signed up, all girls. Several of the boys decided that since lots of girls were going to be involved it would be cool to also participate.
Unfortunately, so many eggs called for a stunning amount of fairly expensive chocolate. Turned out the size of all the eggs would exceed the size of the project budget. Sooooo, the new resourceful teacher announced that all the project eggs would be hollow. Two teams were formed - Group1 was in charge of producing the best recipe for homemade chocolate (designed to harden at room temperature) and Group2 to figure out how to hollow-cast a very large rabbit egg shell. The gadget video at the top of the page was the product of Group2. Their spec was to make a tool that would spin an object in all three dimensions at the same time, slowly, evenly - in this case, a bucket, and anything that was in the bucket. The rotation was to be slow and smooth - something that would keep a mass of warm chocolate continually coating the inside of a mold until the chocolate cooled and hardened.
Folks in Group2 were quite pleased with how their part of the project turned out. They were also pleased with Group1's results, because everyone received a large amount of good chocolate. Discussion started on what else their gadget might be used for.
The entire project team had worked well together. The administration was pleased with how things were going and suggested the STEM staff extend the project. New bucket duties were assigned.
Thus was the beginning of the Alaska STEM School Bucket Spinning Art Form. One of the first tasks for the team was to list out all the reasons they could think of that would justify investigation into the bucket spinning problem. It was kind of a "solution in search of a problem" thing. Then secondly they were to see how creative they could get in providing solutions.
The students found spinning buckets everywhere. Polishing rocks, mixing ingredients, deburring parts, stirring paint, casting resin, baking bread, making soap, grinding grain, pulverizing chemicals, etc, etc. Lots of uses also for devices that didn't just spin but also included centrifugal force. Industrial uses included production in pharmaceutical, cosmetic, baking, paint, detergent, textile, paper, food, metal parts, ammo reloading, etc.
Step 2: Design and Function
Because there seemed to be such a large and varied user base for spinning buckets, a custom machine with a single specific function didn't seem appropriate. A decision was made to create something like a Bucket Spinning Construction Kit, to be as flexible and generic as possible.
Through a long evolutionary process, the design for the Kits settled onto something similar to an outer metal frame and an optional inner frame. The frames were fixed to pillars on each side and allowed to rotate. Mounts were made for an arbitrary number of arbitrarily shaped containers. These containers could be placed in the center of the frame, or instead mounted around the peripheral to orbit around the center rather than simply rotate in the middle. Devices could be manually operated or motor driven, or both.
Step 3: Construction Intro
Instead of trying to generate creativity by limiting the Kit Parts Inventory, the STEM staff wanted to see what would happen if the students were smothered with options. Would they become "paralyzed with choices"?
Parts were to be off-the-shelf, and inexpensive. A field trip was taken to two local hardware stores -- Home Depot and Lowe's. Inventory for the student Kits would consist of whatever they could find in the plumbing dept of each store. Permission from store staff allowed the students to engage in hands-on hardware purpose and interplay, which eventually resulted in a Project Parts List. The list had to be approved by the STEM instructors for suitability and budget. The plan evolved into allowing variances for parts from other depts in the store, and territory expanded into Amazon as well as Lowes and HD. Amazon expansion was a good call - although not possible to physically examine parts beforehand, the exhaustive nature of choices and options was a big win.
Step 4: Trials and Tribulations
Here's a picture of an early attempt, made from copper pipe. It was a complete disaster. Seems that soldering pipe can be quite a challenge for amateur plumbers, and the need to frequently alter and test the design meant that any time a joint was altered the necessary heat would cause all the adjacent joints to also come apart. It was a great physics lesson in heat transfer, but the results were almost always a mess.
There were lots of failures. Everyone thought, for several reasons, that any genuinely useful gadget resulting from Kit construction should be metal. Nonetheless, PVC pipe and fittings were often considered because of cost and ease of construction. PVC was simply much easier to work with. Cheaper, too. Because there was a PVC equivalent for most everything available with metal pipe, a decision was made to add a Prototype Stage to the design process, done in plastic, using the last stage to finally convert everything to cast iron pipe.
Step 5: Bearing Installation
Kit construction was pretty much a simple task of screwing parts together. The only parts that took genuine forethought and prep were the fittings that required installation of internal bearings.
The two pictures above show how it was done for both PVC and metal. All parts had already been standardized around 1/2" pipe. Type 608 bearings, the kind found in roller blades, skateboards, etc. would almost fit inside the PVC fittings. Through trial and error one of the fathers of a student discovered that when the outer edge of a PVC fitting rested in 1/4" of cooking oil (around 300 F) for a few seconds, the would easily expand when firmly pressed onto a bearing. After the plastic cooled it shrank a bit and formed a snug fit. Worked beautifully. Because the hole in a 608 bearing is for an 8mm axle, all the connectors/fasteners (nuts, bolts, washers, etc) were standardized on 5/16" hardware.
For metal fittings a standard 1/2" copper coupling (about 1.5" long) can be inserted into each side of an iron pipe. The copper coupling is designed to fit over a 1/2" pipe - turns out the inner dimension of the coupling provides an exact fit for 5/8" bolts. And that same coupling will also fit inside the hole in a 1/2" iron fitting. Well, sorta. The threads in the metal fitting are tapered - the coupling will only slide into the threaded hole about 1/4". But by gripping and twisting the coupling with pliers the iron threads can be used as sort of a die as the copper part is twisted. Incredibly Convenient. You now have a plug to go into any iron hole to act as a copper bushing for 5/8" bolts. Just as PVC parts were standardized around 5/16" hardware, all the iron parts were made to work with 5/8" connectors.
See the pictures above to hopefully make sense of what is described.
Step 6: Putting It All Together
The Kit Construction Design is intentionally vague about some of the details. For instance, the possible number, size, type, and kind of container ("bucket"), and mounts for it, are endless, and are left to the discretion of the maker. Because all the uses described so far are designed to spin at slow speed, most anything can be used to hold the containers in place - wire, clamps, cord, even masking tape. How sophisticated to make the mount usually depends on the application - is it a one-off use, something to temporarily hold a container once for a short spin (mixing a jar of homemade trail mix?), or maybe something more permanent, to easily be mounted, opened, remounted (polishing rocks?). In fact, a permanently mounted bucket can itself be used as a holder for whatever is temporarily placed inside the bucket. A rock polisher can mount a tumbler for all 4 polishing stages at the same time and use an exchange system to produce a continual supply of stones.
The first video at the top of the page shows a simple tumbler. It's an overly complicated way to tumble, but it works pretty well.
A mistake in clamp design helped to accidentally discover an enhancement in tumbling use, shown in the 2nd video. By tilting the bucket 30-45 degrees, the twist of rotation also causes the material inside to slouch back and forth, producing significant increase in mixing/abrasion.
Step 7: One of the Finished Variations, Made in Metal
Time to watch the 2nd video at the top of this Instructable. This is the beginning of an attempt to build a powerful Planetary Centrifugal Ball Mill. Such a mill shares the same design as other basic bucket spinners – a bucket filled with grinding media and rotated on its own axis. But this design takes advantage of centrifugal force and the Coriolis effect to grind materials to a very fine or even micron size. These forces come into play as the grinding container in a planetary ball mill rotates on its own axis in the opposite direction of the frame (referred to as the sun wheel) to which it is affixed. These opposing movements, along with the difference in rotating speeds, result in the powerful combination of friction and impact forces required for the fine level of grinding afforded by the mill.
A design such as this is often used in large commercial installations and can get quite sophisticated. Simply determining the optimum rotational speed (called the Critical Speed) is a significant physics challenge. Spinning too fast or too slow greatly affects the efficiency of the mill. The Wikipedia entry for "Ball Mill" has a great article on the whole process.
ATTENTION!!! THIS BUCKET SPINNER DESIGN IS ONLY INTENDED TO ASSIST IN UNDERSTANDING BASIC PRINCIPLES AND SHOULD NEVER NEVER EVER BE USED AS A LEGITIMATE PULVERIZING TOOL. WORKING WITH CENTRIFUGAL FORCE IS NOT ALWAYS INTUITIVE AND CAN BE REALLY REALLY DANGEROUS. PROPER OPERATION OF SUCH A TOOL CAN REQUIRE SPEEDS REACHING SEVERAL THOUSAND RPM. THE DESIGN SHOWN HERE HAS HOME BREW ENGINEERING, BEARINGS THAT ARE WAY TOO INADEQUATE, NO PROTECTIVE CAGE, ETC ETC FOR ANY KIND OF SPEED BEYOND A FEW RPM. SERIOUSLY., JUST DON'T DO IT.
This design follows the same methodology as the other spinners - mostly just connecting things together - ala a Construction Kit. The idea here is to provide a collection of pictures, in order, that will explain how assembly is accomplished. By viewing each picture, in order, and hovering the mouse over the image, an Image Note will pop up and explain what the intended action should be for that step.
Comments about the process:
All the major pieces are out of 1/2" cast iron pipe. Except for the legs, per the picture. There are only a couple of different sub-assemblies, that get duplicated and connected, as you'll see in the images. Lengths for each pipe are arbitrary - I made the 2 pieces for the top and bottom just barely long enough for the frame to clear the length of the canisters, but obviously that will depend on the length of the canisters. The only crucial thing is to make sure the same lengths are used for opposing pieces.
The chain connecting the axis to each canister axle is standard #35 chain, cut to length. Sprockets are from Amazon, as described in the picture notes. Typically the axle sprocket is larger than the canister sprocket, allowing the canister to spin at higher speed. It's important to note that the sprocket on the axle is stationary - IT DOES NOT SPIN. Rotation of the frame causes the chain to continually wrap around this sprocket, thus driving the canister in the opposite direction. This is a major feature of planetary mills.
I opted for canisters made of 1 foot sections of 4" schedule 40 PVC pipe, with pipe plug fittings on each end, all available at Lowes. This allows for very simple design, including the bolts on each end that fit into the 608 bearings. Although the 4" Schedule 40 pipe has 1/4" thick walls, with repeated use they are surely going to have a short life so i picked something that would be simple, cheap, and easy to replace - sort of like "disposable" canisters. The 3/8" factory bolts that go through the center of each end plug were replaced with longer 5/16" bolts, so they will fit nicely in the 608 bearings inside the copper inserts. See pictures.
Larger canisters are possible, both in diameter and length - just a matter of adjusting the frame pipe lengths. As you will see if you read the Wikipedia Ball Mill entry, the length of frame pipe that separates the main axle from the canister is significant. The radius of the canister (planet plane) circling the axle (sun plane) is an important variable when calculating centrifugal forces.
The entire spinner is designed to be scale-able, mostly by simply varying the pipe diameter and lengths.
Step 8: Results
The STEM class wasn't able to construct nearly as many spinners as the staff had hoped. Most devices actually completed were simple variants of the original inner and outer frame. Creativity mainly applied to various methods of mounting container buckets within the frames. At the conclusion of the project each student had to submit a report describing their favorite use for a Spinner and how they would design/construct it to best perform their chosen function.
Here's a list of some of the more interesting ideas:
1) A student's older brother uses a custom trail mix recipe when he and his friends go on long hikes. Blending everything together, in the quantities needed, is a big job. Could a bucket spinner help?
2) One of the students was intrigued by the ability to 3 dimensionally spin. It reminded her of a carnival ride she saw at the fair that was 3 concentric rings moving independently of each other, supposedly to emulate weightlessness. She was interested in space travel and wanted to see what would happen if a mouse cage were strapped into the middle of a very slow 3D spinning frame, over an extended period. Would the inhabitants adapt and survive?
3) The school science teacher mentioned that the gravitational pull on Mars was 40% less than Earth. If earthlings lived on Mars for a long time their muscles would atrophy and bones would permanently weaken. But what if gravity was stronger - would the opposite be true? If a mouse cage was twirled fast enough, would it "use centrifugal force to simulate increased gravity". Would a mouse inside survive ok, and maybe even develop bigger muscles and larger bones? a SuperMouse!
4) A student was new to rock polishing and wanted to build something that was not so much a production tool as a research gadget. As mentioned in a prior section, he had accidentally discovered that a simple alteration of mounting the bucket at an angle inside the frame rather than totally horizontal would not only tumble the contents but also toss things left and right. Seems like it would significantly increase agitation but how much difference would it really make over time? he created a design to mount two buckets - one completely horizontal and one at an angle, to see how results compared.
5) Another student was also interested in rock tumbling and wanted to take the comparison idea a step further. He was confused about so many different recipes for polishing media - literally dozens of options. He designed a cage that would be mounted inside the frame, sort of a 3 x 3 matrix to hold 9 one pint paint cans, each holding a different media, and wanted to run simultaneous tests to compare mixtures.
6) The craft closet had a huge selection of paint colors for projects, but many of the little jars of paint were getting old. Seems that the paint inside was still good but it was a super-pain to "un-coagulate" the contents any time a project needed a paint job. Put a few BBs in each jar then stuff a large bucket with padding after all the jars were inside - spin the bucket for a couple days, see if it would help.
7) One of the girls in class had an aunt who sold spices at the weekly Farmer's Market. She had 34 different varieties of secret spices to add to sour cream or mayonnaise to make homemade chip dip. Business was great and the student would sometimes be recruited to help with mixing all the individual recipes. Spice ingredients had to be mixed in a big plastic bucket before being put into little bags, 34 different times, and some of the spices wouldn't mix very easily. Bingo!
8) One of the fathers was big into hunting, even reloaded his own ammo. Before reloading, each of the used brass casings had to be cleaned. Would a bit of car polish tossed into a small spinning bucket containing empty shells and play sand make everything look like new?
9) A student who lived on a farm needed to mix some animal feed in large quantities. Using larger and longer pipe, could the frame be scaled up large enough to hold a 55 gal drum?
10) Another of the girl students, our very own 9th grade intellectual, was curious about the difference between "rotating" vs "spinning". She defined Spinning as a bucket placed in the center of a frame and Rotation as a bucket placed near the outside perimeter. She wanted to test various mixing methods, see if bucket placement made a difference.
11) The only student mentioned by name in this Instructable is George. George didn't come up with much of anything that would benefit from a spinning bucket, but we mention his name here anyway because he is convinced he will someday be famous and feels the need to become accustomed to seeing his name in print.
12) A grandmother of one of the students has a nice collection of old drawer handles that she would like to display if she could figure out how to clean them up. Most are shaped in intricate ways and will take lots of scrubbing. They appear to be mostly aluminum, brass, sometimes copper, and seriously tarnished. The student wants to use a spinning bucket as a tumbler (like a rock tumbler) and polish them to a glass-like finish, shiny as a polished stone.. He thinks aluminum rubbed to a mirror finish is especially beautiful. A well-respected machinist who has a very nice industrial tumbler told him that putting a chrome-like surface on aluminum is very difficult, takes a huge amount of buffing with finer and finer rouge, and can never be accomplished merely by tumbling. But the student noticed that the machinist always uses dry media, and only spins at high speed for a short time. He wants to try wet media like the rock guys use, spin for a much longer time. He can't get the machinist interested but wants to try it himself.
13) One of the staff instructors wanted to try to make a ball mill - basically a rock tumbler on steroids. It can be used for crushing most anything into a very fine power. It's sort of like an automated mortar and pestle. Steel balls are tumbled, under pressure, with whatever needs pulverizing. For instance, in the old days a mill stone was used to turn grain into flour. The mill stone was very large and heavy, thus the pressure from gravity. In a ball mill the container spins at high speed, replacing gravitational force with centrifugal force. But administration troubles ensued soon as the instructor explained that he wanted to sling around a bucket full of several pounds of something at 3000 rpm. The admins tried to delicately explain that, without some serious engineering, such ideas could result in things breaking and people dying. The staff lawyer, concerned about liability, also explained it, but not nearly so delicately. The metal frame discussed in a prior section was the result of the discussion, but only with strong assurance that the speed of the device would never exceed a few RPMs.
But the problems involved in dealing with pent up energy stored in a heavy object spinning at high speed really captivated another of the students who follows the annual Punkin' Chunkin' contest. Every year several thousand people gather at a farm in Delaware to watch a bunch of crazy farmers see who can do a maximum pumpkin toss. For years it was just a bunch of off season farmers having fun with medieval technology, but as the years progressed the machines got bigger, and better, and far more expensive. Winning entries are now way beyond catapults and trebuchets. There are air cannons, hydraulics, centrifugal monsters. Guinness says the current record for distance is well over a mile. Physics says a gourd tossed that far, using the energy applied only at the very beginning of the flight, will necessarily have to reach several hundred miles per hour. Every year technology advances, but every year new problems crop up. Big problem now is preventing the pumpkin from self destructing when it cruises through the sound barrier. Anyways, it's the centrifugal machinery entries that is relevant here. The fascination was with the idea of moving Alaska Bucket Spinning technology into the realm of centrifugal force. It's the ol' slingshot idea - the thing that David used to take out Goliath. So the student and his dad wanted to springboard the student report into creating a contest at the Alaska State Fair - a Maximum Tomato Toss. The student had several good ideas about how a bucket spinner could advance into a serious tossing machine, but far as I know he's still working on a trigger mechanism, and how to aim the thing. The guys in Delaware might have some useful ideas, but how much pumpkin knowledge can be transferred to tomatoes? Those familiar with the Alaska growing season will understand that the biggest challenge may be to first get a 2 lb late season tomato to make it to fruition before frost. Many questions remain. Is it easier to toss a pumpkin over a mile, or a tomato? "Well, it sorta depends..."
Step 9: Late Breaking News
After experimenting with what's required to build a ball mill, and enduring the threats of incrimination from administration about the irresponsibility of exposing an entire class of students to flying projectiles, I pretty much threw in the towel for designing a pulverizer/grinder. But that was before i discovered Garbage Disposals.
Basically, a garbage disposal is a planetary centrifugal ball mill. See the picture above of the interior of a disposal. The bottom plate is the Sun gear, and the 2 spinners (planets) whirl around the parameter. Centrifugal force and rotating planets press material out the sides, grinding them up in the process. A disposal spins VERY fast, is properly engineered, built like a tank, requires no maintenance, is enclosed inside a safety barrier, available used at recycle shops, and the nicer ones are amazingly quiet - quite a feature for most ball mills. Bingo! A Planetary Centrifugal Grinding Machine for everyman. Could be the topic of the next Instructable! And setup is incredibly straightforward. In the picture above you'll see that the discharge pipe is simply redirected into the inlet from the dishwasher. The 3rd video at the beginning of this Instructable shows it in action. Images at the top of the page show raw metal shavings, then these same shavings after 2 minutes of spin, and then after 12 minutes. Looks like there's some serious potential here. And soooooo simple! But nothing of value is without challenges, right? In this case the plumbing gets easily plugged on the way back into the intake. It's a great opportunity to enlarge the outlet into a separate container, perhaps allowing for multiple disposal feeds and facilitating a filter/exchange system so the cycle can be continuous, just like the big commercial units. Also there appears to be a method of keeping the motor at a moderate temperature so it can run for hours/days.
There seems to be significant interest online about the best way to grind aluminum into powder, which has a multitude of uses. But it's tricky. Pulverizing aluminum inside an enclosed space will cause the fresh metal surfaces to instantly react with atmospheric oxygen, producing explosive aluminum oxide. Keeping the new metal flakes immersed in water can be helpful for that but the oxidation process is so strong it will actually steal oxygen from the water, resulting in the release of quite a bit of pure hydrogen, also explosive. But these are problems faced by quite a few commercial aluminum vendors, and appear to have adequate safety solutions. If you've read all the way to the end of this rambling Instructable then you quite possibility have an interest in such matters. If so, stay tuned!
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