Bottlecap Bonsai




Introduction: Bottlecap Bonsai

Wrought construction iron rods from the last home improvement project and a selection of bottle caps from the simpler time I thought that they will become the currency in case of emergencies, instead of toilet paper. With those items in mind only one thing came to mind, throw magnets at it, even better throw bottle caps at magnets. I present to you the Bottle cap Bonsai.

Like a real bonsai you can groom it, style it but even I could not neglect it enough for it to just die, R.I.P. poor potted plants. In the course of this instructable I am going to take you through the process of bending and welding together a construction iron tree trump, different types of cleaning processes to rust iron or steel in order to create a well, rustic look and design processes for future improvements.

While this project does involve welding you don't have to be good at it, it is the perfect project to practice. If you manage to lay down a perfect weld, awesome, if it does not turn out as expected, yay structure, it's a tree trunk not a pipeline. So with that said lets get to sculpting your own Bottle cap Bonsai.


The stuff you'll need is listed below, I am going to structure it into the main steps of the project, additional I am going to give you options of optional or replacement tools that you might have in your shop.

Bonsai tree trunk:

  • Wrought iron rod:
    • construction iron rods that are typically embedded in concrete. You can go out and buy or use straight new pieces, I am going to use pieces that were pulled out from a concrete wall
  • Hacksaw

  • Bench wise:
    • As expected these rods require some amount of force to bend them, so a stable bench wise is a must. It is thereby not important to have a big expensive vise, the important thing is that the thing is solidly connected to something you cant move.
  • Welder:
    • There are no special requirements to the welder in this project, stick, MIG, MAG or WIG pick your poison.
  • Wire brush:
    • Depending on the state of your iron rod or welding type you might not need it, but the first step of a good enough weld is always cleanup.
  • Wire or Tape:
    • to temporarily connect your iron rods together before welding.

Tree trunk rusting process:

I am going to present to you 3 different methods of cleaning your metal, so the first three entries in the following list exclude each other.

  • Hydrochloric acid
    • breathing mask: a must have
    • gloves: a must have
    • acid safe container or brush
  • Angle grinder with wire brush
  • Sandblasting cabinet
  • Acetone
  • Spray bottle
    • (clean, I'd say trink water safe, the finer the spray the better)

Bonsai bud:

The end result of this instructable will have buds created via 3D printing, additional I will demonstrate another method of creating buds using Fusion360 and iron pipe, so the first two entries in this list will exclude each other.

  • 3D-Printer
    • Broncefill filament
  • Iron pipe

    • approximate 10mm inner diameter (+1mm possible)
  • Magnets:
    • 10mm diameter, 2mm height
  • Bottlecaps

Step 1: Gather Your Supplies

As you can see in the image, the iron rods I've got are dirty, slightly rusted but above all covered in cement, all of that does not mater for this project.

The welder I am using is a MIG/MAG machine using flux core wire without any gas.

The magnets themselves are readily available on Amazon, AliExpress or any other online store of choice.

Step 2: Get to Bending

As a first step cut down long unwieldy pieces into lengths that can accommodate the following:

  • A base bend consisting of a 4cm straight followed by a nearly 90 degree bend
  • A trunk section to the height you want
  • A branch bend
  • A branch the length you want it to be

Using already bent pieces like mine actually works in your favor, the goal of the first bends is to straighten out existing bends. During this process you will see that due to the material forming to the original bend they won't get perfectly straight again, instead they already start to look like tree branches.

The process and the result are shown in the first two images.

If your pieces are still to bent you can flatten the curves by putting it in the vise like shown in image 3 and clamping it.

Step 3: Create the Basis Bend

In order to fixate the tree to a base later the individual bent rods should come together to form a star shape when looking from the top. So every individual rod should have a bend at the bottom that is either 90 degrees for a straight rising trunk or individual angles if your trunk is leaning.

The process and the result are shown in the two images. As a good tip, try to bend towards the wall, even when you are using metal work benches you are able to move them pretty easily by pulling with your body weight from the wall.

This is also the next tip, use your body weight, you don't have to have the biggest bicep to bend these things. Use dynamic force by ramming into it, it will start to bend easy, careful not to impale yourself on the rod.

Step 4: Bend the Trunk and Branch

Now get creative, work out how far up the tree the branch should be and
bend it to shape like in the base bend. Since it is difficult to estimate the correct length prior to bending, just cut of excess material.
Always keep in mind that the trunk consists of multiple iron rods so the trunk section of the individual sections should match in their general form, big gaps will make the welding process more difficult.

To keep track of your progress you can already start to assembly the tree using wire or tape.

Step 5: Tag It Together

After you are happy with your tree, we can get on to welding. As you
might expect the rope or wire is not really temperature resistant so if you try to weld a whole section while still holding it together with tape it will melt and you'll see your tree crumbling through your welding helmet.

So connect neighbor rods in the trunk by connecting them with short and fast tag welds. In order for these beads to stick you should clean of the area you want them to be with a wire brush. For me with all the concrete attached to the rod this process is especially important.

Now create small beads in the cleaned spots that just connect the neighbors together, these have to be neither really structurally sound nor beautiful to look at as they are covered by later welds, they are there so you can remove the tape and everything stays together.

Step 6: Weld the Trunk

After connecting the rods with tag welds you can remove all the tape or wire and clean of the whole length of your desired welds. Please excuse that I won't present you with any clear instructions on how to weld, I am myself a novice and the result you see in the second picture is pretty much the first time I ever welded iron rods together.

If you want to learn to weld, there are excellent videos on YouTube. If you already know how to approximately set your welder, you should start by practicing. Weld together random pieces that are left, no good welder got what they are without burning through one or multiple pieces. Trust me learning this new skill will greatly improve your abilities for future projects as it will open up completely new possibilities for you.

Step 7: Cleanup: Setup

In this and the next steps of this instructable I will present different methods of cleaning metal.
Now at first I will have to be more specific, the goal of this process is to rust the iron rods, so cleaning means to remove everything from a piece that prevents it from rusting in the first place.
To demonstrate this I cut off 4 pieces from a new iron rod. Now as you can see evidently they already rust, but creating a rust layer covering the whole piece is still difficult due to something that happens during the production process.

Manufactures don't want their product to rust straight away so what
happens is that they apply a slightly more rust resistive surface coating, an oxide layer. Most of the time this will happen by itself if hot iron or steeled is cooled with an oil bath.

I will show 3 different processes of removing this coating or layer from the metal:

  • yellow, sandblasting
  • green, wire brushing
  • red, aka danger, hydrochloric acid
  • white is the comparison piece

Step 8: Cleanup: Sandblasting

Sandblasting the piece creates a very uniform and slightly roughed up surface to the piece.
A simple sandblasting cabinet can be a great addition to your shop. I am using mine not only for metal pieces but also to clean up and sand down 3D prints.

Including costs to buy a cabinet, a compressor and the sandblasting medium this is the most expensive method, but also the least time-consuming and safest one mentioned here.

Step 9: Cleanup: Wire Brushing

I would recommend using an angle grinder with a wire brush attachment for pieces large and small. Due to multiple cleanups of my shop the angle grinder wire brush vanished into oblivion and will only return once I don't need it anymore, so the cleanup in my case was done using a Dremel and its brush.

As it can be seen in the comparison the piece becomes very shiny as it the process will remove the coating and polish the underlying iron. Using a Dremel this was of course the most tedious and difficult method to remove the coating, although it is easier and faster using an angle grinder.

Step 10: Cleanup: Hydrochloric Acid

Using Hydrochloric acid will require you to wear protective equipment, gloves and a breathing mask are a must. For the gloves simple rubber gloves will do, using a cheap brand you should probably double glove as you are handling metal pieces that can easily pierce a glove.

The breathing mask should be rated for chemicals and not only dust.

The process itself is really simple otherwise, but the acid into a cup and just through the rod into it. After a few seconds you will hopefully only see and not smell why I strongly suggest protective equipment, the acid will turn green, bubbles will appear on the surface of the piece and a gray green vapor will start to rise. After a few minutes or after an hour depending on the coating and material you use. Immediately after removing the piece from the acid wash it down with water.

While the process is by far the easiest one to do as you simply wait most of the time it is by far the most dangerous, especially when handling larger pieces a cup might not be enough and you are forced to wipe or brush the acid onto the piece.
On the other hand this process leaves behind a very, very reactive surface on the treated piece. The comparison picture was taken 2 hours after removing it from the acid, the slightest water film after washing it down was already enough to create very light rust.

Step 11: Rusting

In order to create an even layer of rust on the object, additional to the coating, grease and other impurities from handling the pieces has to go. For this I am using acetone, drench a rag or a shop towel in it and gently wipe down all surfaces you want to rust. Careful not to touch any after doing this.

Lay your pieces onto a surface that can get wet and start spraying them with clean water using a spray bottle. There should not be any residue of soap or cleaner in the spray bottle. Respray them when they are completely dry. Don't trench them doe, a light coat is what you want.

If you live in a humid environment you can simply place the pieces outside, otherwise just keep spraying them occasionally until you are happy with the results.

Step 12: Rusting: Result

The comparison in the image shows the pieces after 2 days of spraying them.

  • white:
    • here you can see the effect of the production oxide layer, although some
      rust developed it is far less than the other pieces and very spotty

  • yellow:
    • since sandblasting leaves you with a very uniform and pale finish the
      developed rust is also very uniform and bright in comparison to the other pieces

  • green:
    • While better than the untreated piece you can see that a lot of oxide is left behind and the rust is very spotty, your results may vary though depending on how tedious you are when wire brushing it.
  • red:
    • Since the iron is very reactive after the acid treatment this piece was
      the first one to develop a layer of rust, additional the rust is more integrated in the material instead of a light coating giving it a more coarse structure. Since the piece was darker than the sandblasted one the rust itself appears darker too.

Step 13: Create Buds for Your Bonsai

I present you with a typical situation, you have a great idea on how to do a specific thing, you plan it through in your head and you are happy with it. You get to your shop dig through a heap of leftovers but cant find the pieces you need.
Well at least I had this problem in this project, I needed a method to attach the magnets to specific places in the branches. The plan was to use metal piping to create little holders for the magnets. Unfortunately all hardware stores are closed around me due to the current crisis, so no fast fixes for missing pipe.

Ok so I cant try fitting pipe to the iron rod, the first solution was 3D
printing, instead of iron pipe I designed magnet holders in Fusion360. So I have a possibility to present to you a finished project and the bronze in addition to the rust turned out to be a good color match to.

If you don't have a 3D printer I will nonetheless take you through the process I use to construct and plan fabrication processes prior to ordering stuff online.

Step 14: Fusion360 Planning: Find Your Material

Most hardware stores have websites where you can search their product portfolio for the stuff you need.

So go to your store of choice and start searching for what you need, in case of this project I needed a pipe that can fit my magnets inside and that I can weld to the iron rod.

The best choice was a steel pipe with 12mm outer diameter, a 1mm wall therefore 11mm inner diameter, large enough for the 10mm magnets while not being too large, perfect.

Step 15: Fusion360 Planning: Draw the Base Pieces

Now that you have measurements for all the parts you need, start drawing them in a new Fusion project. For basic planning like in this case I present to you a concept called simplification from my actual field of study, computer engineering.

The basic idea of abstraction is to just leave out all the annoying real stuff that won't really make a difference. Real magnets have rounded edges that you can't really measure right, but you don't have to a simple cylinder is all you need.

The pipe is already the simplest shape so no need to simplify it further.

You will have to draw the iron rod to fit it, now surprisingly the shape of the rod is rather difficult to draw, it's
not really cylindrical, nor elliptical its just as it happens to be, there are ridges on it that run in different directions depending on the side of the rod. Again use abstraction look at it what it really is when you want to attach something to it, a nearly cylindrical object that is at most 9mm thick in my case.

Step 16: Fusion360 Planning: Work the Pieces With the Tools You Got

Since I want a bit more strength from my magnets, I insert two magnets into the pipe.

The holder should fit around the iron rod, so drill a 9mm hole through the pipe.

Cut the pipe at the middle of the newly created hole.

Step 17: Fusion360 Planning: Check the Fit

Start by adding in your simplified iron rod.

Now in reality the holder is welded onto the iron rod, this can be approximately shown in Fusion360 using the fillet tool. I apply a 4mm fillet for the weld. A voilà you have now virtually fabricated a magnet holder from steel pipe. If you are happy with the look you can now order or buy the material you need.

Step 18: Bonsai: Clean and Rust

Pick the cleaning method that you like and add buds to the tree.
In my case I sandblasted the whole tree going from image 1 to image 2. After cleaning it with acetone and spraying it with water for 2 days the tree developed a nice rust layer that can be seen in image 3.

Step 19: Add Magnets to the Buds

Press the magnets in the buds you created, for my specific strength of magnet I am using two magnets per slot for maximum attraction force.

Step 20: Plant the Tree

Anything you want can be used as a pot for your Bonsai, in the spirit of DIY I decided to create a simple laser cut box without a top.
Glue it together with wood glue and attach your bonsai to the bottom. The safest way would be to screw the trunk base to the bottom, I went the route of hot glue.

If you want to add the rustic touch to your wooden pot try firing it with a burner, careful not to really burn the material.
Add soil and you are pretty much finished.

Step 21: Add Bottlecaps

Groom the tree to your liking, the first bottle caps can be actually thrown at the tree while later ones have to be carefully placed.

Step 22: Bonus: Drinking Game

Turns out there is a really specific amount of bottle caps a magnet can carry on its own. Adding additional magnets to an already saturated magnet will let it drop another bottle cap even if you lay it carefully on top of a branch.

Start the night with an empty tree and observe in awe the rate the leaves build up, every buddy of yours has to add his bottle cap to the tree, drop it or another is another round, cheers.

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    2 years ago

    This is a really neat idea, I like it. Nicely done!