Make Your Own Curie Pendulum (Heat Engine)

Hello fellow makers,

Today I would like to show you how I made this Curie pendulum. This is a simple curie effect heat engine and is a great way to demonstrate this important scientific principle.

The curie effect usually refers to a magnetic phenomenon discovered by Pierre Curie. He discovered that ferromagnetic substances exhibited a critical temperature transition, above which the substances lost their ferromagnetic behavior. This is now known as the curie point.

When our pendulum that is heated by a candle reaches its curie point it is no longer attracted by the magnet and swings out of the flame, now out of the flame the pendulum cools down and is attracted by the magnet again.

Let's get started on making your own...

To make this Instructable you will need the following:

• About 300mm of 4mm brass brazing rod

Amazon - Bronze Rods

• A strong neodymium magnet

Amazon - 10mm x 20mm Magnet

• A nickel coin

Wikipedia - Coins of USA

• Wooden tea candle holder

Amazon - Wooden candle holder

• Tea candle
• Dremel/multitool with abrasive cutting disks and felt pads
• Butane torch
• Silver solder

Amazon - Silver solder

• 0.8mm drill bit
• 4mm drill bit
• Sewing needle
• Leather safety gloves

Amazon.com links included for reference.

First we are going to need to make a hanger for the pendulum.

To make this I used the same 4mm brass rod as we will use for the pendulum.

Start by cutting off a 200mm piece of brass rod.

We are going to have to anneal the section of brass rod that we want to bend otherwise it will be extremely difficult and you could cause it to fracture.

Put on some leather safety gloves!

To anneal the brass rod we will need to heat the section with the butane torch until it is a nice cherry red color and then quench it in water, this will soften up the brass and allow us to bend it easily.

* If you have experience with handling hot metals you can also bend it without quenching it first, this will give you much better control over the bends. Just take care as touching red hot metal WILL cause serious burns.

I decided to go with the hook shape as pictured to make fine adjustments to the position of the pendulum over the flame easier, but you can really go with any shape as long as it suspends the pendulum.

Next we are going to take the Dremel with an abrasive cutting disk and make a slit of about 1mm wide and 5mm long through the end of the hanger, this will be where the pendulum is suspended.

Now with the 0.8mm drill bit make a hole through the slit about 2mm from the end, this is where the needle will go through to hold the pendulum in place.

For the pendulum you are going to start by cutting off about 100mm of the 4mm brass rod. The length will depend on how you make the pendulum hanger and your candle holder (how far away your flame is from the pendulum), when the candle is lit we want the flame touching the nickel coin.

Using your abrasive cutting disk flatten about 5mm of one of the ends of the rod to a little less than 1mm so that it fits into the slit made in the hanger, you want it loose without any friction.

Now with the same 0.8mm drill bit drill a hole in the centre of the flattened part as pictured.

On to the coin, this is an essential part.

We are going to need a nickel coin, the easiest method to find one is to search for your local currency on Wikipedia and look for a coin that is fully nickel.

* Take note that a lot of modern coins are nickel coated metal and this will not work well.

Curie temperatures of metals:

Metal: Degrees: C / F

Iron (Fe) 770 / 1418

Cobalt (Co) 1130 / 2060

Nickel (Ni) 354 / 669

Gadolinium (Gd) 19 / 66

Dysprosium (Dy) −185.2 / −301.3

Neodymium magnets 310–400 / 590–752

Alnico 700–860 / 1292–1580

Samarium–cobalt magnets 720–800 / 1328–1472

Strontium ferrite 450 / 842

As we can see in this table nickel gives us the lowest curie point for commonly available ferrous metals.

To attach the nickel coin to the pendulum we need to use some silver solder, note that you cannot use regular lead/tin solder as it would melt in the heat of the flame.

I placed the brass rod against the corner of the nickel coin on my old metal drill press table and heated the joint up to a bright red, once it was up to temperature I pressed the silver solder rod (fluxed) against the joint and allowed a nice pool to form around it creating a permanent joint.

Clean off any flux left over from the solder.

This is not necessary for proper operation of the heat engine but before assembling the parts I decided to polish all the brass parts using a felt pad and some compounding polish as annealing the metal leaves behind heat marks.

Next I placed the flat end of the pendulum into the slit of hanger and pressed a sewing needle through the holes drilled earlier.

Snip off the excess of the needle with some pliers, the flat spots made by the pliers when snipping off the excess should be enough to keep it from sliding out.

Now we need to drill a 4mm hole into the wooden candle holder for the pendulum hanger to stand in.

To find the correct spacing place a tea candle into the holder and light it, now position your hanger onto the holder so that when hanging freely the nickel coin is just out of reach of the flame (less than 1mm from the side of the flame) then mark the position.

Now drill the hole with the 4mm drill bit.

Slide the hanger into the hole and use some epoxy/CA glue to hold it in place if it's not a tight fit.

To make the curie pendulum function we are going to need a strong neodymium magnet, the one I used is a 10mm by 15mm magnet from an old shake flashlight.

First we need to atatch the magnet to the candle holder next to the hanger.

The polarity of the magnet is not important, one of the poles just needs to be facing upwards.

I used 2 part CA glue to stick it down as pictured, you can also hide the recess the magnet inside the holder by drilling a hole the same size as the magnet and gluing it inside of the hole.

The magnetic field of the neodymium will be redirected to the nickel coin with the help of a ferrous material. I used a long 6mm bolt that I heated up with the butane torch and made a 90 degree bend at the correct height and then just cut off the excess.

The length and shape of your bolt will depend on your hanger setup. The tip of the bolt needs to be just out of the flame but we need the magnetic field at the tip of the bolt to attract the free hanging pendulum so that the coin is held in place over the flame of the candle.

- Magnet is not releasing the pendulum:

• When you first light the candle it might take a few minutes for the coin to heat up to working temperature.
• If after 10 minutes it still isn't working try moving the flame up closer to the coin.
• Make sure your coin is 100% solid nickel, sometimes even different years of the same coin has different compositions.

- Pendulum released but did not get attracted again:

• If the coin is still being touched/heated by the flame after reaching its curie point it won't be attracted again until the flame is removed/moved a little further away.

- My curie pendulum worked for a few minutes then stopped:

• As with any heat engine if it is not cooled enough it will eventually overheat and stop working until it has cooled down again. Try lowering the flame a little of move the pendulum to a location where there is a slight breeze, this will help the pendulum cool when it is out of the flame.

Light the candle, sit back and enjoy.

With small adjustments to the flame position you will find a sweet spot where the pendulum will swing back and forth endlessly.

Hope you guys enjoyed this Instructable and get tons of enjoyment and hopefully not too much frustration out of it.

If you have any questions or suggestions please leave a comment below and feel free to share your own creation with me and the Instructable community by clicking the "I Made It!" button below.

Thank you for reading and HAPPY MAKING!