How to Build a Jacob's Ladder With Knives





Introduction: How to Build a Jacob's Ladder With Knives


I am not responsible for any destruction of property, injury, death or inter dimensional portals that may result from following these instructions. If you are not familiar with working with high voltage, read about high voltage safety here and here before attempting this Instructable! Make sure that you NEVER have the device connected to the mains when you are working on any part of it. Make sure that you NEVER touch the device with any part of your body or conductive object while it is switched on. Attempt at your own risk.

This Instructable will show you how to create a Jacob's Ladder. I originally constructed this device to be part of The Electric Knife Orchestra that you can see in the video above. Jacob's Ladders are incredibly simple from an electronics point of view, a high voltage transformer connected to two electrodes, in our case, knives. The magic happens because the voltage is high enough to ionize the air in between the electrodes creating your own personal lightning bolt.

Step 1: Gather Materials

First of all you need to gather your materials:

  • 2 Knives: The knives that I used were 8" cook knives from a dollar store. Make sure the knives that you purchase have a smooth edge (i.e. are not serrated). This will allow the arc to travel all the way up the knives. The knives should also have a plastic handle held on by rivets (so that the plastic part can be removed).
  • High Voltage Power Supply: I recommend using a neon sign transformer as it will limit the current once the arc has started rather than burning out. You can find second hand ones on ebay fairly cheaply. Ideally, you want to find one that has an output voltage greater than 10,000V. The transformer I used was a Franceformer 12060 P5G-2.
  • 2 Through Hole Ceramic Insulators: These are to insulate the knives from the acrylic that is holding them up. I found mine at Apex Electronics but there seem to be some very similar ones available here as part number (ICR) 32103.
  • Wood for Base: I used a piece of film faced plywood. This should be the same size as, or slightly larger than, the acyrlic base which is 17.28" x 7.44".
  • Power Cord:This should be rated for a higher current than the transformer that you buy. Home Depot sells power tool replacement cords that would be suitable.
  • 2 Lengths of High Voltage Insulated Cable: These are for connecting your high voltage supply to the knives. The length will depend on where the high voltage terminals are situated on your transformer.
  • 4 32" x 18" Sheets of 3/16" Transparent Acrylic
  • 32 M3 x 12mm Pan Head Machine Screws
  • 2 M3 x 20mm Pan Head Machine Screws
  • 34 M3 Nuts
  • 2 #6-32 2.5" Pan Head Machine Screws
  • 4 #6-32 Nuts
  • 10 #6-32 Washers

Step 2: Remove Handles From Knives

The first step is to remove the plastic handles from the knives. The beauty of buying knives from a dollar store is that they are poorly constructed so the rivets should pop out easily. There's no definitive way of going about this but after a little experimentation I found the following to be fairly quick and easy.


  • Knives


  • Insert knife into vice with blade pointing down.
  • Try to separate the plastic from one side of the handle by hammering a chisel between the plastic and the metal, this should be enough to pop the rivets.
  • If there are rivets still remaining after using the chisel, you can use the claw of a hammer to pull them out.
  • Go through the same process on the other side of the knife.
  • Rinse and repeat for second knife.

Step 3: Laser Cut Acrylic

The next task is to laser cut the parts for the device. The Illustrator files are attached to this step. The parts are split up into four 32" x 18" files as that's the size of the bed of the laser cutter that I used. If you have a larger machine, you may want to consolidate some the parts into fewer sheets. There are two files that you may need to alter to fit parts that you find:

  • The mount for the knives is at the bottom of this file. It contains two capsule shaped holes that are sized to fit the ceramic insulators. The insulators I used were circular and had a 3/4" diameter at the section that goes through the mount. You will need to resize those holes if your insulators are of a different size. The holes are capsule shaped to allow the knife positions to be changed easily.
  • The bottom shape in this file has a hole that is sized to fit the base of the transformer, (in my case a Franceformer 12060 PG5-2). If the bottom of your transformer is of a different size, you should resize this hole accordingly.

Once, you've made any necessary changes, load the files into your laser cutting software. Most laser cutting software can accept Illustrator files but if yours doesn't, you can export the files from Illustrator as vector format that it does recognise.

Step 4: Construct Base and Sides


  • Wooden base
  • Base of case (laser cut acrylic)
  • Side of case (laser cut acrylic)
  • Knife mount (laser cut acrylic)
  • 2 M3 x 12mm pan head machine screws
  • 2 M3 nuts


  • Put the acrylic base on top of the wooden base.
  • Place the transformer into the hole in the centre of the acrylic base.
  • Insert the tabs in the knife mount into the holes on one of the side pieces and secure using a screw and nut. The nut will sit in the T shaped slot in the knife mount in the cross of the T. The easiest way to secure these kind of joints is to hold the nut in place while you screw the screw into it.
  • Insert the knife mount into the other side piece (ensuring both side pieces have the same orientation) and secure with screw and nut.
  • Slot the sides into the base as shown in the picture. We will put the screws in to secure the base to the sides in a later step.

Step 5: Attach the Knives

We're now going to attach the knives to the knife mount. The backs of the knives are facing each other so that the distance between the knives increases gradually as the electric arc climbs up them (even though the other direction might look a little cooler).


  • Assembly from previous step
  • Knives
  • 2 lengths of high voltage insulated cable
  • 2 #6-32 2.5" Pan Head Machine Screws
  • 4 #6-32 Nuts
  • 10 #6-32 Washers


  • Before starting to put everything together, check that the two lengths of cable that you have are long enough to reach from the high voltage terminals of the power supply to the knife mount holes but not so long that there will be lots spare.
  • The cables that I'm have terminals on them. If yours do not, you will need to strip their ends.
  • Attach a knife to the knife mount and cable using the ceramic insulators, screws, nuts and washers as shown in the first picture.
  • Tighten with a screwdriver and a wrench until the knife stands up on its own.
  • Repeat the last two steps with the other knife.

Step 6: Wire Up the Transformer


  • Assembly from previous step
  • Back of case (laser cut acrylic)
  • Power cord


  • Attach the cables to the high voltage terminals of the transformer. The high voltage terminals can be identified by the fact that they have a much larger insulator below them than the other terminals on the power supply. If you are unsure which terminal is which, read the documentation for your transformer.
  • Thread the power cord through the hole in the back of the case as shown in the second picture.
  • Wire up the power cord to the 110V terminals of the transformer. The cord I have has US color coding, so black is hot, white is neutral and green is ground. If you are unsure, read the documentation for your transformer to determine which wires should be connected where. In the case of my transformer, the hot and neutral wires are connected to the terminals with insulators underneath them and the green terminal goes to the terminal that comes straight out of the case.

Step 7: Adjust the Knives


In this step, we will adjust the position and angle of the knives to get an electric arc that consistently travels from the bottom to the top of the knives. N.B. The third photo is a long exposure shot so your electric arc will not look like this.


  • Assembly from previous step


  • Make sure you are nowhere near the device, plug it in and observe. If there is no spark, the knives need to be moved closer together. If there is a spark, but it doesn't travel up the length of the knives then the angle between the knives is too large.
  • ENSURE THAT THE DEVICE IS POWERED DOWN BEFORE ATTEMPTING ANY ADJUSTMENTS BY UNPLUGGING IT AND PLACING THE PLUG BESIDE THE DEVICE WHERE YOU CAN SEE IT. The knives can also become hot during operation so take care not to burn yourself. This is less of a problem than with a traditional Jacob's Ladder that has thinner electrodes, as there is more metal to absorb the heat.
  • Once you are sure that the device is powered down, you can begin adjustments.
    • Angle adjustment: unless your nuts are screwed on incredibly tightly, it should be possible to change the angle of the knives without loosening them.
    • Distance adjustment: to chance the distance between the knives, you will need to loosen the nuts at the back of one of the ceramic insulators. You should then be able to slide it towards the other insulator. Be careful of cutting yourself when doing this as, once the nut is loosened, the knife will fall down. Once you have a distance you're happy with, tighten the nuts back up again.
  • Go back to the first step and repeat until you are happy with the arc's behaviour.

Step 8: Add Front, Back and Top of Case


  • Assembly from previous step
  • Front of case (laser cut acrylic)
  • Top of case (laser cut acrylic)
  • 32 M3 x 12mm pan head machine screws
  • 32 M3 nuts


  • Pull the power cord through the back panel of the case until there is no slack left within the case.
  • Slide the tabs at the bottom of the back into the holes on the base as in the first photo.
  • Push the back onto the case so that the tabs on the sides go into the holes on the back.
  • Insert a screw on each side of the back to secure it.
  • Attach the front of the case in the same way as the back.
  • Put the top onto the case so that the tabs on the front, back and sides go into the holes in the top.
  • Now go around the case and secure everything with screws and nuts. To insert the screws at the bottom you will need to slide the acrylic case over the edge of the wooden base just enough to allow the screws to be inserted upwards.

Step 9: Admire Your Handiwork

Congratulations you've reached the end. The operation of the Jacob's Ladder produces ozone so be sure to operate this device in a well ventilated area. Don't run your Jacob's Ladder for too long in one burst as it may overheat, up to 5 minutes is probably OK. You may also have to adjust the position of the knives if the environmental conditions, such as humidity, change.

Some fun things you can do with your device:

  • Taking long exposure photos (see photo). You will need to experiment with ISO, aperture, timing and white balance settings.
  • Rubbing salt solution onto the electrodes and letting it dry will change the color of the arc.
  • Putting a relay in the power cord will allow you to switch the Jacob's Ladder on and off from a microcontroller. For The Electric Knife Orchestra, I used this solid state relay from Sparkfun rather than a mechanical relay as it can handle being switched on and off rapidly without burning out.

Once again, high voltage can easily kill you, treat it with the utmost respect at all times. Make sure that you NEVER have the device connected to the mains when you are working on any part of it. You can do this by making sure that it is unplugged and the plug is clearly visible on the table before doing any adjustments. Make sure that you NEVER touch the device with any part of your body or conductive object while it is switched on. Read about high voltage safety here and here before attempting this Instructable!!

Thanks for reading! If you like this Instructable, please vote for it by clicking on the vote ribbon in the top right of the page.

2 People Made This Project!


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We have a be nice policy.
Please be positive and constructive.




this is fantastic! Love the musical Jacob's Ladder.

Very impressive! I can't wait to see what you make next. The video is amazing!

2 replies

Thanks! Have a few projects on the go ;)

Great job, I think a fish tank would work great, at least a Jacobs ladder will live longer than what the fish do.

I posted a comment when I saw this the first time and it seems like it never actually showed up.

Anyway, just wanted to say that this is amazing! especially the video! And man... You sure are lucky to have so much parts and such a huge storage! :D

Well done project, with a clever twist using knives for the electrodes, and good writeup. To me, that adds up to a good Instructable!

When using a solid state relay to switch AC to a magnetic transformer like this, there can be issues with inductive kickback from the transformer when it's being switched off at random times during the AC cycle, which will produce voltage and current surges across the SSR. It's good pratice to overspec the SSR, and/or add some transient voltage protection for a load like this since it differs from the resistive loads most SSRs (zero crossing) are designed for.


It's no JOKE being dyslexic and you don't need to send me proof that I misspelled clever ? cleaver ? How ever it is spelled....

I was only trying to be nice so why can't peapel just accept when someone is just being nice....


Why are you making a big deal of me misspelling a word ?
I already told you I'm dyslexic so what's the problem

You misspelled Cleaver.

Dude your the one that misspelled that word!

He's the one that wrote it correctly!

Here's a link to the word for proof!

Joke....Explosivelegoman. Explosivelegoman...joke.

Now that we are all introduced. Its a video about hatchets, knives, and CLEAVERS banging away to play a song. Yes yes the original comment said it was a very CLEVER video, my comment was they misspelled CLEAVER.

Your ability to read along and have fun with a comment is greatly appreciated.


I'm dyslexic so it's a wonder I only misspelled one word thanks for letting me know

It's a perspex box, not the most penetrative of objects.

jacobs ladder? Always wonder what that thing was, what do they do? All I know is that every mad scientist has a few working in their labs.

1 reply

Absolutely nothing, they just look cool. They became famous for being featured in every boffin's laboratory, as you spotted :)