Before we delve into the basics of tattoo machine coils, what they’re made of, and how they work to power a coil tattoo machine, it may be helpful to first understand exactly what coil tattoo machines are and how they function from a high level. Tattoo experts feel free to skip ahead, but if you’re new to the industry and want a thorough understanding of coil tattoo machines and what makes them different from rotary and pneumatic tattoo machines, let us enlighten you.
The 411 on Coil Tattoo Machines
Tattoo shops have traditionally been associated with a pleasant buzzing/humming sound that only coil tattoo machines make. That buzzing comes from the way that a coil tattoo machine utilizes electromagnetic current to create and break a circuit that subsequently moves tattoo needles up and down and in and out of the skin. The breaking and re-establishing of the circuit happens in a cyclical fashion. When the machine’s coils are charged, the electromagnetic current pulls the machine’s metal armature bar down towards the coils, which then pushes the attached tattoo needles into the skin. That downward motion breaks the circuit previously created by the front spring attached to the top of the armature bar touching a neighboring contact screw, which causes the electromagnetic field to collapse, the armature bar to spring back towards the contact screw, and the needles to retract back into the tattoo tube. Once the front spring reconnects with the contact screw, the cycle begins again and repeats at a rapid pace (the precise rate of which is set by the tattoo artist) as long as the machine is in use. You can learn more about how coil tattoo machines work compared to their quieter rotary machine and less popular pneumatic machine counterparts in our blog post, Choosing the Best Type & Brand of Tattoo Machine for You.
There are many variations of coil tattoo machines. Some have single coils, others double coils, and others yet even have triple coils. Although many combinations exist, double coil tattoo machines are considered to be the standard for most tattoo artists who prefer coil machines. The shapes and sizes in which these coils come are even more diverse than the number of coils that different tattoo machines can utilize. Most machines tend to have 8-10 wrap coils, but those numbers can vary, too. Despite all these differences in number of coils, core heights, coil shapes, and wrap counts, all coils share a common purpose: to conduct power from a tattoo power supply unit, which charges the coils and turns them into the electromagnet that powers every coil tattoo machine, as described above.
The Basic Composition of a Tattoo Machine Coil
Think of a spool of thread, with its cylindrical core and flared top and bottom. It’s a little like a double-flare plug in shape, actually, but usually with more pronounced top and bottom discs. A tattoo machine coil has these same basic geometrical components; they’re just typically made with two metal washers and a cylindrical core comprised of a highly-conductive material like steel or iron in between them. (Soft iron is the ideal conductor, but most forms of steel will work, too. 
However, stainless steel is not a good option, because it’s non-magnetic.) When you stack the conductive iron or steel core on one washer and top it with another washer, you have a magnetic “spool” for what will become a tattoo machine coil.
A coil’s bottom washer typically has two holes drilled into it to provide a path for magnet wire (i.e. fine-gauge copper wire with enamel insulation) to be threaded up through one hole and eventually exit out the other hole. In between, the magnet wire is wrapped around the coil’s metal core up to the top and then back down, and always in the same direction (no switching between clockwise and counter-clockwise wraps). The wire is spooled tightly as it’s wound around the core from bottom to top, then a second tightly-wrapped layer overlays the first one as the magnet wire winds its way back down the core. This process of coiling the wire up and down the core is repeated until the coil has the desired number of wraps, which may be anywhere from 6 to 12 in most cases. At the end of the final downward wrap, the magnet wire exits the bottom washer through the second (exit) hole. Sometimes electrical tape is used as a final layer around the magnet wire wraps to hold them securely in place.
Alternately, specialty coil covers like our snake skin design and clear coil covers can be used for a more polished look.
Despite the presence of a metal core and magnet wire, a coil is magnetically weak until it’s charged. The two pieces of magnet wire protruding from the bottom washer become the positive and negative poles that will turn the entire coil into an electromagnet when it’s properly connected to a power source. If you wanted to test a homemade coil, you could connect one protruding wire end to the positive post of a battery and the other piece of wire to the battery’s negative post. Before doing so, you’d need to strip the enamel coating from the ends of the two pieces of wire protruding from the bottom washer to ensure optimal connectivity with your power source. Once connected, an electromagnetic circuit is established and an electromagnetic field (EMF) results, charging the previously magnetically-weak coil. That electromagnetic field concentrates in the top surface of the core, or the top washer, to be more specific. When the power supply is disconnected from the coil, it returns to its previous state and the electromagnetic field collapses instantly.
How Coils Make Your Tattoo Machine Tick… & Buzz!
Now that you understand the structure of the coils in a coil tattoo machine, our initial explanation of how coil tattoo machines work may make more sense. There’s a lot more to it, though.
When you plug your clip cord into your coil tattoo machine, current enters the machine through the rear binding posts that attach to the rear coil. From there, the current travels around the magnetic wire wrapped around the back coil core, out its top washer, over to the front coil (assuming you’re using a 2-coil machine), and into the front binding post, which puts a contact screw in touch with the machine’s front spring and completes the circuit. Once a circuit has been established, the iron or steel coil cores turn into magnets that draw down the machine’s metal armature bar, which hovers above the coils when they aren’t charged, as shown in the Feldman tattoo machine image to the left. When the coils are charged, the downward movement of the armature bar causes three things to happen almost simultaneously: (1) As the armature bar moves down, it pulls the front spring down with it. (2) The downward motion of the armature bar sends the attached tattoo needles into the skin. (3) The front spring loses contact with the contact screw above it, subsequently breaking the circuit that caused these three things to happen in the first place.
When the circuit breaks, the coils immediately return to being non-magnetic. Once there’s no electromagnetic field drawing the armature bar down, the front spring wants to return to its natural state, so it draws the armature bar back up until the spring is once again touching the contact screw above it. The circuit is instantly re-established, the coils’ cores are re-magnetized, and the 3-step process described above happens all over again… and again and again, as long as the tattoo power supply unit connected to the machine is turned on and the machine is in use.
Why the Number of Wraps & Coil Height Matter
Now that you know the technicalities of how your coil tattoo machine works, it’ll be easier to understand why the number of magnet wire wraps and the height of your coil’s core matter.
The height of your machine’s coils contributes to the strength and speed at which your machine will run. Shorter coils eat up more current and produce higher resistance, but they allow coil machines’ needles to hit faster. They also hit more softly, though, because of the higher resistance. Taller coils, on the other hand, make tattoo needles move more slowly yet more powerfully.
The number of layers of magnetic wire your coils have around them impacts the strength and speed of your tattoo needles, too, regardless of the height of the coils. The more layers of wire that are wrapped around each coil, the stronger and slower your machine will run. A coil with fewer wire wraps will make your machine work faster, but with less power. It’s a bit of a catch-22, because more wire leads to a stronger magnet that makes your machine work faster, but with less force. You may have to play around with a few different combinations to find the perfect coil-height-to-wire-wrap ratio that allows you to tattoo as quickly and deeply as needed while traumatizing clients’ skin as little as possible.
Quality Coil Machines Are Reliable Machines
Yes, we sell coil tattoo machines, but that’s not why we’re sharing what we’re about to tell you. Have you ever had a coil tattoo machine suddenly lose power only to start working a few days later, or had your armature bar stick to the coils or the contact screw and stay stuck? The problem may have resolved itself randomly, or your machine may have had an attitude adjustment after a few quick slams against a table top or other hard surface… or it may have just stopped working altogether. Why does this happen? It’s typically due to poor hysteresis, which is a delay between the electromagnetic field breaking and the coils’ magnetic state dissipating mid cycle, when the machine is turned off, or not dissipating at all. Usually this issue is due to poor material in a coil’s core that prevents its domains from returning to a random state when the electromagnetic field is broken. A build up of residual magnetism–which is typically an issue with cheaply-made coil tattoo machines–prevents the domains of the coils’ metal cores from returning to their natural, uncharged states. Sometimes giving your machine a good smack can realign the domains and demagnetize the cores. Degaussing is a less traumatic, but also much more expensive, alternative option for fixing this issue that involves demagnetizing by use of electric coils. Overall, the best option yet is to start out with a quality coil tattoo machine and avoid the issue of residual magnetism altogether!
References
Tattoo Machine Coils Tutorial by Brandyn Feldman of Feldman Electric
(Feldman Tattoo Machines Available for Sale on PainfulPleasures.com)
Coil Circuitry Information From AllAboutCircuits.com
Definition of Hysteresis From Merriam-Webster.com
Painful Pleasures Blog Post, Choosing the Best Type & Brand of Tattoo Machine for You
Painful Pleasures Article, Coil vs. Rotary Tattoo Machines
