Tattoo machines come in two basic styles: rotary and coil. While coil machines have become the standard in many tattoo shops, there are quite a few tattoo artists who prefer the rotary machines that have been in use for some time now. For many artists it is a matter of style preference. They find that one type of machine suits their artwork better, and so have come to use that type of machine.
A coil machine is the type in widespread use today. It operates by using two coils of wire around iron rods to create a magnetic current when electricity passes through the iron rods. In design, it is almost exactly like the doorbell circuit on a home or apartment. Because the electricity passes continually through the coils (at least, while the artist has the switch pressed), it can generate a fair amount of noise, which may be off-putting to some first-time tattoo customers. For the artist, the two iron rods and coils make a reasonably heavy machine. Arms and hands may become very tired by the end of a long day of tattooing. This design means the machines are realtivley less expensive to buy, however, most artists will need to purchase two: one for drawing lines and one for shading. A coil machine cannot do both.
A rotary machine, however, can produce clean, crisp lines as well as beautiful shading. A rotary machine operates on a direct mechanism where electricity drives the needles up and down extremely fast. The ink is carried the proper distance beneath the skin. Rotary machines are much lighter since they do not require the two iron rods and surrounding coils. They are also smaller, which some female tattoo artists prefer, as they fit in the hand better. A rotary machine can draw crisp lines as well as create a large amount of fill color; coil machines can do one or the other, but not both.
A tattoo artist will require a minimum of two coil machines or two rotary machines; both, however, will require a large number of sterilized needles of various gauges.