What makes a liner tattoo machine a liner and a what makes a shader tattoo machine a shader?

The difference between the two machines is the gap of tension in regards to the armature bar to the frame as well the gap between the contact screw to the spring. For a liner, you will want there to be more tension with the bar and a little bit of give with the spring. For a shader, you will want there to be less tension with the bar and more with the spring. The age old reference tool for this in regards to the proper amount of gap between the screw and the spring is; the width of a nickel for a liner, and the width of a dime for a shader. With this said, this is not a universal reference and all machines have the potential to be different. It all comes down to the type of metal that your frame is made of, the type of metal your armature bar is made of, the quality of your coil wrappings, the electrical integrity of your power supply, etc., etc. You get what you pay for with tattoo equipment, and nowhere is this more relevant than with your machines, ink, needles and your power supply so don't be cheap when it comes to buying supplies.