Straightener

Straighteners
Straighteners come in two main flavors–pull-through (unpowered) and powered.

Pull-Through-Straightener
Pull-through straighteners rely on a feeder to pull the metal through the rollers. While these machines typically cost less and save space, inertia (resistance to any change in velocity, whether from rest to motion or vice versa), can result in less accuracy, less effectiveness and even marked materials if the rolls slip during starts and stops. While the feeder is usually separate from the straightener, there are all-in-one straightener-feeder machines. The same issues apply to these combo models, though.

Powered straighteners , while bigger and more expensive, do not have the same issues and therefore produce better parts. Instead of relying on the feeder to pull the metal sheet, a powered straightener has rollers that are driven to move the metal through. On some, the bottom roll is driven, while the top row is free. Others use a combination of both.
Speaking of the rollers, on a standard straightener, the rollers tend to be larger, because there's only one row of them, to prevent deflection, i.e., rollers bending. Standard powered straighteners are suitable for removing coil set from most metals and thicknesses.
There are also straighteners specifically designed for wires , with either two planes for round wire or a single plane for flat wire.

Precision-Straightener
Rather than large rollers, corrective levelers,employ a large number of smaller rolls that are backed with more rolls. This creates a very rigid, tightly spaced roller structure that can gradually work out tighter strip bends, as well as provide deeper stress relief for greater flatness and reduced metal-weakening stresses.
These are the only kind of straighteners that can fix camber, center buckle and edge wave, because they can change the shape of the metal from edge to edge and be adjusted to stretch just the sides or just the middle.

Calibration
As previously mentioned, you need to go 20–30% beyond the metal's yield point to ensure the metal will stay flat even after it goes through the press.
Unfortunately, there's no one-size-fits-all solution for metal straightening. That's because there are a wide variety of factors that need to be considered, including type of metal, material thickness, coil set amount and roller diameter and spacing. The required settings can even change for the same coil, due to increased coil set closer to the center, where the metal is more tightly wound.

SELECTED FOR YOU: The Differences Between Sheet & Coil Processing
That being said, a good place to start is by lowering the entry roll to the thickness of the material BELOW 0, and raising the exit to the thickness of the material. So, for example, if your material is .125” thick, you'd put the entry roller at -.125 and the exit roller at .125.
Straighteners and corrective levelers come with either computer or manual adjustments–both with readouts to make it a very simple task to adjust the height of the rollers to meet your needs.
When adjusting the roller heights, regardless the type of straightener, aluminum is much harder to straighten than steel due to it being more elastic. You need to come down harder on aluminum coils to get them straight.

Picking the Right Straightener
So, now that you know the basics, the question is–which machine fits your needs best, and what size do you need?

Before you call up a manufacturer, do some research into your needs and have the following information ready:
Type, thickness & width of material(s)
Voltage
Speed needed, i.e., how much material you'll be running in a certain amount of time
This information will help the manufacturer design, develop and build the machine that meets your needs.