Process
Wire straightening
Coil is not a straight stick. Cast and helix left in the wire become bow, twist, and missed hole patterns after the first bend. Straightening is the first station on a real 4–14 mm cell.
What wire straightening is
Wire arrives as a coil. That coil has a natural curvature (cast) and a corkscrew (helix). A straightener takes those out — or most of them — so the feed length that reaches the bend head is a known, repeatable centerline.
On light spring wire, a cheap two-plane roll stack can be enough. In the 4–14 mm band, coil energy is high. A weak straightener does not fail loudly. It prints a banana into every long span and a twist into every 3D form.
Why it comes before the first bend
Bend programs assume the incoming wire is straight. Compensation for springback lives in the angle. Compensation for a crooked feed lives nowhere — it shows up as a first-article that will not sit in the fixture.
- Long legs and frames magnify leftover cast.
- 3D rotation turns leftover helix into out-of-plane error.
- Pre-coated wire (galvanized, painted) marks if the straightener is too tight or too dirty.
Rotary vs roll
Roll (two-plane) — stacked rollers in vertical and horizontal planes. Common, adjustable, good when the alloy is mild and the diameter is mid-band. Setup is a craft: too little pressure leaves cast; too much work-hardens the surface and marks stainless.
Rotary — the wire passes through rotating dies or rollers that wipe cast more uniformly around the circumference. Used when residual bow has to be low on long spans, or when the coil is ugly. Rotary units are larger, and they have to match the diameter — a 14 mm rotary is not a 4 mm rotary with the pressure turned up.
Some cells combine a rotary take-out with a finish roll stack. The print never sees this. The fixture does.
What changes from 4 to 14 mm
| Diameter | Inch | Straightener reality |
|---|---|---|
| 4 mm | 0.157 in | Two-plane roll is usually enough. Watch coating mark on pre-galv. |
| 8 mm | 0.315 in | Cast energy is real. Roll stack must be sized for the tensile, not just the diameter. |
| 12 mm | 0.472 in | Long frame spans need a serious straightener. Leftover bow is a fixture fail. |
| 14 mm | 0.551 in | Rotary or heavy roll. Light spring straighteners do not belong on this coil. |
What to spec (and what not to)
You do not call out “rotary straightener” on a part print. You call out straightness where it matters: bow per length on a long leg, twist relative to a datum, and the hole or weld pattern the form has to hit.
If the wire is pre-coated, say so. Straightener pressure that is right for bare 1018 will skate or crack a zinc layer. If the coil is high-tensile, say the spec — straightening a spring-temper rod as if it were mild steel is how you get a part that looks straight on the bench and walks after the first bend.
Related
- Cut-to-length — cutoff after a straight feed
- 3D CNC wire forming
- Design for wire forming