shearing-machine-cutting-defects-bow-twist-camber

Introduction

There is nothing more frustrating than shearing a perfect strip of metal, only to have it curl up like a corkscrew.
In the shearing industry, we call these defects Twist, Bow, and Camber. While many operators blame the machine, the issue is often related to physics, setup, or worn-out shear blades.

Here are the 5 most common causes and how to fix them.

1. Cutting Strips That Are Too Narrow

The most common cause of twisting is simple physics. If you are cutting a strip that is narrower than 8x the material thickness, the metal will almost always twist.

The Fix: There is no machine fix for this. You must plan your nesting to cut wider strips.

2. Incorrect Rake Angle

The rake angle is the slope of the upper blade. A higher rake angle requires less force but causes more twisting.

The Fix: If your machine has an adjustable rake angle, reduce it to the lowest setting possible for that thickness. This flattens the cut.

3. Blade Gap Clearance is Too Wide

If the gap between the upper and lower blade is too wide, the metal will “fold” over the bottom blade before it cuts. This creates a nasty burr and causes the part to bow.

The Fix: You must adjust the gap based on the material thickness. Read our technical guide on [How to Adjust Shear Blade Gap Clearance] .

4. Dull or Chipped Blades

A sharp blade cuts; a dull blade tears.
If your blades are dull, they force the metal down instead of shearing through it. This vertical pressure causes the strip to bow downwards.

The Fix: Check your blades for shiny rounded edges. If they are dull, you can try rotating them to a fresh edge. If all 4 edges are worn, you must install new [High-Precision Shear Blades] to restore a straight cut.

5. Material Stress (Grain Direction)

Sometimes the machine is fine, but the metal sheet has internal stress from the rolling mill.
The Fix: Try cutting the sheet in a different direction (rotate the sheet 90 degrees) to cut against the grain.

Summary

If you have reduced the rake angle and checked the gap, but your parts are still twisting, your blades are likely the culprit.
At JSTMT, we manufacture [6CrW2Si and H13 Shear Blades] designed to hold a sharp edge longer, reducing the friction that causes twisting.

shearing-machine-cutting-defects-bow-twist-camber