A shearing machine looks like the simplest machine in a fabrication shop and is often bought as an afterthought — usually right after a press brake. That ordering is backwards. The shear decides the quality of every blank that reaches the brake, and an inconsistent sheared edge shows up later as bend-line variation that no amount of ram accuracy can correct.
This guide covers the specification decisions that matter, in the order they should be made.
Step 1 — State cutting capacity correctly
Cutting capacity is always a pair of numbers: maximum thickness and maximum length, at a stated material. A machine rated 6 mm × 3200 mm is not a machine that cuts 8 mm, and it is not necessarily a machine that cuts 6 mm stainless.
Material strength scales the requirement. Use these factors against the mild-steel rating:
| Material | Typical tensile strength | Capacity factor vs mild steel |
|---|---|---|
| Mild steel | 400–450 MPa | 1.00 |
| Cold-rolled / galvanised | 450–500 MPa | 1.05–1.15 |
| Stainless steel (304) | 600–700 MPa | 1.40–1.60 |
| Aluminium (5052) | 230–250 MPa | 0.55–0.65 |
| High-tensile / wear plate | 700–900 MPa | 1.60–2.00 |
If stainless is more than an occasional job, size the machine for stainless and let mild steel run comfortably under capacity. The reverse approach — sizing for mild steel and pushing stainless through — is the single most common cause of premature blade failure and cracked cutting edges.
Thickness is not the only limit
Two further limits are often overlooked. Minimum thickness matters because thin sheet can deform rather than shear cleanly under excessive hold-down pressure. And short-cut capacity — the thickness you can cut over, say, the first 500 mm of the blade — is usually higher than the full-length rating, which is useful when you only ever shear small brackets.
Step 2 — Choose between swing beam and guillotine
Both designs cut a straight line; they differ in how the moving blade travels and therefore in what they are good at.
| Swing beam | Guillotine (vertical / variable rake) | |
|---|---|---|
| Blade motion | Arc — pivots at the top, swings through the cut | Straight down, with rake angle adjustable |
| Cut quality | Good, with slight bowing on thick plate | Better on thick and narrow cuts |
| Distortion on thin sheet | Generally lower | Higher unless rake is reduced |
| Thick plate | Limited | Preferred |
| Typical use | General fabrication, thin to medium sheet | Heavy plate, structural work, narrow strips |
| Cost | Lower | Higher |
For general sheet metal work — the same shop that runs a 100 t press brake on enclosures, panels and brackets — a swing beam shear in the 4–6 mm class is normally the better fit. Move to a guillotine when you are routinely cutting plate thicker than about 8 mm, or when you need narrow strips cut without deformation.
Step 3 — Get the blade and the gap right
Blade gap is the clearance between the upper and lower blade, and it is the setting that most affects edge quality and blade life. Too tight and the blades rub, generating heat and wear; too loose and the material tears instead of shearing, leaving a burr and a work-hardened edge that bends badly later.
A practical starting point is roughly 7–10% of sheet thickness, adjusted upward for softer and more ductile material:
| Sheet thickness | Starting blade gap (mild steel) | Effect if set too tight | Effect if set too loose |
|---|---|---|---|
| 1.0 mm | 0.07–0.10 mm | Blade rub, rapid wear | Heavy burr, torn edge |
| 2.0 mm | 0.14–0.20 mm | Blade rub, heat marks | Burr, edge distortion |
| 4.0 mm | 0.28–0.40 mm | Overloading, chipping | Rough fracture face |
| 6.0 mm | 0.42–0.60 mm | Blade chipping | Poor edge, extra finishing |
| 10.0 mm | 0.70–1.00 mm | Blade damage | Severe burr, bowing |
Blades themselves come in two practical grades: carbon-chrome tool steel for general work, and high-alloy tool steel or HSS for stainless and high-tensile sheet. Blades are four-edged and can be rotated and re-ground, so the cost of ownership depends heavily on how often they need re-sharpening — which in turn depends on how disciplined the gap setting is.
Set the gap per material, not per machine
The most useful maintenance habit in a shear is a written gap table posted at the machine, with the setting recorded against each material and thickness you run. Shops that do this routinely get two to three times the blade life of shops that leave the gap where the last operator left it.
Step 4 — Decide the back gauge and control level
The back gauge does for a shear what the X axis does for a press brake: it converts a manual layout job into a positioning job. Three levels cover nearly all requirements:
- Manual back gauge with a hand wheel and a scale. Acceptable for one-off work only. Every cut is measured by hand, and repeatability depends on the operator.
- Motorised back gauge with digital readout. Programmable stop position, single-axis. The practical minimum for any shop doing repeat work.
- CNC back gauge with program storage. Multi-position cutting sequences stored as programs, so a nested job runs as a sequence of stops instead of a series of manual moves.
The choice follows your batch profile, not your budget line. If you cut the same families of parts repeatedly, the CNC back gauge pays back faster than almost any other option on the machine.
Step 5 — Match the shear to the rest of the line
A shear exists to feed something. Before specifying, work out the downstream requirement: what blank sizes and edge quality does your press brake need to hold its bend tolerances? If blanks arrive out of square, the brake will produce inconsistent bend lines no matter how precisely the ram is controlled.
Support and handling matter as much as the cut itself. Front support arms, a square stop, and a rear sheet support prevent long blanks from sagging into the blade during the cut — a frequent cause of bowed edges on 3 m work. For anything wider than the operator can comfortably handle, plan for a lifting aid or a second operator rather than discovering the problem with a damaged blade.
Our shearing machines are specified against the same part lists as our press brakes, so the two machines are sized as a pair rather than independently.
Buying checklist
- Maximum thickness and maximum length stated at a named material — not a single headline number.
- Whether stainless or high-tensile will be routine; if so, size for it.
- Maximum cut thickness if you only ever shear short widths.
- Swing beam or guillotine, justified against your thickness range and cut shapes.
- Blade material grade and whether the gap is set automatically or manually.
- Back gauge type: manual, motorised, or CNC with program storage.
- Hold-down configuration and front/rear support for your longest blank.
- Blade life expectation, re-grinding intervals and spare blade availability.
- Safety: light guards or physical guards, emergency stop, and operator training.
FAQ
Can I cut stainless on a machine rated for mild steel?
Usually at reduced thickness. Stainless needs roughly 1.4–1.6 times the force of mild steel, so a 6 mm mild-steel-rated shear typically handles around 4 mm stainless over the same length. Confirm the derated capacity with the manufacturer rather than assuming it.
Do I need a CNC back gauge on a shear?
Only if you cut repeat production batches. For one-off and repair work a motorised gauge with a digital readout is enough, and the money is better spent on blade quality.
Why does my sheared edge have a heavy burr?
Almost always blade gap set too wide, or a worn blade. Check the gap against your material and thickness first, then inspect the blade edge for rounding before changing any other setting.
WILAMAC supplies shearing machines and press brakes sized against real part lists, together with the tooling that keeps both machines productive. Send us your thickness range and longest cut, and we will confirm the capacity and control level that fits the work you actually run.
