Shear blade clearance
The one setting that decides whether a cut edge is clean or ragged — how to read the four zones of a sheared edge, and how to diagnose a clearance problem from the burr.
Blade clearance is the horizontal gap between the upper and lower blade at the moment of the cut. It is measured in hundredths of a millimetre, it is the single setting that decides whether your cut edge is clean or ragged, and it is the first thing to check whenever someone says “the machine cuts badly.”
What the cut edge is supposed to look like
A sheared edge is not a single surface. It has four zones, top to bottom:
| Zone | What it is | What it tells you |
|---|---|---|
| Rollover | The rounded lip where the blade first presses in | Grows with too much clearance or a dull blade |
| Burnish (shear zone) | The smooth, bright band cut by the blades | The good part of the edge — its depth reflects correct clearance |
| Fracture | The dull, rough band where the material finally tore | Grows with too much clearance |
| Burr | The ragged spike left at the bottom edge | The clearest indicator that clearance is wrong or the blade is dull |
Read the proportion. Too little clearance and the fracture lines from the two blades do not meet — the material gets cut twice, producing a narrow bright band and a heavy burr, and the blades wear fast. Too much clearance and the material rolls and tears instead of shearing: a big rollover, a small burnish band, a tall fracture zone and a heavy burr. Both ends of the range look like “bad cuts” but they need opposite corrections.
Setting it
Clearance is set as a proportion of material thickness, and the proportion changes with material. Mild steel, stainless and aluminium do not share a setting, and neither do two thicknesses of the same grade. The authoritative number for your machine is the value in its manual or the manufacturer’s clearance table — the figure that matters is the one for your blade geometry and your material, not a generic percentage.
The most common mistake is not a wrong number, it is no adjustment at all.A shear set up for mild steel and then run on stainless for six weeks will produce poor edges and short blade life, and the machine will get the blame. Set clearance per material per job.
How to tell what is wrong
| Symptom | Likely cause |
|---|---|
| Heavy burr, narrow bright band | Clearance too small |
| Large rollover, tall rough fracture, heavy burr | Clearance too large |
| Burr on one end of the cut only | Clearance not parallel across the blade length |
| Edges degrading gradually on unchanged settings | Blades dull, not clearance |
| Cut edge has a second step or a burnished lip | Clearance far too small, or blade chipped |
| Offcut twists badly | Rake and hold-down, not usually clearance |
| Edge quality varies along the length | Blade not parallel, or guide wear |
Getting a parallel gap
Clearance has to be the same from one end of the blade to the other. The practical method is a feeler gauge at several stations along the blade — both ends and the middle, at minimum — with the beam brought down carefully by hand or inching. Adjusting by eye and hoping is how blades get chipped. Machines differ in how the adjustment is made (shims, an eccentric, or a dedicated adjustment mechanism), so follow the procedure in your manual rather than a generic description.
Clearance interacts with the other settings
Clearance does not operate alone. The rake angle sets how much of the blade is engaged at once — more rake means lower force and more twist. Hold-down pressurestops the sheet lifting as the blade enters; too little and thin sheet climbs, too much and it marks. And blade sharpness sets the baseline: a correct clearance on a dull blade still produces a poor edge. When a cut is wrong, check them in that order — clearance, then sharpness, then rake and hold-down.
When to regrind
Blades are consumables. The signal to regrind is a rising burr and increasing cutting force on a setting that used to be right, not a calendar date. Regrinding reduces blade height, which on most machines has to be compensated for — shimmed or adjusted — or the clearance and the cut position both change. If your shear needs noticeably more force than it used to for the same cut, check the blades and the clearance before suspecting the hydraulics.
Frequently asked questions
What is blade clearance on a shear?
The horizontal gap between the upper and lower blade at the moment of cutting, measured in hundredths of a millimetre. It is set as a proportion of material thickness and varies by material. The authoritative value is the one in your machine manual or the manufacturer clearance table.
How do I know if my clearance is too small?
The classic sign is a heavy burr with a narrow bright band, sometimes a second step on the edge. Too-small clearance makes the blade cut the material twice, which raises cutting force and wears the blades quickly.
How do I know if it is too large?
A large rounded rollover at the top of the edge, a small bright band, a tall rough fracture zone and a heavy burr. Too much clearance lets the material roll and tear rather than shear cleanly.
Why does quality drop when I switch to stainless?
Because stainless needs a different clearance and different hold-down from mild steel, and it work-hardens. Running it on a mild-steel setting shortens blade life and produces poor edges. Set clearance per material per job.
How do I check the gap is even along the blade?
Use a feeler gauge at several stations — both ends and the middle at minimum — with the beam brought down carefully by hand or inching. A burr appearing at only one end of the cut means the gap is not parallel.
Does regrinding the blades change the clearance?
Yes. Regrinding removes blade height, and on most machines that has to be compensated by shimming or adjustment, or both the clearance and the cut position shift. Regrind on condition — a rising burr and rising force on a setting that used to be correct — not on a schedule.
Send us your cut symptoms
Tell us the material, thickness and what the burr looks like. We will tell you whether it is clearance, blade condition or a setting — and what to change first.