The station in the illustration is the shear of a busbar processing machine: a heavy C-frame, an upper blade holder above a lower blade, hydraulic hold-down clamps on both sides of the cut and a thick copper bar fed in over a ball-transfer table. The machine's force rating says how big a bar it can cut; the edge it leaves depends on blade clearance, sharpness and clamping, and that edge becomes a bolted joint carrying current.
Covers the shearing station of busbar processing machines and stand-alone busbar shears for copper and aluminium bar: blade clearance as a percentage of thickness, edge zones (rollover, shear, fracture, burr) and work hardening, effects of clearance errors, hold-down clamps, blade overlap and the resulting lead and tail off-cuts, shearing versus sawing, and edge acceptance checks. Machine sizing, stations, positioning and bending for whole busbar machines are on Busbar processing machines; turning, regrinding and setting the upper blade of plate guillotine shears is on Upper blade for a guillotine shear; shear-beam load cells are outside this page.
CNFX editorial research · Sources checked October 13, 2026 · 3 sources
Durma, a shear and press-brake maker, sets blade clearance as material thickness × a clearance percentage chosen by material and thickness, as a starting point before the machine maker's own value.
Durma's worked example is 5 mm mild steel at 6%, a 0.30 mm gap. Too small a clearance gives secondary shearing and rough edges and can chip the blade; too large gives tearing rather than clean shearing and excessive burrs; uneven clearance along the blade gives an uneven cut.
Copper is not in the chart. For a 10 mm aluminium bar the chart gives 0.5–0.6 mm; at the 8% relative clearance studied for copper below, a 10 mm bar would be 0.8 mm (Editorial calculation).
Material (Durma chart)
Thickness
Clearance
Mild steel
≤ 3 mm
5–6% of thickness
Mild steel
3–10 mm
6–8%
Stainless steel
≤ 3 mm
6–8%
Stainless steel
3–10 mm
8–10%
Aluminium
≤ 3 mm
4–5%
Aluminium
3–10 mm
5–6%
High-strength steel
≤ 10 mm
8–10%
The copper figure is an editorial extrapolation from a thin-sheet study, not a recommendation. Ask the machine maker for its clearance setting for your copper and aluminium thicknesses and how the gap is set along the blade.
02
What the cut edge shows
Ouyang and co-authors (Advances in Manufacturing Technology XXXI, IOS Press) sheared 0.5 mm copper sheet at different clearances and measured edge shape, work hardening and force.
As clearance increased, the burnished shear zone became shorter while the fracture zone, rollover and burr all grew. Work hardening at the edge first increased and then decreased, peaking in both hardness and depth at a relative clearance (c/t) of 8%; along the edge from the rollover side to the burr side, hardness rose and then fell, highest at the boundary between the shear and fracture zones.
Payapress, a busbar machine maker, describes the same sequence on bar: the metal passes through rollover, burnish, fracture and burr, and burr height rises with poor clearance and dull blades. It recommends defining an acceptable burr height and squareness, checking them with simple go/no-go checks, and standardising deburring by brushing or light face milling, because consistent burr-free edges support contact pressure and lower thermal risk at joints.
Clearance increases (Ouyang et al., 0.5 mm copper)
Effect
Shear (burnished) zone
Shorter
Fracture zone
Taller
Rollover
Larger
Burr
Larger
Work hardening
Rises, peaks at c/t = 8%, then falls
The study used thin sheet; behaviour on 10 mm and thicker bar should be confirmed by trial cuts. Ask for macro photos of cut edges on your bar sizes and a stated burr height and squareness.
03
Clamp land, blade overlap and off-cuts
Payapress explains why even shears sold as burr-free need lead and tail off-cuts: the hold-down clamps must press on the bar to stop it moving, and the length under the clamp becomes off-cut once the part is separated; the blade needs overlap to finish the cut; and a short crop at the start and end removes deformed zones to reach squareness and edge-finish targets.
It compares methods: shearing is fast with minimal kerf but can leave rollover and burr if clearance is off or tooling dull; sawing removes a blade-width kerf and is slower but leaves a cleaner 90° face, which may cut rework on critical lap joints. Off-cut waste is reduced by correct clearance and sharp blades, accurate stops or CNC back gauges, nesting the cut sequence, and cropping a starter piece before the first customer part.
Method (Payapress)
Why off-cut is needed
Edge after cut
Shearing
Clamp land and blade overlap; shear zone forms
High throughput; burr and rollover if clearance or edges are off
Sawing
Kerf removes material; fixturing still needs approach
Cleaner 90° face; wider kerf; slower
Punch-cut on integrated lines
Die entry/exit and clamping
Controlled; verify burrs
Ask the supplier to show the clamp design and the required lead and tail length, blade steel and resharpening interval, and length repeatability on three consecutive pieces, as Payapress suggests.
04
What to give a supplier about the shear station
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
State bar materials and tempers, widths and thicknesses, required length tolerance, squareness and maximum burr height, joint type (lap joints need flat, square edges), annual cut count and acceptable off-cut length. Ask for blade clearance settings per material and thickness, blade material and resharpening interval, clamp design and lead/tail length, sample cut edges on your bar, and whether sawing or a deburring step is offered.
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
How is shear blade clearance set?
As material thickness × a clearance percentage: Durma gives 5–6% for aluminium 3–10 mm and 6–8% for mild steel 3–10 mm, as starting values before the machine maker's own setting. [2]
What does too much clearance do to a copper edge?
In Ouyang et al.'s copper sheet tests, larger clearance shortened the shear zone and increased fracture zone, rollover and burr. [3]
Why does a busbar shear leave off-cuts?
Payapress explains that the clamp land, blade overlap and crop needed to remove deformed zones all become off-cut, even on burr-free machines. [1]
Shear or saw for busbar?
Shearing is faster with minimal kerf; sawing is slower with a wider kerf but a cleaner 90° face, useful for critical lap joints (Payapress). [1]
Sources and what still needs a direct check
Sources checked 2026-10-13. A busbar machine maker's note on cutting, a shear maker's clearance guide and a peer-reviewed copper shearing study.
