The top knife sets the edge quality

On a slitting line the top knife is the one that decides what the cut looks like. It rides against the bottom knife with a small overlap and a clearance set by the holder, and it is the edge that the web actually passes. A top knife that is ground properly and mounted true produces a clean sheared edge. The same knife with a rough edge or a few microns of run-out produces dust, burr and a wandering slit.

What we make

• Top slitter knives — flat disc and dish form
• Dish (male) knives for air-loaded and spring-loaded holders
• Holder-mounted knives to match your existing arbor and locking style
• Matched top-and-bottom sets, ground and checked as a pair

What the geometry has to get right

Outside diameter, bore, thickness and bevel angle all have to repeat the knife you are replacing, because the overlap with the bottom knife depends on them. The bevel is where most of the quality lives: a single bevel is normal for film and foil, a compound bevel holds up better on heavier paper, and the surface finish on the bevel matters more than most people expect. A coarse grind leaves a microscopic saw edge that generates dust on paper and burr on foil.

Run-out is the other silent killer. A top knife that is out of true by a few microns cuts well on one side of the revolution and rubs on the other, so the edge wears asymmetrically and the operator blames the steel.

Where a top slitter knife fails

• Dust on paper or board. Edge rounded, or bevel finish too coarse. On paper lines this is the first sign, not a visible defect in the slit.
• Burr on one side of the slit. Clearance or overlap wrong, or the top and bottom knife no longer match.
• Uneven wear around the circumference. Run-out. Check the holder and arbor before ordering a new knife.
• Edge chipping on foil. Too hard an edge for the material, or contamination in the web path.
• Web wandering between slits. Often tension rather than the knife — but a dull top knife crushing instead of shearing will do it too.

Top and bottom knives are a pair

Clearance is a property of the two knives together, not of either one. If you replace only the top knife, the new edge meets a worn bottom edge and the clearance you set will not hold. We strongly prefer to quote them as a set, and when a customer insists on one half we ask for the bottom knife dimensions so we can at least match the geometry.

How we match an existing top knife

Send the worn knife. We measure outside diameter, bore, thickness, bevel angle and the dish depth if there is one, then check the holder interface. Tell us the web material, its thickness and the line speed: those three determine the bevel and the steel grade far more than the machine brand does.

Top slitter knife questions

Can I replace only the top knife?

Physically yes, but the cut quality usually drops. The clearance is set between the two edges, and a worn bottom knife cannot hold the setting a new top knife needs.

Why is my paper line making more dust than before?

Most often the top knife bevel has rounded or been ground too coarse. Dust is the paper line’s version of a blunt blade. Check the bevel finish and the overlap before changing anything else.

Do you supply the holder as well?

We supply knives to fit your existing holder. If you are changing holder type, tell us the arbor and locking style and we will match the knife to it.