How do I cut vinyl, leather, or gasket material with a drag knife? (Drag Knife Toolpath gadget)

What it does

A drag knife is a free-swiveling blade holder that rides in the spindle (spindle off) and lets a CNC cut sheet goods like vinyl, leather, cardstock, and gasket material. The Drag Knife Toolpath gadget (Gadgets menu) converts your selected vectors into a centerline profile toolpath and, crucially, inserts small swivel moves at corners so the trailing blade rotates to face the new direction instead of tearing the material.

The form

• Blade Offset: the distance from the blade tip back to the holder's pivot center. Use the value from your knife's manufacturer; this is what makes the swivel geometry correct.
• Tolerance Angle: the corner threshold. Direction changes smaller than this angle are cut through without a swivel move; sharper corners get one.
• Cut Depth: final depth, defaulting to the current material thickness.
• Swivel Depth: during a swivel the blade retracts slightly to this shallower depth, staying engaged in the material while minimizing the mark the rotation leaves on the surface.
• Passes: divides the cut depth across multiple passes; useful for thicker leather or gasket stock.
• Use Vector Start Points: when checked, cutting starts at each vector's existing start point and assumes the blade begins parallel to the positive X axis; unchecked, the gadget picks sensible start locations itself.
• Feed Rate / Plunge Rate: travel speed through the material and descent speed. Confirm they suit your machine and material before running.

Safety warning

The documentation is explicit: make sure the spindle is switched off when machining with a drag knife. A spinning drag knife is dangerous and ruins the cut.

Pro tips

• Dial in Blade Offset by cutting a small test square: rounded or flared corners mean the offset is wrong.
• Deep single passes drag and stretch soft materials; several shallower passes cut cleaner.
• Tape or vacuum the sheet down well; drag knives push material sideways more than routers do.
• Official documentation: Drag Knife Toolpath