CNC Drag Knife Upgrade With Off-the-Shelf Blades

Drag Knives seem to be the overshadowed awkward kid on the playground of CNC equipment, but they have a definitive niche making stencils, vinyl stickers, and paper cuts. Unfortunately, the drag knife blades for CNC routers are pricey — over $100 for a single blade. [Brian] at the Grunblau Design Studio took the price point as a challenge to build his own end-effector. A few iterations later, he’s created his very own drag knife blade tool that accepts replaceable steel blades for cutting.

From constraint-driven concept, to a 3D printed proof-of-concept, to a fully machined aluminum prototype, [Brian’s] efforts hit all the highlights of a well-engineered project. At the end of the day, dull blades can be swapped for a few dollars, rather than shelling out another $150 for the off-the-shelf variant. We’ve seen bootstrapped CNC vinyl cutters before, but nothing that takes an original re-envisioning of the tool itself.

20 thoughts on “CNC Drag Knife Upgrade With Off-the-Shelf Blades

      1. I agree with you there. Was more stating that the contractual author for hire of this post did not fully research their post, pretending by omission that this post was about a contemporary item and not understanding the difference between a CNC knife holder and the knife that goes inside it (nor correcting it, eight hours later). The item itself is actually clever and cost effective, though certainly not novel. Additionally, oscillating knives are generally better overall, for finer detail work and cleaner cutting.

        http://www.buildlog.net/blog/2010/07/tangential-knife-cutters/

        Here’s a similar drag knife project from just about six years ago, for example.

      1. So if you have a spindle motor without permanent magnets like ,say, an asynchronous motor, or a universal motor, then you are good to go. Those two types are used very often on CNC routers. (vfd watercooled or repurposed trim router).

        1. I think you’d still have an issue with all the rotational inertia. Notice how quickly the knife changes direction when going around a corner. I’d worry that trying to spin and stop a spindle rotor would make it too slow.

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