Close

Drag Knife

A project log for Homebrew CNC Experiments

Building a machine with mostly repurpose-able parts.

tedTed 12/20/2020 at 19:560 Comments

I furnished a drag knife from some available parts (hence using the odd 1.5x2.25"  piece instead of a 1.5x1.5" piece). At first I tried using a "swivel hub" which I thought would be perfect, but doesn't move nearly smoothly enough under the loads of the drag knife. So I switched to flanged axial load ball bearings holding a shaft with spacers and collars on each side. I have some trust bearings too, but opted not to add them, as no commercial designs seem to use them, so the load must not be too much.

I used bCNC's Drag Knife plug-in to generate paths for it. (Note to self: surface height of material properties is the depth of cut used)

It works...mostly. The squeeze on the blade isn't quite enough, and eventually it falls out of place. The drag distance isn't fixed/certain so getting sharp corners is tricky. And it's completely useless in corrugated cardboard.

I decided to 3D print a small part to attach to the Actobotics hub. This makes the drag offset more stable and it won't wiggle out of place.

Cutting paper works pretty well - you can see the sharp edges above. Cutting thin (~2mm) craft foam work well, using a 1mm lift swivel height. Cutting even non-corrugated cardboard does not work well - there isn't enough rigidity right now.

I suspect for corrugated cardboard and thicker craft foam, I'll need to try my hand at a tangential oscillating knife, or write a gcode post-processor to do the stabbing.

Discussions