Tangential knife add-on for a router

[Alex B]

My brother and I recently purchased an Acorn/ClearPath powered Avid 4x4 router, primarily to machine foam mold patterns for composites. After we had gotten the machine into the shop we started having intrusive thoughts about how to automate some of the more tedious tasks we have in front of us. As mentioned, we’re doing a lot of composites work. This includes templating and cutting tons of carbon fiber fabric. We decided to try adding a tangential knife to the machine to convert it into a DIY ply cutter.

I designed a mounting bracket for an additional ClearPath servo motor that can back-drive the spindle via a timing belt. The spring-loaded blade holder is made using a 13mm THK ballspline and a 3D printed bearing block. All the other mechanical bits are from McMaster. We’re using the spindle as the toolholder since the ClearPath can’t cope with the axial loads. This has the added benefit of not requiring any additional shafting or X/Y tool offset weirdness. Both the motor and homing switch are wired to the Avid controller’s A-axis ports, with power Y-cabled off the X-axis servo. My brother is a coding wiz and found a tangential knife post processor for Fusion 360 on GitHub that he ended up re-writing and customizing to work with the Acorn. The rotary homing scripts in CNC12 also required some minor mods to make them work with a C-axis instead of an A-axis.

The lever handle on the left clamps the whole C-axis assembly onto the nose of the spindle motor and lets us attach and remove it as a unit without messing with spindle tram. There’s also a stop collar to index the mount axially and a dowel pin that acts as a rotational stop. Having good repeatability was important to make the home offset consistent when the machine starts up

Video of the first test cut:



We have since added a 48"x48"x0.093" LDPE sheet as a cutting surface. That’s backed by a sheet of mild steel. This way we can simply hold the cloth down with a few magnets. It's certainly not on par with a real conveyor belt/vacuum hold down ply cutting table the pro's use but for two guys in a garage and a few hundred dollars in eBay and McMaster parts it sure does the job well.

Here's a link to my brother's GitHub page that documents the tangential knife post for Fusion360 if anyone is interested in the same capability:

https://github.com/basketofkittens/tangential-knife

[martyscncgarage]

Nicely done. Thanks for posting your work and demo video.