Controlling the 4th Motor on MiniRambo

[jeffeb3]

This is going to be tricky. My impression is that it is a little bit like the tangential cutter problem, where we were trying to move a 4th axis so the razor blade was always parallel with the path. This thread is long, and we go back and forth on how we should do it. But it may give you an idea of the magnitude of the problem, and maybe there are some working steps.

Tangential cutter in development

Some people may have seen where a few of us hijacked a drag knife thread to talk about hardware off topic. Sorry OP. I was able to remix a drag knife to increase the offset by a couple of mm’s, which effectively enabled me to cut lots of circles in 7mm double wall cardboard pretty reliably. Useless for anything with corners because the huge offset trashes the minimum radius of cut. The answer for thicker material seems to be a tangential cutter. I thought I would share my progress working o…

Here is how I would break this problem down:

1. Switch to the mp3dp firmware for the mini rambo. Get it at MarlinBuilder releases. V510, V13DP_MiniRambo. Open it in platformio and compile it, then flash it. This won’t change much, but you will have proven your tools work.
2. Disable the temperature checks (I think it is something called cold extrusion) or just change the thermistor to the 999 dummy and the dummy value to 175. With this flashed, you should be able to send commands like G1 E10 F300 and see the E motor turn. The steps/unit need to be changed to be steps per degree.
3. The hardest part is generating the gcode. I think the easiest way is probably to write a script (I know) that will take in the XYZ gcode and predict what values for E you would need. Then output a file with the E values set on each movement command. I remember talking a lot about that on the tangential cutter thread, but I don’t remember how far it got.