I was setting up a fourth stepper for the 3D printer extruder. I was using Mach3 as a test controller. I decided to play with tangential knife control while I was at it.
Tangential knife cutters rotate the knife while cutting, so the blade is always pointing in the direction of travel. They work much better than drag knives, especially on thicker materials like gasket material.
It took me a little while to figure out how to setup the resolution for the A axis (I am not a lathe guy) . You set it up as steps per degree. My setup is 200 steps/rev * 10 microsteps/step / 360 =
5.556 step/degree. You then tell Mach3 to use tangential control and set a few items: Lift Angle and Lift Z. When the knife needs to turn at a corner the z lowers the Lift Z amount. It does this any time the corner angle is less than the Lift Angle, so it does not retract at small angles. I left lift angle at 45 and change. the Lift Z to 0.05
I only simulated this by setting the knife stepper next to the machine with a little paper knife taped on, but it all worked as advertised. The only issue is that Mach3 reverts to exact stop mode in tangential mode. This means that things like ellipses are going to be really slow. If you don't need anything but lines and circles it should work at a decent speed.
I might make a carriage for this and create a video of it in action.
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