Parameters: 18,000 RPM, 1,200 mm/min feed, 0.5mm stepdown, 1.2mm stepover (20%), climb, mist. Chip load 0.033mm/tooth, dead center of the manufacturer’s range. Floor finish is mirror-clean, so the toolpath is sound.
Symptom: walls show a 2 to 3mm pitch wave on the left side only, worsening below 6mm depth. Right wall is fine. Identical toolpath both sides, so don’t blame my G-code.
My suspicion: climb milling on the left wall pushes the tool into stock, and with 12mm stickout the deflection shows. But I want measurements, not guesses. Has anyone dial-indicated spindle runout and gantry deflection on these frames under lateral load? If your router holds Ra 1.6 on aluminum walls, post your exact RPM, feed, stepdown, and stickout. I’d take measured numbers over “works fine for me” any day.
Hang on. On that left wall, is it being cut along X or Y? And when you climb mill the left wall, does the tool get pushed toward the frame or away from it?
Broke a 4mm endmill on a 6061 pocket last week off a bad work offset, and the feed felt wrong on one side the whole time. If the axis explains that, a lot suddenly makes sense.
Do you actually have gage readings for the spindle runout and the lateral gantry deflection, or is that still a hunch?
I ran a steel-frame router with 20mm ballscrews like yours, cutting 6061 pockets 12mm deep, 6mm 2-flute with 11mm stickout. Left wall chattered and the right didn’t. Turned out the X-axis gibs on the left were torqued 15% looser than the right. No tool deflection at all, just the axis flexing when the climb mill push loaded that loose gib.
Dial-indicate the gantry while you cut the left wall. Lock the right side, put a dial against the left gantry leg, and see if it moves more than 0.01mm under load. That’s the number that settles it.