pulsing chatter

[ihavenofish]

so, i was testing out a 1/2" end mill in some aluminium. its a cheapo chinese hss 4 flute. it was performing ok on surface cuts, but poorly on side cuts of any depth. according to my calculator, the cut should have been way within the spindle limits.

so i took out a $40 maritool 4 flute tialn 1/2" variable flute cutter. made a massive difference. but i think it exposed the true issue.

i was pushing a cut of .5" wide, .25" deep, 5000rpm, and 2ipm. the calculator said i could do 10, but i didnt trust it.

at 2 ipm, the motor was not bogging at all, but there was a pulsing in the cut. every few second its would ramp up and then ease off. the theoretical tangential force from the tool is 2 pounds, so the machines rigidity isnt the issue i dont think.

runout/spindle play seems it might be the issue. at 2ipm, the feed per tooth is .0001". my tool in the er25 collet chuck has about .001" runout at the tip.

a feed per tooth of .001" would push the spindle near its limit. does it sound reasonable that the chattering pulses are caused by the feed per tooth varying due to runout? to me this would explain why at higher feeds for shallow cuts there is much less of an issue.