A lot of the X gantry flex is in the Y rails. A quick 30 minuet mod made a huge difference.
Also like everyone else is saying, fast and shallow is the way to go on aluminum. Good luck
I usually go by the size of the chips, if im getting dust with a 1/4 or 1/8 bit then its definitely too slow. You should be getting a nice small chip with 0.25 DOC. Also, after running something like a 15min job i check the endmill’s temp to make sure its not hot enough to burn you.