Question First cut a disaster

After finally getting the machine to go where I want I tried cutting a basic 2.75 dia. circle out of 6061 T6 aluminum. I quickly snapped three 1/8 end mills and 1 1/8 ball nose mill experimenting with different feeds and speeds...My plunge rate and cut depth were off at first but next, trying a 1/4" end mill the result was terrible. The machine starts chattering and jumping all over the place....I notice some place in my Z axis....Not sure if it's from the chattering or if it was that way before.....I hope I can figure out how to cut aluminum with this thing.

Aluminium and plastic are the most difficult materials.

You should slow down the spindle speed. I always use max. 5000 rpm and cut deep per cycle 0.02 inch (0,5mm).
Also I ever use a mixture of water, ethyl alcohol and washing-up fluid for cooling...just some drops to keep it wet (hope I found the correct words... ).

It is important that the end-mill will cut the material. If the spindle speed is to hight it will rub the aluminium, getting hot.

(not my video...)