I have a Precision Mathews PM25-MV milling machine I converted to CNC. It's been working for a few months now. I'm having a problem with chatter when machining on larger cuts.

Video of said chatter, it's the worst when it gets to left side of this hole in the video: https://www.youtube.com/watch?v=exJE...ature=youtu.be

In this cut I was running a 1/2" 4 flute end mill from Kodiak, 2500 RPM, 6in/min feed, .3" DOC, 0.044" WOC with flood coolant. Machining 1018 Steel 1 inch thick. It chatters a lot worse on one side vs the other when milling this hole.

Any idea what is going on with this? Things to check?