Vibrations during CNC

[JesseK]

Does anyone have a simple way to reduce or eliminate the vibrations the CNC bit causes on a piece you're milling out? We're using C-channel for our side rails of our platform, and we're milling out holes for the wheel wells.

Near the end of the fourth run for each rectangle we cut out, the middle piece that's being cut out begins vibrating. It's not too rough, but it does cause noticable (yet tolerable) imperfections in the cut. Do we have to live with this (and file it down afterwards) or is there a way around it?

Thanks in advance.