Strange Speed Discrepancy on Curves - LINUX CNC

[m_c]

If the correct speed is maintained during G2/3s, and not using G1s, then the problem is likely to do with lookahead/smoothing settings, or even lack of processing power.

Lookahead would could cause the problem by the motion buffer simply not being kept full enough, so you end up with speed being restricted by the buffer not having enough stored motion to keep speed up. Simple test is to increase the lookahead setting. Lack of processing power would also cause similar symptoms, as motion is slowed to allow the buffer to be filled.

Smoothing/Corner settings would cause the problem due to the trajectory planner restricting speed to remain within the smoothing/cornering settings, at each corner between g1 line segments. It could be the amount of allowed deviation is too low, so the trajectory planner has to run at a slower speed to remain within the permitted deviation from the specified G-code path, while meeting acceleration settings.
Rather than me explain it poorly, have a read of this article in the dynomotion wiki that explains the problem far better, and how to solve it while using KMotionCNC. I'm sure LinuxCNC will have similar settings (KMotion uses the old EMC interpreter, however I've got no idea how much it's been modified and now varies between KMotion and LCNC) - http://www.dynomotion.com/wiki/index...ng_Noisy_GCode