Hi MadTooler,

My expected tolerance of a gantry router would be +/- 0.003" for position repeatable for a sloppy system. I would think 0.01 at cut would be extreme, although, with the types of diy routers a lot of users tinker with, that is probably a dream to be that accurate. All that aside, I can fairly easily keep the follow error under 20 encoder units (0.001") with a move of 50,000 and infinite jerk, but was hoping to be under 6. I am just not sure if I am expecting too much or too little of the system.
Seems pretty accurate for a large router. You might put a dial indicator clamped to the table and measuring to the spindle. Then apply like 1 lb of force to the Spindle and measure how much it deflects. I'd be surprised if you don't get a few thousands of an inch deflection.



For the Bode plot, what magnitude and frequency should I measure?
Any low frequency (ie 1Hz) can be used as the idea is to lower energy of the high frequencies. Then increase amplitude until you get significant movement. You might read this.