High speed machining

It will be as smooth as any machine with no jerk limiting can be. The biggest problem with Linuxcnc's motion system is that it only does linear acceleration.

I am not familiar enough with the controls in Haas or Mach3 to know what the limiting factors are or what the source of their jerkiness is for you. If it is line to line reading, Linuxcnc with the new trajectory planner should be better. If it is step generation limitations or max feed rates, Linuxcnc with hardware step generation or analog servo should be better. If the limitation is linear acceleration/infinite jerk, it won't be better. Infact if infinite jerk is the problem the old tool planner might give better results than the new planner (if line to line reading isn't to much of a limiting factor)
.

This brings up a question I have had for awhile now, are we talking about closeing the feedback loop through Lcnc or thru just the servo and drive? I was wondered if lets say I retrofitted a HAAS for example, could I more-or-less get the same preformance by closing the feedback loop thru the yaskawa drives (step/dir input)? Then I would not be nearly as dependant on PC latency and jitter? Or do I have than backwards?

If the drives handle the velocity part of the loop, linuxcnc's position loop rates or say 1 to 4 KHz
are fine for high performance.

At some point the chord error (from discrete velocity steps at the servo loop rate)
becomes significant but thats only for rather extreme accelerations.

As Todd mentioned, lack of a low jerk trajectory planner is probably the main limitation

There is ongoing work on a limited jerk TP however so this limitation may eventually be removed

Servo loop jitter is not terribly significant

OK I am using nema 23 steppers direct drive to a funky mm pitch ball screw its about a 5 turn per inch i max out and reliable 60 ipm iam usung pico systems USC with cheap encoders it will run the same code i run in a haas faster and smoother its still not smooth enough but its pretty good i am at 85 ipm acceleration i can get about 100 ipm but with all the weight on my table from fixture i would just tear my machine up and wont really have any time savings

Update i am able to acheive 240 ipm on my mill with steppers with 50 inchs/sec accel i have been running it pretty hard for the past few months Haas should take notes...