Stepper Motors stutter when jogging full speed at a regular pattern.

Hello all I am running a Chinese 6090 cnc and have developed a problem in when I move the machine in a direction this includes xyand z axis the velocity speed has and interrupted sound and pattern.
I turned steppers by hand and no problems there so im concluding pc or mach3 issue .Driver test runs quite uneven .But machine has just developed this problem and was working ok.
Any help would be greatly appreciated Thanks
Mike

Your pc/os or parallel port or cable is the issue

Ive got a pc eith windows 7 that will not pass mach3 driver test

And when using this pc the movement is herky jerky and sounds horrible...once i change pc all is good

Hi,
the parallel port was really the only way for hobbyists to get into CNC years ago.....these days however there are some really good external motion
controllers that are USB, or better still, Ethernet connected, and a lot of the stuttering/stalling that used to occur with parallel ports vanishes. I'm
not saying that you can't get a parallel port to operate properly, but you will always be constrained that it has a fairly slow max pulse output
pulse rate and will often result in stuttering motion at max speed.

If you wish to investigate external motion controllers I would recommend an Ethernet SmoothStepper. I would disgregard all the crppy
Chinese made boards, they seldom work as advertised and often rely on pirated Mach3 software, avoid like the plague.

Craig