Hi David On Saturday 17 March 2007 22:20, David Szakovits wrote:

i have a small mill with stepper motors, gecko drives running EMC1 (with quickstep).

yesterday, i decided to try gcode for the FIRST time and try machining some wood.  i used the rectpocket program from http://jelinux.pico-systems.com/gcode.html to generate gcode.  when i first ran the generated code, i received  a "following error" message.   the first move in the gcode was F40 and i changed that to F20.   after that, i did not see any additional error messages.

A following error is usually an indication that max velocity is set too high in the ini file or, depending on which driver you're using, PID gains.

maybe i have some tuning problems or perhaps this is normal behavior for a modest machine.  i don't know.  here are some dumb questions:

should a small system be able to reliably execute moves like f40 or so? what is a "following error" and is it fundamentally different than a missed step?

A small stepper driven machine like a Sherline should be able to do 12ipm, and although it is possible to use small servos and push this beyond 24ipm, I wouldn't recommend it - These small machines were designed to be hand operated, running under CNC control allows you to accelerate the wear, and loadings at higher speeds make things worse. Keeping maximum velocities and accelerations down to modest levels improves the lifetime of the machine.. A lost step results from mechanical loading exceeding the capabilities of the stepper motor - It can also be the result of timing issues on the parallel port with respect to setup & hold times - A following error occurs internally as a result of acceleration and/or velocity limits being exceeded.. Depending on how fast the machine decelerates to a full stop after a following error is triggered, steps may be lost, or with enough mass on the table, even gained. However... Large F values should be clamped internally to limit the maximum velocity, so if the system is set up for 20ipm, commanding a move at 40ipm shouldn't generate any errors - It would just move a little slower than expected. Regards, Paul.