PCB Mill skipping steps? using EMC2

[morrowsend]

I've built a DIY PCB mill and I'm using a HobbyCNC Pro rev1 (I think) driver. I've installed the LinuxCNC Distro and have done the latency testing to get my appropriate values. I am having issues with my steppers skipping steps. I've run several small PCBs, and I always have the issue with my boards getting way off track in a short time, especially when milling the elipses for IC pins.

I can visually see as well as feel the leadscrews skip a step (or more likely quite a few) when an axis is ramping up or ramping down from max speed. It is likely missing more than this, but this is the only time it is noticeable. I am using 60oz.in. Applied Motion Products - 44A501711-001 unipolar stepper motor steppers with 200 steps per rotation from alltronics. I have the wiring correct on these for the motor drive I am using. The motor driver is tuned to those motors as well.

I am hoping someone might be able to take a look at my settings and spot something I am missing. My settings for the EMC2 stepper mill configuration wizard are below. The same values are used for all 3 axis.

5000ns Step time and Step Space
Dir hold and Dir setup = 20000ns

Base period Max Jitter = 18323
MIn base period 33323
max step rate 30009
Motor steps = 200 steps per revolution
No microstepping, so that field is left as 1.0 (Motor driver is set up the same)
Motor : Leadscrew = 1:1
leadscrew pitch = 20 rev/in (standard 20TPI all thread rod with DIY anti-backlash nuts. Don't bother lecturing me on using allthread, I can't afford anything else ATM.)

Max velocity = 0.25in/s
Max acceleration 1.0 in/ S^2

I attempted to reduce the velocity and acceleration values, but this actually made the problem worse. Any help would be greatly appreciated!

[chester88]

I'm no expert on this but i would add microstepping if you can.
The chief advantage of micro setting is smoothness that helps eliminate resonates.

resonates is a real problem for steppers - there are many things done (in the driver) to work around it. You didn't mention which driver your using did you?

[cncbasher]

what voltage and current do you have supplying the stepper motors ?
you need around 36v @ 8 - 10A as an average

what stepper drivers are you using ?

your problem is your running the motors faster than the step rate they are capable of
or just plain miss tuned , or the power supply is not capable of the current .
so at this stage difficult to tell however ...

some stepper drivers default to 1/2 step as the minimum ( leadshine types )
so the stepper multistep should be set as 2 as they are 400 steps

[morrowsend]

My motors are 2.3v, 2.3A. It is actually these exact motors: Applied Motion Products 44A501711-001 unipolar stepper motor | Alltronics

I'm using a modified PC power supply with 12volt output and 34Amps on the 12v line.

I am using a HobbyCNC Pro Rev1 3-axis driving board. I've tuned the driver to the 2.3v motors.

I had tried changing my timings to the ones below, but this actually seemed to make the problem worse:
Step time and Step Space = 6000ns
Dir hold and Dir setup = 30000ns

Again any help is greatly appreciated!

[chester88]

try microstepping.

Hobby pro is capable of 1/1, 1/2, 1/4, 1/8, and 1/16 Microstepping.

[morrowsend]

Thanks for your suggestion! I tested all of the microstepping settings, and I must say, they all provide much better results. It isn't perfect, but it is much better. I think this is because instead of missing a whole step, I'm only skipping fractions of steps, though when I reset to home and run the same G-code, it retraces the prevous path exactly, even though it doesn't produce the results I expect. For instance, I have two half-circles that are drawn at different times which are supposed to mate together to form a whole circle. They don't line up right, and in fact the machine doens't finish drawing the entire second circle before picking up the Z axis and moving on to the next command. The G-code produces the correct results in the preview window in EMC2, but the machine does this incorrectly consistantly regardless of the microstepping setting.

Any idea about this kind of problem?

Thanks again.

[brianpretty]

Have a look here seems to be a common issue with those boards

LinuxCNC Documentation Wiki: HobbyCNC