Thanks Carl, that is basically what I figured.  So I'm correct to be using it in the 20 V range.  So when I hold the red probe on the trim pot and the black to ground, I'm measuring 0.25.  I guess what I'm asking is what are the units on that measurement and where on my motor data sheet can I find the acceptable range?  I think that is a current measurement.  I know I can run the motor up to 2.0A but I don't want it nearly that high for an extruder.  Is 0.25 a good place to start?  Thanks.

You are measuring Vref, which is the reference voltage the stepper driver uses to work out how much current to pump through the motors. You are measuring it in volts (V), so 0.25 = 0.25V.

If your Vref is 0.25V, then according to the motor driver specification, your motor current is being controlled to 0.5A, which is probably a touch low for that motor. You have room to go up, which is good news!

The more current, the more motor torque (when stopped / moving slowly) - they're approximately proportional. The disadvantage of running the motors with super high current is the heat, noise, and in the case of the extruder, the moire pattern it will put into the  side of your prints (the microstepping becomes uneven).

I'd suggest similar to ward - my method's a bit different though.

(1) Get the extruder all up to temp, filament installed as usual, etc.
(2) Free-air-extrude a few 100 mm's
(3) While it's running, turn the pot down until the extruder starts skipping (clunking, you should be able to see/feel it skip).
(4) Now turn it back up and listen for a groaning noise - it appears gradually, the louder the groaning the more moire you'll get in your prints, but the less likely a skip will be.
(5) Tune back and forth until you're happy with a smooth sound but consistently no skipping (it's a balance!).
(6) Check the voltage when you're done, I guess it's likely to be a bit higher than you have it currently, but hard to say!

The pololu DRV8825 module allows Vref adjustment approximately between 0V and 1.1V, which corresponds to 0A - 2.2A motor current. Your motor will be fine over this range (nothing is likely to happen suddenly if you slightly over-drive it for a short time), so don't be afraid of playing with the Vref pot to get a feel for it. Take some time, get to understand the sound, it kind of makes sense when you listen to it. Think of it like tuning a guitar.

As for whether this causes your splitting issue, no idea haha.

Also, do you agree that my splitting issue is likely caused buy an extruder Vref issue?

Its this one:
http://www.amazon.com/gp/product/B00B7C … ge_o00_s00

That meter is setup with ranges so you do need to know the range the voltage you are checking would be in. The green band on the top left is dc voltage. Its ranges start from top 500 volts. You can measure op to 500 volts. Then 200 volts. Up to 200 can be measured. Then we have 20. This where most voltages for DC on a printer would be meaured. Unless you have a machine that uses 24volts then you would need the 200 range. The next range is 2000m. That is mv or the same as 2 volts. The 200m which would be .2 volts or less.

If it's the same as the pololu module: www.pololu.com/product/2133
Then current per phase I = Vref * 2 (according to the above)
Your motor is rated at 2.0A per phase (according to your datasheet)
So you could potentially run it at up to Vref=1.00V

That said, that's the maximum current setting - it might be hot and not very smooth at that level, but at least you know you can go a bit higher. 2A is quite high for the DRV8825 (it can in theory do up to 2.5A, pololu module max at 2.2A), so make sure you have a heatsink on the chip and a cooling fan for it, or it will probably thermal trip pretty quick much above Vref = 0.5V.

Good luck.

http://www.omc-stepperonline.com/downlo … -2004S.pdf

I'm running DRV8825's on the RUMBA board.  I'll confess I don't know much about the multimeter but it is set to V 20 to get the above reading.  I had it turned down to 0.15 and it skipped at higher speeds so I'm thinking this is a Vref issue.

Both are the same object, and wall thickness and just mirrored.  I am getting a strange splitting issue where it really does it more on one side and almost not at all on the other.

I recently replaced the stock extruder stepper because the hobbed gear had started to slip and it was glued on so I had to replace the whole thing after stripping the set screw.  I had a spare NEMA 17 around anyway.  After this, I did an entire re calibration.  Printing ABS at 245 C, bed at 100 C with a full enclosure.  PID tuned, E steps dialed in, fresh spool of ABS is not old.  Vref on E is adjusted, motor spins smooth without ticking but I might try turning it down even more to the point that it starts skipping, then back up just a little bit.

Any idea what is causing this, why it is primarily on one side, and how I could fix it?  Thanks!