While I was fiddling with the acceleration settings on my Printrbot JrV2 to get less shaking and perhaps more accuracy, I discovered that reducing the acceleration below 1000 mm/sec^2 pretty reliably caused the machine to stop working  partway through a print. (I can imagine Marlin getting into a situation where it can’t look ahead enough moves to get the acceleration numbers down and quitting in disgust, but that’s probably not the reason.)

So I figured “Two years since the last firmware update, maybe it might be time,” and borrowed my spouse’s MacBook, because there’s a really cool app for OS X that gets the right file for your particular printrbot, handles the twiddly DFU syntax and generally reduces cognitive load.

And then this happened: Everything displayed fine on Repetier’s layers-in-progress visualization, but the result was, er, not exactly the alien my 7-year-old has come to know and use in games.

So I whipped up a 20x20x10mm calibration cube in openscad and printed it. Hmm, just shy of 25mm on a side.  The M501 command to list settings tells me that X and Y steps per millimeter are the 80 standard for a JrV2, but apparently my JrV2 isn’t quite standard (and since it was kindly calibrated at the factory after assembly, who needed to know?).

A few micrometer checks of Y travel later, it looks like steps/mm is about 62.99, which looks suspiciously close to the number listed on Printrbot’s site for the JrV1. Did someone have a few old pulleys in the bin? Do I really care, as long as I can get the right number dialed in?

But I have to say, once I do get the right number I’m probably going to go back to the scale control in Repetier and make some more fat Marvins. They’re kinda cute.