Posts Tagged ‘ melt

Building the C-Bot 3D printer: Part 25 : Catastrophic failure

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I figured at some point something would go wrong:  It finally did.

I’d noticed the stepper for the Bowden extruder had been running really hot.  Hot to the touch, and way hotter than the other steppers.  I had started by setting it’s reference voltage to .6v (like all the others), but it didn’t have enough ‘oomph’ to drive the filament through the extruder.  So I increased the voltage until it started behaving, which ended up being around 1.2v (2x as much as recommended…).  I’m sure this contributed to the over-heating.  But I wasn’t sure what else to do:  Any lower voltage wouldn’t extrude properly.

I’d been pointing a small fan at the stepper, and this seemed to keep it’s temp at a reasonable (but still hot) temp.  And since things had been going so well I decided to do my first “big print”:  Fired it off, and for the first 20 minutes all was well.  I decided to take a walk.  When I returned an hour later, to my surprise it was air-printing:  I found this really surprising with a Bowden (heat-creep on my Replicator 1’s direct-drive can cause this more easily).  The Bowden stepper was still turning, so I figured some how it had notched the filament.  But there was no notch, it just wasn’t extruding.  That’s when I noticed this:

melty_bend2

Top view, looking ‘down’.

 

When I went to touch the stepper, it was burning hot:  I had forgot to turn on my cooling fan, and the stepper had gotten so hot it melted the printed Bowden mechanism :(

The great thing about having two printers is you’re always able to print, even if one breaks:  I re-printed the melted bits and after two hours bolted them back on.  But I obviously still needed to do something about the heat.  I was perplexed why this one stepper needed 2x the voltage of the others.  So using the techniques mentioned before, I reset the reference voltage on the DRV8825 back to .6v, and tried extruding:  I worked fine.  Huh?

I’ve noticed while building this bot that stuff like this often happens:  I’ll set some value that doesn’t seem right, but works.  A day later, I’ll reset it to the ‘correct’ value, and then it works as expected.  I don’t know how to explain this, but it’s not the first time it’s happened.

But it’s printing great now:  I’m an hour back into the ‘big print’, extrusion is good, stepper is ‘normal temp’.

Live and learn!


 

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