The funny thing about thermoplastic…

… is that it melts when it gets hot.  “Well, duh!”, as my daughters would say.  PLA, the thermoplastic used in most 3D printers, is a very practical material.  It’s light, strong enough for most purposes, and melts at a reasonable temperature.  Which is why I’ve used it for many of the parts in my printer.  Most of these parts have no chance of getting hot, so the fact that PLA softens as it heats up is of no concern.

The one area that does get hot is the area around the hot end (“duh!” again).  This is expected, and the J-head hotend uses a high temperature resistant polymer called PEEK to isolate it from parts made of PLA.  So far, so good.  At normal printing temperatures the (PLA) hotend holder remains cool enough because of the PEEK insulation.  If, however, one accidentally sets the hotend temperature to 2110°C instead of 210°C (no, the software doesn’t stop you doing that) and it takes one a few minutes to notice, then the PLA can get substantially hotter.  Easily hot enough to deform, in fact.  And no, I didn’t let it get to 2110°C – I spotted the problem when the temperature got to about 240°C, at which point I panicked a bit and found the BRS.

The net result is a deformed pair of print head mounting components:

P1000751P1000753

The deformation isn’t hugely obvious (its around the small hole in the middle of the pink part, and on the further prong of the red one), but the net result is that the j-head is slightly loose, and is set at a slight angle to the vertical.  This may help to explain why some (but not all) of my prints are slanted.  I suspect that the print head offers more resistance to movement in one direction than in another, and this manifests itself in a number of missed steps on one of the stepper motor axes.  Each layer may thus be slightly offset from the previous, leading to the slant.  Objects which do not require many movements in the ‘difficult’ direction have fewer missed steps, and print more vertically.  Perhaps.  This is only speculation.  Rob’s printing me a new head (that sounds weird), so I’ll see if the result is straight prints.

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