melted wall using HIPS on TAZ5

I printed a fixture using HIPS material. My settings were 240C extruder, 100C bed, no fan, inside a box, ambient temperature inside box 44C. The whole fixture came out really nice except for one wall that looks like it was melted by something close to it after it was built, but it came out of the printer looking like this. Therefore, it was built this way one layer (.1mm) at a time. BTW, the object is 100% solid too.
Any ideas what might have caused this?

Here’s another view of it. The part did not lift off the bed during the print.

It corresponds with the perimeter start, so it could be an issue with the filament retract and restart. Or it could be some wierd thermal effect. Is there a hot-spot on the bed?

What was the orientation of the part on the bed? When printing HIPS, I would often find defects due to heat buildup on the side of parts opposite the printer fan, the left side of the print. While I never implemented it, I thought adding a fan and shroud on the left side of the extruder may have helped.


I don’t know about hot spots. The part was oriented so that the break was to the back.

If it was printed with the break to the back, then I doubt the issue was related to the problems I saw with uneven cooling like I had.

Perhaps try going to 90% solid, to see if the problem goes away?

Or try a low fan setting – 50% or so?

Either would reduce the amount of heat going into the part, which may be the basic problem. Why it happens where it does I have no idea, though.