Trouble in paradise....Pronterface and Ramps 1.4

Hey everyone,
Please take a look at the photo I've attached. Print starts out fine and is very detailed but then it almost looks like the filament gets too hot ...I thought at first that the thermistor was reading incorrectly and the pla was overheating. I turned down the temps and actually can get the pla to flow at about 150. However, I placed a thermometer on the hot end and found that the temperatures were within 3 degrees all the way to 175 degrees. Has anyone had a similar experience ?? I'm printing with a mendel reprap, ramps 1.4 electronics and pronterface software.

Different PLA extrudes best at different temperatures, due to both the composition of the plastic and the effects of the colourants. Sometimes even batch by batch from the same supplier.

You don't say what temperature those objects were printed at. 175 degrees is way too hot for the filament I use, on my MakerGear Prusa. I can extrude some PLA at 150 Celsius, though I get striations in the surface that I can see under a microscope. I usually print at an indicated 160 Celsius, with clear PLA, and that gives me smooth extruded filament.

My guess is that you have a low-temperature PLA filament. Keep turning the temperature down until you can't extrude reliably, then turn it back up again a bit (maybe 5 degrees?) from there. If you are printing fast, you may need to set the temperature higher to get it to flow through the melt chamber fast enough, but it sure doesn't look like that is your problem.

Also, PLA needs a fan! Otherwise the heat builds up as the layers build up, and without a fan it all gets too soggy. Corners lift and the extruder nozzle jams on raised lumpy bits. If you forget to turn the fan on until _after_ things have got raised and lumpy, you are guaranteed layer offsets as the suddenly cold plastic blocks the movement of the nozzle (speaking from personal experience...)

In summary, lower the printing temp to 150 or 155 degrees since you say you can extrude at 150. Stick a desk fan where it blows over the print bed all the time (or turn it on after the base layer has printed).

Good luck. If this fixes your problem, consider submitting the before and after photos and an explanation of how you fixed it to one of the pages that catalogs printing mistakes, so others can learn from your experience. Those are really dramatic melty objects!

thanks for the suggestions. I was wondering about using a fan. I'll give it a shot.