Colorfabb XT, over extrusion on long straights

I received some Colorfabb XT on Friday. The first parts I printed with it turned out great; these were printed at 200 microns 235C extruder and 70C bed.



Even the bridging was fantastic. I was really pleased so I set about printing a large flat piece and then my problems started. Straight away the first layer develops large blobs and strings. I re-tightened the heatbreak on the hot end to ensure it isn't leaking though there was no sign of a build up of plastic which would indicate a leak. It didn't improve.

It looked like over extrusion so I decided to lower the extrusion multiplier in MatterControl. This produced some improvements. This photo shows the blobs with the extrusion multiplier set to 0.8 (nozzle temp this time was 245C):



So I continued to experiment with the extrusion multiplier. I got it down to 0.4, which lays a really nice first layer, the problem is this only seems to hang true for long continuous paths. Any details which require frequent changes in direction come out under extruded. This photo shows the first layer with a 0.4 extrusion multiplier; it doesn't show up too well in the image but towards the corner, where the head is changing direction more quickly the width of the extrusion becomes narrower and gaps appear.



If I print a small model with at this setting it is also under extruded. So I seem to be stuck between over extrusion on long continuous paths or under extrusion on smaller or more detailed models. I've attempted to reprint this part maybe a dozen times but I can't figure out what setting might solve my problem.

My settings are:
layer height: 200 micron
first layer: 300 micron
speed 35mm/s for everything
first layer speed : I've experimented with values between 50% and 100%
filament diameter: 1.68mm (measured with caliper)
extruder temp: 245C
bed temp: 70C

Any pointers?

 

Thanks Mark. I bumped the nozzle temp up to 260C and it does seem to have helped. In the photo the section furthest away is printed at 260C, 25mm/s, it is significantly improved though far from good. The inch or two nearer the camera is near perfect, it's the same settings but slowed down to 12.5mm/s. There is still a little bobbling which can be seen near my thumb.

I still feel like I'm missing a part of the puzzle here. I've just set it going on a painfully slow print so I'll see if I have any success. I've also contacted ColorFabb for support.