Problems with solid base layer of print

Hi,

New to the 3d printing arena. Bought my 1st reprap about 1 month ago and since then I have been calibrating and calibrating and calibrating with no real end in sight to a perfect part. I have gotten a few nice parts but never consistent. I downloaded a calibration set and those files print very good. 0.5mm perimeter box is exactly 0.5mm perimeter and so on. The perimeters are perfect, flexible and does not tear apart. However when I go to bigger size objects things go out of wack. The bed is perfectly aligned using a vernier, the extruder has been perfectly calibrated, all stepper motor steps are perfect. I have two main consistent problems across all parts:

Firstly, when I do solid fill at the beginning and end of my part it is not perfectly solid. (3 layers above and 3 below as default). When I tear the raft off at the end, the raft is more solid than the actual final outer layer. It looks like support structure on the outside.
Secondly, when my nozzle jumps from one object to another or bridge, it doesnt leave a string behind it as I retract my filament. However, it does leave a blob as it comes into contact with other side or pillar on each layer.

It appears that the filament is very sticky as it comes out of the nozzle. I have raised the temperature incrementally up to 250C to see the affects but just creates bad surface quality.

I have changed so much settings that not sure which ones are the good ones and which are the bad.

Anybody got some advise?

The first problem is easy to fix "lower your speed " bigger parts might required more top solid layers to end up smooth, specially if the infill under it's small. So to fix your problem number 1 increase number of top solid layers and reduce your speed. (You can try higher temps instead of lowering speed, but results won't be the same) .

Your second problem is related to temperature, your hotend is too hot and even when you have a good retraction setting, the filament inside it's melting too much an so when start extruding again the liquefied plastic creates the blobs. You mentioned 250 so I assume you are dealing with ABS, from my own experience don't go beyond 240, I never go beyond 230 for ABS and 215 for PLA. So to solve number 2, lower your temperature drastically.

Speed and temperature, the most important settings in 3d printing.

Edited 2 time(s). Last edit at 11/13/2014 08:08AM by ggherbaz.

Hi ggherbaz

Thanks for advice. I find the speed has a great impact on quality but I am not printing close to optimum speed here. Some say prusa can run print at about 100mm/s without problems yet I am printing at about a quarter of that which makes a 2 hour print take 8 hours. If I print at 50mm/s I start having consistency problems with the infill and support structures but not the perimeters which is a little weird. Maybe some vibration on bearings or something or maybe steppers cant handle it. I have some shiny nema 17 steppers so shouldnt be a problem. I now opted to grease all my bearings as well to try eliminate any shuddering. The printer is stable as a rock though and everything is nice a tight.
On the temperature side, I print mostly at about 230C. However, after reading up a lot it appears the temperature can be raised to improve adhesion which was also a problem when I raised the speed. I therefore tried a few prints with 235/240/245 and 250 and depending on size and complexity of part I saw some improvements but in others not. The lower temperature does help with the elimination of the blobs though thanks.

"If I print at 50mm/s I start having consistency problems with the infill and support structures but not the perimeters which is a little weird."

Perimeters are always set to be printed at lower speed by the slicer.

To try to print at those speeds, you need to:
1 use 3mm filament. (Can be done with 1.75, but your extruder needs to be perfectly tuned)
2 use 0.6 and up nozzle.
3 very high quality filament with a lower melting point.
3 small objects and very simple forms.

Thanks for the advice. Definitely need to look at increasing print speed.

Yeah, I'm in the search for that holy grail too. My last print was a painful 36 hours one.

I can print fast if I don't care for quality, the problem is that that's what my customers want.

Good luck on your quest.