Nozzle Size, Feed rate, Flow Rate question

Hi,

I have one of those kickstarter MK8 clone extruders, with a .350mm nozzle. It's the only extruder I have so I don't have anything else to compare it to. After running through the calibration shapes in the wiki, I feel I am close to having a well calibrationed extruder. I am using ramps 1.4 with Marlin, and Skeinforge 50. I am printing 1.75mm PLA from ultimachine.com.

The problem I am having in that for small shapes the extruder performs well. But with larger prints the extruder jams. The extruder motor starts to stall and the extruded filament starts to thin out. If I pause the print and loosen the set screw I can't push the filament through the extruder by hand or with pliers. It is also difficult to pull the filament out of the extruder.

What I have been doing is pulling the filament out, cuting off the end and then pushing it back through. When I do that a glob of plastic comes out the end of the nozzle, (about the size of a pea). When I do that I can continue the print fine. Except I have a pea size glob of plastic somewhere in my print. The extruder jams up at a fairly regular intervals.

I believe the problem is that plastic builds up in the hotend until it starts backing up the filament tube, and clogging it. So I am trying to figure out which of my setting is off?

1. Flow rate? I have it set at 30 (note this is for SF50 so it is based on the filament going into the extruder). If my flow rate is too high then plastic can't get out of the nozzle quick enough. But I can't believe that 30mm/s is to fast for this extruder. I know other people run it faster.

2. Feed rate? I have it set at 30mm/s. I matched the feed rate to the flow rate with the calibration shapes. If the feed rate is to slow the calibration shapes should be oversized but they arn't.

3. Temperature? I ran it at 185C 190C 200C up to 230C. It doesn't seem to make much of a difference.

4. Edge width over height? I have this set at 1.8. Haven't changed this.

5. Layer Height? I set this to .3mm, after the calibration shapes.

6. Filament size? I measured this, it runs about 1.73 - 1.75 mm.

7. Filament density? I set this to 1.0.

Anyone have this problem? Any suggestions?

Which setting in SF50 sets the width of the extruded plastic filament? I think with the settings I have I am trying to lay out too thick of a path. I think I need to make more passes with less plastic per path.

Thanks,

Seems like easy stuff you will figure out. Sounds like your Z=0 may be too close. Try starting .1-.2mm higher that you are now. That would cause a jam to develop over a few perimeters.

Otherwise your larger perims are printing faster AND you are getting jamming because the nozzle motor can't keep up with the force to drive cold filament into the heated nozzle. Suggestions include a tighter hobbed bolt/gearhead setting.

It could also be fighting the filament roll - make sure it rotates EASILY.

Colder is always prefered because structures will bridge or widen better without warping. Also less or no dribble (oozing) from the nozzle at lower temps. I started higher, it is not good.

Simba,

Thank you for the suggestions. I have tried a number of different starting heights, and I have printed with and without a raft. Doesn't seem to make a difference.

The set screw for the filament against the hobbed bolt is a challenge. I have played with it a lot. It could be the problem but I don't think so, because when it jams it is jamed in the hotend, and there isn't a obvious problem at the cold end. I can't push the filament through the hotend even with pliers, until I pull it out frist.

I have had problems with the filament feed in the past, but I still have this problem when the feed is completely slack.

I have one of these Kickstarter extruders too although I'm not printing with it yet. However, based on my other printing experiences I have a couple of suggestions you could try.

Temperature - you said you started at 185C and went up. Did you try going lower?
My Huxley will happily print some colours of PLA at 170C.
You need just enough heat going into the nozzle to melt the filament as it is pushed through by the extruder. The faster you extrude the more heat you need. Slower extrusion needs less heat. If you raise the temperature too high the heat will spread up the steel tube and melt the filament too high up in the extruder which can cause a jam.

Layer height - you said you had set layer height at 0.3 mm and your width over thickness ratio to 1.8, i.e. 0.54 mm. So you are trying to fill an oval with 0.3 and 0.54 mm as the maximum and minimum diameters with plastic coming through a nozzle diameter of only 0.35 mm.
Reducing the layer height to 0.25 or 0.2 might make for better extrusions.

Finally, I routinely print through a 0.3 mm nozzle and find that printing fast seldom works. Try lowering the speed as well as the temperature and see if you can print without any jamming. Once you've got that nailed you can gradually increase various settings.

Good luck and I'll be interested to know how you get on.

richgain,

That is a very good point... At 0.3mm layer height and weight over height at 1.8, the crossectional area that the slicer is expecting is .127mm^2 (pi*r1*r2). But the area of my nozzle is actually supplying is only .096mm^2 (pi*r^2).

Since I calibrated the flow rate in the firmware to fill the 20mm box shape, I am extruding much more plastic that I should be for that feed rate. My extuded plastic filament is running at 30% faster that my feedrate, in terms of linear movement.

I should start with a layer height and width over height to something that matches the nozzle. So at 0.25 layer height the w/h should be like ~1.98. Or ~.26 layer for 1.8 w/h. And then adjust from there.

I think I will updated these values and redo all of the calibration shapes.

Thanks again for the suggestions. I will update the thread with my results.

with a 0.35 nozzle and the speeds you can extrude, i would do layering at about 0.15mm hieght. anything more will cause your extruder to slip from back pressure.