UM2 nozzle

[shiremog 0]

Looking at the drawing of the UM2 nozzle, I notice a step at the bottom of the angle ( on the inside of the nozzle) where the 0.4mm hole comes through. Is there a reason for this or is it just the way it's made?

 

[IRobertI 516]

I believe it is there to help minimize oozing.

 

[shiremog 0]

I ask 'cause I'm getting carry-over of a previous filament, causing coloured streaks. Some of it is from the outside of the nozzle where I haven't cleaned it properly :roll: , some I believe is stringing in the bowden tube, but I suspect that some is trapped in that ridge inside the nozzle.

 

[IRobertI 516]

The easiest way to get rid of any residual plastic in the nozzle is with a so called "Atomic" or "Cold pull". You can read about how to do it here: http://support.3dverkstan.se/article/10-the

I do one of those every time I change filament. But with one difference. I don't remove the bowden tube at the head. Instead I simply pull the filament from the back of the machine. I'm using a different feeder design that allows me to release the filament to make this easier but it can be done with the original feeder as well, just make sure the stepper isn't powered on by turning the machine off when it has reached the correct temperature.

 

[shiremog 0]

Thanks for the tip. It appears that I'm on the right track then. What material is the bowden tube? Looks like standard 6mm nylon pneumatic tubing.

 

[Nicolinux 288]

One (maybe) interesting bit about the atomic method. Apart from the fact that some people seem to have had better results with Taulman 618 (pull temperature 140°), one should not rely completly on it. I just had the case where several subsequential pulls were clean and then "the last pull" showed dark spots around that shoulder on the tip. This seems to be the case when switching from Colorfabb XT to PLA.

 

[shiremog 0]

So it does appear to be a design feature. I was thinking about making a replacement without the step, which I reckon would reduce the carry-over & reduce the chance of a blockage, but perhaps it would cause another set of problems. Has anyone tried it?

 

[gr5 2,070]

I'm certain ultimaker employees have tried it. Or reprap designers. But I don't know.

 

[shiremog 0]

If I'm feeling bored one day, I'll make one & try it :ugeek: