Can't get rid of this line / gap in circular prints

[astrodenny 0]

I'm stumped on why I'm getting these gaps or lines in my prints, mostly when the print involving circular drawing. Here are two pics

The first print is a recreation of "Fat Man"; the first atomic bomb

As the extruder head rotates around the print, the filament seems to "jump" in the same section.

Here's another print of a funnel. It was a failed print, but you'll notice the same gap/line located in roughly the same cooridinates. In both cases the line appears and seems to occur in all circular prints.

 

After printing the atomic bomb, I noticed my X-Y motors were a bit loose. I tightened these up, then printed with retraction on. Here is the reprint of the atom bomb

 

The line is still there. There are also some inconsistent layers, but I beleive this is due to a much needed axis alignment. It's the line/gap that is driving me nuts.

In a previous post, I'm also having issues with my Z axis - but not sure if this is related.

http://umforum.ultimaker.com/index.php?/topic/2294-z-axis-drive-nut-assembly-loose/

Any help is greatly appreciated.

 

[owen 19]

It looks like the Z seam, which happens on the Z move. It seems less in latest Cura and is adjustable in KISSlicer.

 

[astrodenny 0]

Hi Owen - thanks ... I've noticed this seam also on some (very rare) square prints. Does it also have an effect on cornering? For example a cube's corners seem a bit bent and not sharp?

 

[gr5 2,266]

It's a z seam. It's either where the head turns around to do the inner wall (if you have one) or more likely it's where the head pauses while the z axis moves up to the next layer.

What's probably happening is there's still some pressure in the head and a little plastic oozes while the print head isn't moving.

Maybe you can reduce pressure by printing more slowly or at higher temperature. Or alternatively maybe lower temperature will reduce leakage? I would try it on a small cylinder. Experiment with speed and temperature. Take notes. And pictures. Let us know what happens. The nice thing about a tall cylinder is you can change settings while you print. Both cura and the UC let you change print speed and temperature while printing so you can print a few mm, mark the cylinder with a sharpie and then try a new settings. Keeping notes as you go.

[astrodenny 0]

Thanks gr5 - I'll give this a shot and report back!

 

[astrodenny 0]

gr5 - One other question - one of these prints were done using the quickprint settings in Cura. So, if the quickprint settings are preconfigured, shouldn't the z seam be less noticeable or non existent?

 

[gr5 2,266]

Most people don't care about the z seam. I don't know what the "quickprint" settings are and I don't really care but I will just take a guess and say it prints at a higher mm/sec which I would expect to emphasize the z seam as extruder is going from "fast" to "stopped" and you will get a little leakage.

There are several obvious limitations of the UM. One being you can't print in mid air. A less obvious one is that when the feeder slows down or stops, the plastic keeps oozing for a little while and the opposite: when you speed back up it takes a little time for the plastic to be back up to speed. This causes all kinds of minor imperfections and there are tricks to reduce these. One is to print with less volume of plastic (slower). One is to print hotter. One is to reduce speed changes: speed up your z axis - read about it in the forums - so it doesn't stay in one spot as long or slow down head movement so a brief stop is less contrast from full speed.

Another z seam trick is to place it at a different spot on each layer. Kisslicer does this. You might want to try it once you've mastered every setting in Cura. Another trick is the joris setting but this only works for cups and can completely mess up slicing for something that isn't a cup.