Nozzle tip scraping last layer on transverse

[snowygrouch 1]

Hi,

I have recently found some problems with the printhead nozzle tip scraping across the

last printed layer. I thought initially I just had the table too high, but it often happens after the

first layer...but if it does it on the 20th layer then surely its not the initial bed height....

I use CURA at the moment, is this a common issue ? Can you make the head jump up (well ok the table

jump down) during moves to cure this?

I dont think I am extruding too much plastic as the prints look pretty much ok and dont have that

bulging look. Also I dont think anything mechanical is slipping because overall the prints look fine.

This is at 0,2mm layer height with PLA filament at 230 deg C head temp, 50mm/s printspeed, 150mm/s transverse.

Thoughts ?

Calum Douglas

[codemaven 0]

I'm not sure about Cura, but in NetFabb you can make the bed lower on jumps... However, it's more trouble than it's worth. The head does scrape across the top of your last printed layer, but I've never had it damage anything. It makes a noticeable path in the surface when it does, but this is usually on internal layers that you won't see in the end result. You might have some unavoidable jumps on the top surface with some models, but again I've never had any issues with this and have not found it to cause any serious cosmetic problems on the top.

Cheers,

Troy.

[phut 0]

I find this is the most extreme when your extrusion volume is excessive, normally due to filament and drive variations.

When your extrusion volume is correct then there's usually no scrape, but what does happen is that the nozzle wipes a bit of material into the print that causes a line in the print (particularly in the cases where you might be printing at higher temperatures).

I find the most problematic issue this causes is that the head pressure builds up if the overextrusion continues, because it means that the extruder drive has to slip to compensate. The actual scrape is usually not a problem though, normally the sprung bed takes up any movement that's necessary to let the nozzle pass.

You can try Slic3r too, that has the option to move the head up on travels. But beware that this is also followed by the head pressure drop and results in extra ooze (which in slic3r you can configure to have a retraction before this). Also in comparison to Cura, I find slic3r very aggressive on retracting, which has caused me many a problem with filament grinding previously when I ran the stock filament pinch thing (versus my current sprung pinch roller).