Beautiful Start - Bad Toplayer Finish

[firatdede 0]

Hi Friends,

We started using Ultimaker 2. I wanted to print this thing.

http://www.thingiverse.com/thing:412346

And Up top layer didn't printed as good quality unfortunately. It has lots of gaps.

 

I read something about backlash. But I don't thnk this is problem. Because first layers and inner layers were perfect. Only toplayers have gap problem like that.

 

How can I fix? :/

 

Thanks

 

[dreamworker 1]

Can you share your CURA settings, in order to understand where is the problem?

 

[Nicolinux 288]

This looks a bit like my issue with strands of filament not touching. Check out this thread:

 

• http://umforum.ultimaker.com/index.php?/topic/5375-top-layers-not-touching-um2/
  

 

[Dim3nsioneer 558]

You may check in the expert settings of Cura if you have both solid top and bottom infill activated. Do you use any plugins for this print?

 

[firatdede 0]

No I didn't used any plugin.

My Cura Settings:

Layer Height: 0,2mm

Shell Thickness: 0,6mm

Print Speed: 80mm

Fill Density: %45

Bottom & Top Thickness: 2mm

Yes in expert setting solid infill and bottom fill is ok. Also It makes initial layers fully closed. But up layers like that.

We bought our machine 1 week ago and using. So machine is new, I don't think about mechanical problem :/

And one photo more:

 

Same problem. :unsure:

 

[gr5 2,224]

It looks like underextrusion. It could be backlash/play but I don't think so.

The strange thing is the shell passes look perfect - not underextruded.

So I'm thinking your infill speed must be faster than your shell speed. This is adjustable in Cura - I recommend infill speed is 0 which makes it the same speed as shell.

Having said that, you need to be careful about how much the printer can extrude. 80mm/sec at .2mm with a .4mm nozzle - multiply those 3 numbers together and you get 6.4mm^3/sec. That is pushing the limits of the UM2 if you are printing at 230C. If you are printing colder than 230C then you are beyond what most UM's can do (maybe you have extra low temp PLA - every color is different). Here is a graph (dark blue line) showing max speeds for .2mm layers for a given temp. Try to stay at half the speed of the blue line for your temperature:

http://umforum.ultimaker.com/index.php?/topic/4127-um2-extrusion-rates-revisited/

So either slow it down or raise the temp (check the graph!).

 

[firatdede 0]

@Nicolinux : yes nearly same problem :/

I changed temrature to 230 degree. And Slowed down to %50 speed (40-50mm/s or less)

 

This is the image from printing. At bottom thing is looks good first layers. But other two thing is finished objects with lots of gaps. They're inner fill is normal. But Up finishing is like that. Side shells have no problem. I think backlash can affect this too?

 

[gr5 2,224]

Please take a picture much closer. Try a cell phone as cell phone can get very close.

It *could* be backlash. But then I would expect the shell passes to have gaps in spots. Also I would expect the infill to have two-lines then gap. Then two-lines, then gap. I don't see that but maybe I need better photo.

Are all 3 parts in the image above at 50mm/sec and slower?

 

[Nicolinux 288]

I think gr5 is also right. If you look on the vertical side walls, you'll see that entire layers are missing or receding inwards. This is a sign for underextrusion.

My problem is that all lines/strands except for the first layer do not properly touch eachother so the surface is not "watertight". But your's looks like it is leaving out the outer shell completely.

 

[3dmaker4u 0]

What if actually the code generated by Cura is wrong?

 

[illuminarti 18]

A 0.6mm shell setting in Cura is going to cause the printer to print the entire print using a 0.6mm extrusion width (because the shell thickness isn't an exact multiple of the nozzle width, so it compensates by pretending the nozzle width is 0.6mm).

So the volume per second in the original example is 80 x 0.2 x 0.6 = 9.6mm³/s. Which is probably too high for a decent, sustained print.

Also, you're only going to get a single pass of the extruder around the perimeter, which is more likely to lead to poor quality being visible due to oozing during combing moves, and/or infill showing through.

I'd set the shell thickness to 0.8mm, and so get two 0.4mm passes, and 0.4mm thickness throughout the print. Also, do you really want ten layers of solid material on the tops and bottoms, but much less on the sides?

 

[gr5 2,224]

GOOD CATCH! I didn't notice the .6mm shell. So that's the whole problem. The infill is also trying to extrude .6mm wide lines with a .4mm nozzle. Which you can do if you slow it the hell down. Change shell to .6mm and change the speed to half the speed on the graph I pointed out to you.

This is an easy one to fix now that I see about the .6mm shell!

 

[kolia 31]

You mean the "shell thickness" parameter in Cura is actually used not only for the wall/shell, but also for infill??

 

[gr5 2,224]

yes. But in a complex way. If shell is .8 and nozzle is .4 then infill is .4. If wall is .5 and nozzle is .4 then infill is .5mm.

Cura will print from I believe 75% to 150% of nozzle width so if nozzle is .4 then from .3mm to .6mm. If shell is .3 then you get one .3mm pass and infill is .3mm. If shell is .7mm then you get two .35mm passes and infill is .35mm.

So try to always set shell to integral multiple of nozzle width!

edit: fixed some numbers.