under extrusion in low res prints

[kevin-osborn 9]

I read the topic about spool tension, but this seems different.

My prints come out fine (beautiful even!) when I print with .1 layer height,

but when I print .25, they come out full of holes and extremely weak.

At first I thought something happened between the time I printed the first one of these parts, and the second at lower res, but today, I printed a smaller test (next set of pics) back to back. The .1 print was fine (and took place after the crappy part in the first pic) and the .25 print was bad.

https://lh4.googleusercontent.com/-hEGNXSweHRM/Uv4y1-qv6pI/AAAAAAAApIg/-qK20SrlOBo/w769-h460-no/14+-+2

https://lh4.googleusercontent.com/-xRU0ueZNtbk/Uv4y13oXcoI/AAAAAAAApIQ/hv1S3fULp8Q/w769-h460-no/14+-+1

all the other parameters (except Layer height) were the same

shell thickness .8

bottom/top thickness .6

fill density 10%

print speed 50

Cura version 14.01

Firmware version 14.01.2

Jan 10 2014 13:20:34

 

[Dim3nsioneer 558]

Have you already tried to increase the hot-end temperature a bit? It will make life easier for your printer to melt 2.5 times as much plastics as for the 0.1mm layer height print.

You may also want to have a closer look at the extruder while it is printing the .25mm-layers. Make sure the motor doesn't skip steps and the knurled bolt doesn't slip while transporting the filament.

 

[woofy 12]

Hi Kevin,

Your printing too fast and your extruder cannot keep up.

Your printing at 5mm³/Sec and many of our UM2 machines top out at less than that.

Try printing finer/slower/hotter until you find the optimum.

This thread should interest you:

http://umforum.ultimaker.com/index.php?/topic/3976-almost-always-missing-layers-underextruding/

 

[kevin-osborn 9]

I read that thread. Really 50mm/sec is too fast? My printrbot plus can do better, and Ultimaker advertises "A well tuned Ultimaker can reach 150mm/sec."

I'm not sure if there is confusion here, both prints are done at 50mm/sec, and the .1mm resolution prints are the good ones.

Isn't the point of lower res, to print faster? less layers at least. and if I have to slow down a lot to print lower res, it will take a lot of that advantage away. Just trying to understand...

As to temp, I'm printing ultimaker pla at 225. I'm not sure when it will start burning, but it seems like I'm getting into abs territory here!

 

[woofy 12]

Its not just the speed, its how fast the plastic can be squeezed out of the nozzle.

At 0.1mm layer you are extruding 0.1*0.4*50 or 2mm³/Sec

At 0.25mm layer you are extruding 0.25*0.4*50 or 5mm³/Sec

That is 2.5 times as much plastic every second.

You could try printing Illuminarti's extrusion test and see how your machine performs. I think the link is around page 8 or 9 in the thread mentioned above.

 

[kevin-osborn 9]

Ah thanks WoofysPlace! that makes sense now! It's all tradeoffs isn't it!

I think that is the missing piece (well probably not the last) in my understanding.

And to be truthful, I didn't read the whole thread! I have my homework cut out for me!

 

[gr5 2,267]

240C is a safe temp. You will not burn the PLA. You will be able to print much faster at 240C than at 220C.

The biggest disadvantage of 240C is that you are more likely to get stringing.

 

[shurik 87]

While my experiense is somewhat limited yet, I have had my fair share of the similar problems.

All the advices above are correct.

For the simpler solution, you may try to increase the flow to 150% or so while printing on 0.25, rest of the parameters unchanged.

 

[kevin-osborn 9]

ok, tried illuminati's extrusion test. Failed miserably. started seriously underextruding at 5mm3/sec and then eventually missed enough to miss some layers.

This is at 230C. Trying again at 240. Any suggestions?

http://umforum.ultimaker.com/index.php?/gallery/image/3587-extrusion-test/

(BTW, can someone tell me how to post images? when I use the icon for images it says I'm not allowed to use that in this community)

btw here is the link to the test:

http://umforum.ultimaker.com/index.php?/topic/3976-almost-always-missing-layers-underextruding/page-8&do=findComment&comment=33427

UDPATE:

Better at 240C but still failing, briefly at 7mm3/sec, and then badly at 9mm3/sec

I was unspooling by hand to make sure there was no tension.

http://umforum.ultimaker.com/index.php?/gallery/image/3588-240c-back/

http://umforum.ultimaker.com/index.php?/gallery/image/3589-240c-front/