Nozzle size vs layer height?

Just finished getting my prusa up and running and trying to get some prints dialed in (using slic3r). I'm using 3mm filament (ABS) with a 0.35mm nozzle.
It looks like for thicker layer heights, the perimeters are not adhering to the previous layer correctly. By bringing the layer down to 0.2mm (keeping everything else the same) I've managed to get what I'd consider a good print. (see attached image) It seems to happen on layers with sparse infill (solid top and bottom layers look fine). I think my steps/mm is dialed in pretty good (did a number of tests).

My guess is that it is either
1. For thicker layer heights the extruder runs faster and occassionally strips. I've adjusted the idler tension and stepper current as high as I can and it doesn't seem to help.
2. Sparse layers are calculated differently? Do I need to force the extrusion width on the advanced tab?

In the attached image, the prints are (left to right) 0.2mm, 0.25mm, 0.30mm.

I'm able to get good prints at 0.3mm with the same nozzle (different extruder) on my cupcake (using skeinforge) so I know it's possible!

Edited 1 time(s). Last edit at 01/15/2012 11:53PM by tsb4k.

More Heat !




Michael

Edited 1 time(s). Last edit at 01/16/2012 08:56PM by Hardwarekiller.

Hardwarekiller Wrote:
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> More Heat !
>
>
>
>
> Michael

I tried bumping the temperature quite a bit and I'm still getting the same effect.
I should probably have posted this in the printing forum, I don't think it's a slic3r issue so much now.

I noticed that when it starts doing bridges the extruder can't keep up at first. The problem probably lies there (not with bridges but with the extruder)

Edited 1 time(s). Last edit at 01/16/2012 11:04PM by tsb4k.

If more heat does not help then slow down all extrusion speeds and try again.

Are you trying to bridge faster than the solid infill speed?

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[richrap.blogspot.com]

I had bridge speed at the same as solid infill.
Right now I have perimeters at 30mm/s and infill at 60mm/s. I'll try turning all the speeds down.

Slowing it down hasn't really helped.

I'm not being very systematic about this but my next hunch is the z-axis. Since the effect seems to go all the way around the affected layer (not just the beginning which I would expect if the filament was just lagging) I wonder if I have inconsistent layer height.

Now that I think about it, I didn't install the springs in the x-ends on the threaded rods..

Do you have z lift turned on? That is the only real way you could end up getting backlash in the z direction. Otherwise you are constantly moving in the same direction, so backlash would not rear it's ugly head.

tinyenormous Wrote:
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> Do you have z lift turned on? That is the only
> real way you could end up getting backlash in the
> z direction. Otherwise you are constantly moving
> in the same direction, so backlash would not rear
> it's ugly head.

I don't have lift enabled. I tried it once but had basically the same output.

Right now I'm trying to eliminate mechanical problems:
-Replaced printed idler pulleys with bearings + fender washers
-Tensioned all belts
-Re-leveled platform with the springs more tightly compressed

My next steps are:
-Test the extruder with another set of gears to make sure they aren't wonky (looking for periodic errors)
-Mount the heated bed pcb onto an aluminum or glass plate (I don't like the little bit of flex it has)

What heat are you running?
It looks like a heated bed, if so does you're power supply/s have enough power?

Gulf Wrote:
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> What heat are you running?
> It looks like a heated bed, if so does you're
> power supply/s have enough power?

I believe so, I haven't seen any abnormal behaviour or shutdowns.
I will measure the 12V line during a print to see if it is sagging at all.

While printing with the extruder and bed at operating temperature, the 12V line was always at least 12.1V.

If I extrude from pronterface it seems like I can see slight variations in the rotation speed of the extruder gears. Getting the idler tension and stepper driver current balanced has been a real problem for me.

Maybe I will try to swap over the geared stepper from my cupcake to see if this is the case.

For reference in case anyone searches this thread, I replaced the wade's with a makergear stepper extruder and the sparse layer problem has gone away. I still have poor layer alignment but at least I know that is mechanical. This whole thing has been unrelated to slic3r, except that it allowed me to get prints done much quicker for troubleshooting.