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Small Layers Not Adhering

Posted by gtg252b 
Small Layers Not Adhering
July 10, 2012 01:13PM
I recently upgraded from a 0.5mm nozzle to a 0.35mm nozzle, and after some calibration I'm finally able to get decent prints again. One issue that I'm still having though is that small parts of the print aren't adhering to the previous layers. The two attached photos show the issue pretty well. Any ideas what I'm doing wrong?

open | download - Layer_Adhesion_1.jpg (298.1 KB)
open | download - Layer_Adhesion_2.jpg (412.9 KB)
Re: Small Layers Not Adhering
July 10, 2012 02:59PM
Most likely your layer height is too high. If the W/T ratio is much less than 1.5 it will not adhere.

Re: Small Layers Not Adhering
July 10, 2012 03:02PM
I've tried both 0.2 and 0.15. Do you think I should try thinner than that?
Re: Small Layers Not Adhering
July 10, 2012 03:51PM
Using Slic3r? I found setting the nozzle size to .3, ( [forums.reprap.org]) and a minimum layer time of 15 seconds (cooling tab) really helped my prints.

Thingiverse ID Alan1279
Re: Small Layers Not Adhering
July 10, 2012 05:39PM
0.25 or lower should work but the W/T must be 1.5 or more.

Re: Small Layers Not Adhering
July 11, 2012 08:40AM
Well, I tried a layer height of 0.1 (which should yield a W/T well over 1.5), and it's the worst one yet.

Dad911, I'm already using a minimum time higher than that (I'm at 25 seconds). Maybe I'm slowing the printer down too much... I'll try dropping that time down some.
open | download - IMAG0147.jpg (274.5 KB)
Re: Small Layers Not Adhering
July 11, 2012 10:11AM
Try a cooling fan when printing the smaller bits......

The bottom looks quite good, so the layer hight looks ok to me.
Are you printing each part completely before moving on to next part? (just looking at the difference between the parts)
If so, the extruded plastic may not get time to cool between layers, cooling fan should fix that.
You say you have a cooling time at 25sec, does the extruder suck the filament back up and what happens when it continues. Maybe there is not enough plastic extruded just after a pause?
Just my thoughts....

Re: Small Layers Not Adhering
July 11, 2012 12:39PM

I've got a cooling fan on there already (and a duct too). I should have mentioned this in the first post, but the 4 parts in that image were all printed independently. For each one I trued tweaking some settings to see if I couldn't fix the issue.

That 25 seconds is just the minimum layer time, so it slows down small layers to get to that time. I do have the extruder retracting before moves (to prevent stringing), but it doesn't seem to be causing a problem with restarts... maybe I should have it extrude a tiny bit extra on restart.
Re: Small Layers Not Adhering
July 11, 2012 01:44PM
If you think it's retract, I'd try printing the part with it turned off, that would at least let you know if it's the issue.

I had an issue where my extruder was missing steps on the retract, because the speed was too high, it was not at all obvious, the gear chain on the extruder combined with the speed of the operation makes it virtually impossible to here a missed step.
Re: Small Layers Not Adhering
July 17, 2012 03:06PM
I finally figured it out. After trying everything I could think of (different temperatures, different speeds, different extrusion parameters, etc), I finally decided to switch out the filament spool. the first print after putting a new spool on there came out perfectly, and now I've been getting excellent prints for several days. I guess the previous roll had just sat out too long and absorbed too much moisture from the air.

Attached is a before and after photo using the same Slic3r settings to print the same calibration piece (http://www.thingiverse.com/thing:24238).

Thanks for your input!
open | download - IMAG0163-1.jpg (265.4 KB)
Re: Small Layers Not Adhering
July 19, 2012 09:02AM
One more update for anyone who has similar issues to this. I've got access to a computer controlled oven at work, so I thought I'd try to dry out the spool that was causing me issues. I programmed the oven to run at 75C for 8 hours, and then drop and hold at 40C until I pulled out the spool, and I let it run over night. The hold at 40 was just to keep any more moisture from getting in there. After doing that, the print quality improved significantly. It's not quite as good as a new spool, but it's actually usable again.
Re: Small Layers Not Adhering
July 23, 2012 09:39PM
What type of climate do you live in? I have been wondering if my filament is absorbing too much moisture when it sits out. My spools usually sits out on top of my printer until the spool runs out which could be up to a few months. I live in southern California where there is very little humidity, but I still wonder if enough moisture is absorbed to mess up my prints. I haven't had any super poor prints though.
Re: Small Layers Not Adhering
July 23, 2012 09:44PM
I'm in Atlanta, GA. This time of year, it's VERY humid here. Today the humidity topped out around 90%.
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