latreides
Posts: 21
Joined: Sun Apr 16, 2017 12:47 pm

Gaps in the bottom layer?

Fri May 12, 2017 8:05 pm

I am having difficulty printing the bottom layer of some objects. Firstly the infill doesn't actually "fill" the entire area, and secondly it often creates very tiny stand-alone pieces that don't stick to the bed very well.

Here is an example of both of these in action:
Image

Here is the top layer, it prints exactly how I would expect the bottom layer to print:
Image

The main reason for the difference seems to be the First Layer Width. I have to set this to a much higher value to get adhesion.

Is there any way that I can keep the width larger but still get (mostly) the same result as the top? If I increase the Outline Overlap to some absurd value like 85% then I can get the gaps to fill in, but this causes more issues than it solves, and doesn't fix the issue with the small pieces.

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pixel3design
Posts: 22
Joined: Sun May 17, 2015 7:48 am
Location: Ravenna, Italy
Contact: Website

Re: Gaps in the bottom layer?

Sat May 13, 2017 4:40 am

As far as I can see, you have an extrusion % in first layer over 100.

I find it quite useless (IMHO). I better use 125% height for the first layer (eg. nozzle 0.4 -> layer 0.2 -> first layer 125% [first layer became 0.25]).
First layer won't be squashed down (useless for PLA/ABS/PVA/PET-G, useful only in PC and Nylon) and this means less postprocessing with blades, and at the same time S3D autoadjust flow to make extrusion consistent.

Results are:
  • same good adhesion
  • right infill (in your case)
  • hotend less prone to bed crash
Hope this helped.

Cheers
Io non credo in un Dio personale, non l'ho mai negato e anzi l'ho espresso chiaramente. Se c'è qualcosa in me che può essere definito religioso, quella è la sconfinata ammirazione per la struttura del mondo così come la scienza può rivelarcela.

E.Albert

latreides
Posts: 21
Joined: Sun Apr 16, 2017 12:47 pm

Re: Gaps in the bottom layer?

Sat May 13, 2017 12:38 pm

pixel3design wrote:As far as I can see, you have an extrusion % in first layer over 100.
I mentioned this, yes. I have the First Layer Width set to a much higher value to get adhesion.
pixel3design wrote:I find it quite useless (IMHO).
I cannot get a first layer to stick without increasing the width. Its most definitely not useless.
pixel3design wrote:I better use 125% height for the first layer
I can increase height to 200% and it still won't stick, but increasing the width makes it stick.

I have a leveled bed, with the nozzle height at the correct distance from the bed, using a heated bed covered with a BuildTak sheet, that has been cleaned with Isopropyl Alcohol, and I am extruding PLA. There is nothing more I can imagine doing to try and get the first layer to stick other than mess with the extrusion thickness and height does almost nothing for me, where as width makes it stick great. So I am trying to deal with the fallout of a larger width on the first layer.

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dkightley
Posts: 2313
Joined: Tue Mar 10, 2015 4:09 pm

Re: Gaps in the bottom layer?

Sat May 13, 2017 2:21 pm

Here's my thoughts....

Your part has a fairly thin section, so I would not use a first layer thickness over 100%. Using a value over 100% will result in fewer extrusions....meaning a greater possibility of gaps being generated by the slicer. Increasing the width moves the extrusions apart...and the amount extruded is increased to compensate for it.

You've not shown a picture of the actual print....so we can't see if there's any sign of the nozzle being too far away from the bed. My guess is that it is....which means you should adjust the Global Z offset by a negative amount to raise the bed. This will squash the first layer into the bed a bit more, giving greater adhesion. Adjust and print. If adjacent layers have not amalgamated and there's no sign of the "elephant foot" effect round the outside edge, then adjust it again.

Finally, you've made no mention of first layer speed. I set this speed at 50%. With a slower speed, the first layer is likely to be pushed better into the bed.
Doug Kightley
Volunteer at the National Tramway Museum http://www.tramway.co.uk
Railway modeller and webmaster at http://www.talkingtgauge.net

latreides
Posts: 21
Joined: Sun Apr 16, 2017 12:47 pm

Re: Gaps in the bottom layer?

Sun May 14, 2017 1:53 am

dkightley wrote:Your part has a fairly thin section, so I would not use a first layer thickness over 100%.
I know that reducing the first layer thickness to 100% allows the gaps to be filled, but this is not an option. It takes a fairly large first layer thickness for the part to stick to the bed.
dkightley wrote:You've not shown a picture of the actual print....so we can't see if there's any sign of the nozzle being too far away from the bed. My guess is that it is....
I want to be clear, I am not trying to troubleshoot bed adhesion. I spent the better part of two months doing this and got nowhere. I have adjusted the nozzle height hundreds of times trying to get it just right. Nothing has worked except adjusting the first layer extrusion width. I have no desire to revisit that nightmare.
dkightley wrote:Finally, you've made no mention of first layer speed. I set this speed at 50%. With a slower speed, the first layer is likely to be pushed better into the bed.
For that model my first layer speed is 30% of 10mm/s, but again, I am not trying to troubleshoot bed adhesion. I just want to know if its possible to get S3D to fill in those gaps when I have a large first layer extrusion width (without making the overlap more than 30% or so).

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pixel3design
Posts: 22
Joined: Sun May 17, 2015 7:48 am
Location: Ravenna, Italy
Contact: Website

Re: Gaps in the bottom layer?

Sat May 27, 2017 4:16 am

Well... So we got an underlying problem. I'm sure your bed is definitely leveled, but what about initial nozzle height? Even before print you have a gap between nozzle and bed, which will increase as first layer begin to be printed. Sum layer height and initial Gap and you get bad sticking part.
Try to decrease the first layer by 50um in the GCODE tab (eg. Z offset -0.05) and print just 3 or layers and send us the result.
BuildTak is a beast on retaining polymers on its surface. So something is wrong in your setup.
And as always, Cheers
Io non credo in un Dio personale, non l'ho mai negato e anzi l'ho espresso chiaramente. Se c'è qualcosa in me che può essere definito religioso, quella è la sconfinata ammirazione per la struttura del mondo così come la scienza può rivelarcela.

E.Albert

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