First few layers of my 3D prints are shrinking

[ferjusdado 0]

Hello everyone,
I have a 3D printer that seems to be having some issues with the first few layers of my prints.
Specifically, I am noticing that the layers after the very first one are shrinking in size compared to the rest of the print.
This issue seems to resolve itself after around the tenth layer, but it is making it difficult to get good prints overall.

 

Hello everyone, I have a does anyone have any advice on what could be causing this issue and how I can fix it?

Any help would be greatly appreciated. Thank you in advance!

[gr5 2,027]

Some people only notice that it goes *outwards* at the bottom but you noticed the symptom more correctly than most.  The quick answer is "lower bed temp" or "change filament brand" but...

 

Why it happens:  PLA (it happens with some other plastics as well) when molten sticks to itself strongly - like snot or mucus.  Like a liquid rubber band.  It also cools quite a bit in the first few milliseconds while still liquid which makes it shrink.  So as the printer is laying down a trace and going around the corner it gets pulled inwards while still liquid.  Like a liquid rubber band.  On the bottom most layer it is held nicely in place by the bed.  But as you go upwards, if the already "solid" filament is still above it's softening temp (it should be!  See below) then the solid layers are like a soft clay and get pulled inwards slightly.  Eventually you get far enough from the heated bed (1/3 of the way up the indent) and the printer starts to recover and by the 10th or so layer is recovered.

 

Solutions:

 

Lower bed temp.  60C is recommended for PLA.  Some people do 70C and that makes the problem worse.  PLA softens right about 52C and it's important to keep the bed well above that temp!  If you don't then the corners will likely warp up off the bed and the part can even come loose and that can be a disaster - even destroying the print head if you have an S3 or S5.  You could try 58C.  It doesn't soujnd like a big difference but there is a world of difference between 52C and 60C so going to 58C is lowering it by 25% which is significant.

 

Filament.  If you manually extrude some filament and it stays in a thin line - similar width as the nozzle width then that's a good filament.  Some brands of PLA thicken just below the nozzle.  I'm not certain but I suspect the liquid rubber band effect is especially strong in these brands and you can get that "elephants foot" much worse.

 

CAD - you can model the reverse shape in CAD.  In fact the only part of this that bothers me is the very bottom which can be sharp.  So I sit "initial horizontal expansion" typically to -0.3 (yes you can do negative values).  This makes the bottom of my prints much better.

 

You might say - that's crazy - I shouldn't have to make my shape "wrong" in cad to make it come out right when printed!  Well that's what they do for injection molding - the people who create the molds (often low paid engineers in asia) do all kinds of tricks like this (e.g. no corner is 90 degrees such that when it comes out of the mold it then *is* 90 degrees).

 

[3dmodeling101 0]

 

Hey there! I also had a similar issue with my 3D printer when I first started out. From my experience, this issue could be caused by a few different things.

One possible cause could be that your bed isn't leveled properly, causing the nozzle to be too close or too far away from the bed in certain areas. Another possible cause could be that your filament isn't extruding consistently, which could be caused by a clogged nozzle or a problem with your extruder.

To fix this issue, I would recommend starting with leveling your bed and making sure that it is completely flat. You could also try adjusting your nozzle height to make sure that it is the correct distance away from the bed.

If that doesn't work, you may want to try cleaning your nozzle or checking your extruder for any clogs or issues.

Hope this helps and good luck with your prints!

[JTMD 17]

Can confirm build plate temp is critical.    pics below are identical parts printed in eSun PLA+ with identical setting except left one had build plate temp of 75C, right had 58C