Bottom Layer Compression (over extrusion) - Can't get rid of it

Question

I've been trying to find a solution to a problem I've been having recently whereby the bottom layers of my print (1.2 mm; 12 layers) are either being compressed. over extruded or both. The problem results in the nozzle being dragged through previously extruded filament leaving deep groove marks and the bottom layers being risen/wavy, thus causing (I believe) the print layers to expand horizontally outwards

Settings are:

• Anycubic Chiron
• 0.1 mm layer height
• 200 °C hotends temperature
• 55 °C bed temperature
• 40 mm/s print speed
• eSun black 1.75 mm PLA
• Cura 4.4.1

It's less noticeable on less intrinsic prints but for my latest project, its becoming a real issue. The problem is that for the square holes for the buttons (of which there are a lot), the bottom layers are extruding (essentially elephants foot-ing) which is impacting the tolerances of the build (holes should be 13 mm to accept 12.5 mm square buttons but are coming out at ~12.7 mm only on the bottom layer, I've measured the walls of the square holes and they're coming out perfectly).

I've tried almost everything I can think of/find on Google:

1. Levelling the bed (multiple times)
2. Tried print temps from 190 °C to 210 °C (even printed a temp tower which confirmed printing at ~200 °C is correct for my filament (eSun black PLA)
3. Calibrated the extruder
4. Calibrated the Z-axis
5. Set different horizontal expansion settings in Cura
6. Reduced entire print flow rates (have tried 90 %, 85 % and 80 %); this somewhat worked but produced problems elsewhere in the print due to lack of material (skin overlap etc.)
7. Used the 'modify settings for overlap' mesh setting to reduce infill flow & inner wall flow to 45 % and 55 % respectively for the bottom layers (up to 1.2 mm).

The last point in that list is where I've had the most success but it does leave a slight indentation around the outer wall until the full flow rate kicks in (i.e. >1.2 mm) and I'm thinking there may be other things at play that are causing the issue and I shouldn't have to do this reduce bottom layer flow so much if at all.

Has anyone seen this before?

Answer 1

I had the same problem with bottom 8-10 layers being squashed. Tried all the possible settings and nothing helped.

Eventually found that the bottom part of the Z-axis guide rails was narrower then the top and it was not rolling properly down the bottom.

Found out by taking off the Z-axis rod and moved extruder up and down and I felt it was moving a lot worse/getting almost stuck down the bottom. Also tried it by disabling steppers and rolled the Z-axis motor by finger, almost no effort at the top to roll it down, but took a lot more effort down the bottom 5 cm or so.

I loosened the screws and pulled the bottom part wider and problem solved... Probably a rookie mistake as it is my first printer....

Hope it helps someone saving days of experimenting.

Answer 2

So I managed to figure it out and it turns out the vertical guide screws had a lot of grease/oil build up near the bottom which was impeding the X axis motor from properly moving the nozzle vertically when instructed.

After removing both guide rods and cleaning with degreasing fluid, the troublesome problem is no more!

Answer 3

The first thing that comes to mind is that, even though you have levelled the bed, the print nozzle may be too close causing too much "squish" on the first layer. Squish isn't bad as it promotes adhesion, but in your case, as you are looking for finer tolerances on the holes, it may be a problem. I use a feeler gauge and aim for 0.15 mm gap when printing at 0.2 mm layer height.

Next thing to consider is ensuring you have calibrated your flow rate/extrusion multiplier. See here for detailed procedure

Assuming flow rate is calibrated I can think of some settings in Cura that could affect your print.

• Initial Layer Flow
• Flow Rate Compensation Factor
• Combing Mode / Avoid Printed Parts

Initial Layer Flow enable the use of a higher/lower flow rate in you first layer. Typically I set this to a value larger that my flow rate, 120 %, as I want good adhesion and am less worried about the elephant's foot effect. However, you could reduce it to less than your flow rate although that may compromise adhesion unless you use a brim.

Flow Rate Compensation Factor For most circumstances this should be 100 % which indicates that your flow rate should be used as set and not compensated for. I would check that this value has not been altered cause over-extrusion.

Lastly, there are two travel settings. Combing Mode and Avoid Printed Parts work in combination to reducing the impact of travels in the finished print. I would ensure you have combing turned on (e.g. Not in Skin) and that you have enabled Avoid Printed Parts. More details on these settings can be found here

Answer 4

I had similar issues during the past few days. My first 3~5 layers overlapped. I ended up with figuring out it was the screws to mount Z stepper became loose and the stepper shifted itself downwards instead shifting up the nozzle for the first several layers, until the stepper had nowhere to go.

Answer 5

I have had a similar problem after years of clean printing and spent ages messing with it until I read this article and cleaned my lead screws on the Z-axis - a quick hit with a brush seems to have fixed it - fingers crossed.

Problem: my layers looked over extruded in random areas inside models and by the time I hit the top layer, I got some pretty serious results with blobs big enough to change the detail and fill in large gaps with ooze.

I tried the following:

• Tweaked my Cura settings for ages in case I had retraction set wrong, wiped back to factory defaults, regressed to earlier versions of Cura - no luck,
• Replaced my hot end assembly pretty much three times over, no luck except to clog a few brand new hot ends lol
• Used different filaments, dried filaments including new ones in the oven for a day, no luck. Probably wasted a couple of rolls of PLA persisting with trying to get a job completed through the problem.
• Cleaned the lead screw. It may have improved it somewhat but is difficult to tell as it is somewhat random.

UPDATE: The problem is not fixed, unfortunately. I will try a more detailed clean of the lead screws tomorrow, but I ran a 100 mm clean Z-axis raising test and noted it was pretty close to the mark, but interestingly it was about 99 mm on the left side and 101 mm on the right, although I doubt this could fully account for the problem I am having from about 2 mm up the axis unless the z height loss occurs in one concentrated section right near the bottom. The printer previously printed well and has not been damaged in any physical way that I am aware of. I will consider if there is any degradation in the functionality of the stepper motor by swapping them if more cleanup doesn't help. Keen for any other ideas if you have any.