Cura ignores flat pockets < 0,15mm

[dxp 23]

Hi,

sometimes, large and flat parts are very hard to remove from the bed. So I used large pockets with a depth of 0,15mm to reduce the adhesion area. But with that distance, the extruded plastic curls. You cannot lower the depth of the pocket, because Cura ignores everything smaller than 0,15mm - you will see it in Cura preview. Green is bed contact area, blue is pocket (and a print into air).

So how to make Cura accept flat pockets? Files with 0,05 and 0,15mm are attached.

Adapter HY20_00.stl Adapter HY20_05.stl

[P3D 46]

Hi, I loaded both files and sliced them, there doesn't seem to be any difference - is it the same file, perhaps?

[dxp 23]

Thank you for joining in!

The files have to be turned upside down, the picture shows the bottom view. Left you will see the circle rendered, on the right side it is ignored (pocket depth 0.05mm) and not printed.

But yes, the're almost the same.

[P3D 46]

I'm so sorry, my fault - I accidentally loaded the same file twice. Now I see it. 

 

I could reproduce the behaviour, but I also arrived at the results you wanted (at least in the Cura preview). 

 

What you want to do (part of the surface just 0.05mm above the build plate) is only possible with an initial layer height of 0.05mm, otherwise it will be either

-rounded up to the layer height (possibly making the plastic curl) - that is the case if your initial layer height is 0.05<=0.1mm (or, more generally, more than the depth of your pocket, but less or equal to twice the depth)

-ignored (making your object stick firmly to the build plate) - that is the case if your initial layer height is >0.1mm (or, more generally, over twice the depth of your pocket)

 

So to sum it up: Just set initial layer height to 0.05mm, then it should work - but only if your printer can reliably print such thin layers. Otherwise, it won't be possible, because everything in a layer has to be on the same z height by definition.

[dxp 23]

Oh, my initial layer heigt is 0.27mm, so 0.15 is rounded up and 0,12 is ignored. Now I understand. Thank you!

[geert_2 557]

What about changing your bonding method, so your prints can be removed easily?

 

For PLA, I use the "salt method": wiping the glass with a tissue moistened with salt water, prior to printing. No glue. This gives good bonding while hot, but absolutely no bonding when the glass is cold. So, models can be taken off very easily. But this is only for PLA, and for low flat models (not for "lantern poles"). For my old manual, see here:

https://www.uantwerpen.be/nl/personeel/geert-keteleer/manuals/

User neotko uses hairspray for bonding, and he removes his models by adding a few drops of window cleaner (if I remember well) when ready. This creeps under the models and dislodges them easily. This seems to work very well for his big models too.

 

For wood glue, some people put the model and glass bed in the fridge, and then it pops off.

 

Probably there will be other methods that are worth trying?

 

 

With the salt method, I can easily print these models at 100% infill, without edges lifting, and without damaging them when taking off after completion.

 

[dxp 23]

Thanks @geert_2,

 

your salt-method is genius, i tried it some weeks ago with success. But here it's about ABS.

• With wood glue and PLA i destroyed a glass plate in the fridge without any force (mixed it 1:3 - big mistake!)
• with aprinta pro the prints were ok, but i had to re-apply the glue after nearly every print
• the adhesion sheets were too sticky, the got worn out by removing after five prints
• on time i used bare glass and Isopropanol - worked
• the best results were produced using MagicGoo and z-offset: popping off after cooling down, no re-apply neccessary

Since removing flat parts was sometimes quite tricky, i developed the idea of removing  adhesive areas inside. To be honest, i found this technique on some printed parts by triangle labs for my Ender-3 Direct Drive Extruder and was eager to find a similar, aesthetically pleasing solution for me.

 

Right now I'm printing and it looks promising.