Optimal Cura settings for large objects?

[lcocea 5]

My interest in this topic is related to printing large objects that I intend to use around the house. I chose an Ender 3 Max (advertised to do 300 x 300 x 320 mm) and Cura.

 

After some trial and error I managed to print my first large project: a flat (~390 x 290 x 5 mm) divider for my freezer drawers, made of 2 overlapping parts designed in Blender and assembled together with snap-fit joints. I successfully printed out 2 copies and then I ran into a "not sticking to bed" problem that required a reevaluation of most adhesion parameters previously used.

 

Here is what works for me right now (brass nozzle 0.4 mm; PLA filament 1.75 mm; bed cleaned with 70% isopropyl alcohol, not 99%):

 

- Layer height: 0.2 mm

- Initial layer height: 0.2 mm

- Top/Bottom thickness: 0.8 mm

 

- Printing temperature: 200 °C

- Printing temperature initial layer: 210 °C

- Build plate temperature: 60 °C

- Build plate temperature initial layer: 70 °C

- Print speed: 40 mm/s

- Initial layer speed: 5 mm/s

- Enable print cooling = False

- Build plate adhesion = True

- Build plate adhesion type = Brim (8 mm)

- Z Offset = -0.05 mm [using 'Z Offset Setting' plugin by fieldOfView]

- Enable draft shield =  True [Experimental setting]

- Draft shield X/Y distance = 10 mm

 

Setting the offset to -0.05 mm after bed leveling is important as it seems to enhance bed adhesion. Enabling the draft shield is a condition to avoid warping; not sure whether it works by preventing drafts or by providing additional mechanical stability to the printout but I find this feature particularly useful in my case.

 

The parameters above give me a nice-looking printout. The problem is that it takes 25 h to print one part and 21 h the other. This is still acceptable for now as I only need 4 copies for this project. Soon I will start a new project, where I need to print 6 different parts of a ~900 x 600 x 250 mm object. I feel that, with the inevitable trial and error required for optimization, my next project may take months to complete.

 

Any suggestions?

 

Edited September 12, 2022 by lcocea
Added clarity to title

[GregValiant 1,330]

I have the glass build plate on my Ender 3P.  I haven't had any trouble with adhesion with PLA.  For PETG I always use AquaNet Super Hold hairspray.

You know your printer best so these are just some thoughts rather than suggestions.  I'm just looking at the picture and these would be my settings for PLA.  I did move to an all metal hot end when the stock one died.

• Skirt instead of brim because that part has so much surface area on the plate I'm confident it wouldn't lift on me.
• Infill density 10% and Infill Layer Thickness 2X the Layer Height so it only does the infill every other layer.
• Combing off because no one is really going to see that piece and combing moves can add a lot of time.
• 50° bed 205° hot end as those are my norms.  I print Silky PLA hotter as it has poor layer adhesion.
• Print speed at least 75 and maybe even 100 for the skins.  That includes the first layer and I set "number of slower layers" to 0.  Small parts I might print at 30 to 35.  For a big piece like that I just want it done.
• Accel 500 and Jerk 8.  Those are the defaults.  You have a heavy Y system and too much accel on the Y is a bad thing on a bed slinger.
• I wouldn't bother with the draft shield unless the printer location is actually subject to drafts.  I have an air conditioner vent above my printer so I printed a deflector for it.  PLA isn't very prone to warpage so as long as there isn't a cool stream of air blowing at the printer it should be fine.
• When printing PLA I always run my initial layers at 105% flow.  I want that squish in case I missed the leveling by a bit (I'm a paper leveler).  I can't remember the last time I had a bad first layer.  I wipe the build plate down with alcohol between prints.
• I start with the layer cooling blower at 0 and at layer 6 it's at 100%.

With those numbers and a print speed of 75 - a 220 x 220 x 5 rectangular solid comes out to an 8:32 print.

There is a trick you can play with Accel.  If you put M201 X1000 Y500 in your start up gcode then you set the Accel in Cura to 1000mm/sec².  That M201 line would limit the Y to 500 and so X moves would be quicker at 1000 but Y only or XY combination moves would be at 500.  The printer can live with that.

When you have simple shapes like that you can export them from CAD at a lower resolution.  Lower resolutions result in longer line segments in the toolpath and they are more efficient (at the cost of not looking as "smooth" in the print).  You could also turn up the "Maximum Resolution" in the Cura Mesh Fixes section.

Finally (I've been waiting to change colors on my current print) a print speed of 5mm/sec at .2 layer height and .4 line width works out to 0.4mm³/sec flow rate through the nozzle.  That's just too low.  If you are having layer adhesion problems slowing down below 25 isn't going to help.

 

[lcocea 5]

To follow up on this, the Ender 3 Max fan is a beast. To avoid warping, I need to turn the fan on at a height of 10 mm or greater (layer 51 in my case). I get good glass bed adherence only if first layer temperature is at least 70 ⁰C. I realize this may be PLA brand-dependent as well so I have to experiment more.

 

Edited September 16, 2022 by lcocea

[GregValiant 1,330]

That could be a filament brand or water content problem.  Some mouse ears might help.  There is a Tab anti-warping plugin in the MarketPlace that you can try out.  Bring them in and slide them around to provide more bed adhesion at the corners.  You would trim them off later.

I designed the mouse ears into this PETG part as I knew it would want to lift.  You can see how hard it was pulling and this was with hairspray as well.

 

You have a big bed.  If you were to add a G4 S300 line to your StartUp Gcode right after the M190 bed heating line it would give the bed an extra 5 minutes to equalize across the surface.  (The G4 "S" parameter is in seconds).

When my glass bed was new it wasn't as consistent as it is now.  You might want to try a glue stick or hairspray to aid adhesion and keep those corners down.

Edited September 16, 2022 by GregValiant