Speed not affecting time.

[manisland 0]

I'm printing a project, and want it to print fast.

I have experimented with a lot of variables.

 

But SPEED has me befuddled.

I set PRINT SPEED to 100, along with WALL SPEED (inner and outer), and TOP/BOTTOM SPEED, TRAVEL SPEED.

I have all the INITIAL speeds set to 25.

All mm/s of course.

Slice.

Time = 58 minutes.

 

Change everything that was 100mm/s to 150mm/s.

Slice.

Time = 57 minutes.

 

In the analysis it says retractions is 40%, and skin is 23%, walls are 28%.

 

There is something I do not understand. If I am printing 50% faster (for most of the at least 51% of the time, I would thing I would see 25% improvement.

 

What do I not know?

Thanks.

 

[manisland 0]

Two more things.

First I have an Ender 3 Max Neo, which I've read should do either 150mm/s, or 120 depending on whom you  believe.

Second, if/when I change all the speeds down to 50mm/s (except initial settings) I get 57 minutes, same as 100mm/s.

Thanks!

[GregValiant 1,415]

Load the model, set Cura up to slice, use the "File | Save Project" command and post the 3mf file here.  Without having an idea of the model geometry it's hard to tell what's really going on.

 

These sorts of discrepancies are often associated with the Accel (and Jerk) numbers.  Depending on the length of a move, the printer may never get near 100mm/sec.  In addition, small features (towers, poles, etc.) can cause Cura to bounce off the "Minimum Layer Time" and Cura will slow the print speed down so a layer has time to cool before more plastic goes on top.

 

At the Ender 3's default acceleration of 500mm/sec² it takes 10mm to get to 100mm/sec and then another 10mm to decel back to 0.  So any move that is under 20mm can't hit 100 because it has to start slowing down before it gets to the 10mm point.  Consider also that the 20mm movement is "0 to 100 to 0" for an average speed of 50mm/sec.

 

Within the printer there are Maximum's for Accel and Speed.  It's possible to ask Cura to set Accel to 6000mm/sec² and it will go into the gcode that way.  Then the line gets to the printer and the printer says "No way...Max Accel is 500" and so the Cura time estimate is way off compared to how long the print actually takes to finish.

 

My older Ender 3 Pro will print large flat areas at 175mm/sec (over that the extruder can't keep up).  For small intricate models I might as well set it to 25mm/sec because it just can't get up to speed.  Enders aren't good at high Accel as the stops and starts are so violent that the machine can hurt itself.

 

So there are limiting factors that go well beyond the settings in any slicer.  If you are printing a large square box then you could print it at 100mm/sec and the printer would actually spend time at 100mm/sec.  A 10mm x 10mm box you can forget about high speeds as the printer just can't do it.

Now consider those who hang a big direct drive extruder and a gigantic triple fan duct on the print carriage.  They might need to drop the accel to 150 to keep from jumping teeth on the belt because of all the weight.

 

Finally, your printer is a bed slinger.  If the Y accel is too high and your print is tall and top heavy then it can throw the print right off the bed.  That has been known to happen.

[manisland 0]

I believe you are correct about acceleration.

The part in question is small, and has many structures, and nothing straight for more than a centimeter at most, except the bottom layers, which are thin.

 

The other test subjects I worked on/with were similar.

 

I put in my big project, which takes 12.5 hours and did trials  there.

It's a cover for a raymarine PFD, so picture a lid 13" by 8", and a lip 1/2". It's a big box cover.

all 5mm thick.

 

At 100mm/s the time projected was 12.5 hours.

At 150mm/s it was 11.5

and at 50mm/s it was 16.2  hours.

The small(ish) improvement for 100 vs. 150 is because it has a lot of short fill segments in the 5mm direction (thickness).

The largish improvement for 50 vs 100 is because the walls start to add in heavily.

 

 

You were a massive help in getting me to understand that concept.

I won't waste more of your time posting .3mf files.

 

Thank you so much!

I very much appreciate the help.

[GregValiant 1,415]

In the Infill section is "Infill Layer Thickness".  Try setting that to 2X layer height.  Then go to the Speed section and change the "Flow Equalization Ratio" to 0%.

The infill will go down every other layer, and with no flow equalization the printer will maintain speed in spite of the double layer thickness flow of the infill.

[manisland 0]

And thank you also!!

 

The 100mm/s case went from 12.5 hours down to 10hrs. That is a huge improvement.

I'll run some real/physical prints tomorrow on my test/benchmark case and see what results I get.

 

 

I am confused how this works on several points.

First on say layer 5, it puts down a double thick line for some fill. Does the software understand that on layer 6 there is already some PLA there, so it doesn't print then? That way printing every other?

(i.e. I don't have to worry about do I?)

Also:

If I am on, say, layer 5, and I put down a .6mm fill line, and the rest is putting down .3mm, when the tip is passing by some of .6 stuff does it bash into it?

Or is the fill always put down after the walls? I guess in my preview studies I see walls first, but my experience is limited...

 

I appreciate your time and effort! Thank you so much.

[GregValiant 1,415]

The important layer is the last layer of infill that the roof sits on.  Since that layer has always been correct for me I'm guessing that Cura counts down from there and the infill only goes down every other layer so the layer below is empty.  That's where the extra material goes.

Layer 11 - everything and last bottom skin

Layer 12 - everything but infill

Layer 13 - everything but with infill at 2X material

layer 14 - everything but infill

layer 15 - everything but with infill at 2X material

layer 16 - everything and first top skin.

So the top surface of a layer is where it is.  The extra material of the infill drops down to fill the missing layer of infill below.

The same trick works with "Support Infill Thickness" for all those inner support walls.

If the heavy flow of the double layers of infill/support lines bothers your extruder and it starts skipping steps then you can increase the "Flow Equalization Ratio" to slow the print head down.  That will take some of the pressure off the extruder so it can keep up.