CURA 3.4.1 Profile definition problem? (SOLVED)

[RoboDLC 0]

I have both CURA and Simplify3D and go back and forth between them depending upon my projects.  I recently completed a new delta machine of my own design and have run into a problem.

My Simplify3D profile works just fine, but I tried to create a profile in CURA that mimics these settings and it is a miserable failure.  This is the first time I have had absolute failure in this process, but it is also the first time that I have tried to mimic profiles between the two programs too.  I have attached a picture of the two results, the left is S3D, the right is my customized CURA 3.4.1 profile. 

This problem is obvious.  But not the cause...

Clearly I am under-extruding in CURA, filament grinding makes me think that I am under temperature as well, but I am not.  It could be CURA is trying to push filament too fast, but why?  Both programs are set to the same speeds (so far as I can tell) and same temperatures.  I am missing some nuance.

Is my "micromanagement" of the CURA settings the cause of this?  I don't use the CURA stock settings ever since I typically use delta printers, and eSun PLA, for instance, likes 225C, not 200C (stock CURA PLA settings).  What settings have I obviously run afoul of?

 

Many thanks all.

Edited August 30, 2018 by RoboDLC
further elucidation

[nallath 674]

Did you also set it to use the same acceleration & jerk? The speed is actually setting the max speed, which is quite different from actual speed (which is the result of max speed, acceleration and jerk)

[RoboDLC 0]

1 hour ago, nallath said:

Did you also set it to use the same acceleration & jerk? The speed is actually setting the max speed, which is quite different from actual speed (which is the result of max speed, acceleration and jerk)

Nope.  I wouldn't know what to set it to.  S3D does not expose any acceleration or jerk modifications that it may put into the gcode.  I assume that it is using the firmware defaults.  I do not set those values at all in my CURA profiles.

[nallath 674]

So my guess is that those are probably what's causing the issue.

[tinkergnome 691]

18 hours ago, RoboDLC said:

Both programs are set to the same speeds (so far as I can tell) and same temperatures.  I am missing some nuance.

 

...and both are set to the same filament diameter? (i'm just guessing)

 

[RoboDLC 0]

Update:

No idea about acceleration and jerk.  It is nothing that I have ever fiddled with in CURA before and I'll need to read up on just what it does.

Yes, the filament is 1.75mm in both S3D and CURA settings.

HOWEVER

I found something that is starting me on the way to a fix.  This printer has a VERY effective part fan ducting system.  I dropped the starting fan speed in CURA to 40%, with a maximum of 60%.  This eliminated the filament starvation, but I still had some rough spots in the beginning.  I then SLOWED the first layer down to about 6mm/s and this cleared up the initial roughness at the plate.

The attached print is of the beloved "Benchy" calibration print.  We start out well, end out well and go whack in the middle.  So, that is a puzzle.  I am running an S3D Benchy on this printer to see if the problem may be mechanical (one of the linear rails has a rattle to it that I don't like).

 

Thanks all for the suggestions,

DLC

[Nicolinux 285]

If you have the equiplent then just record the print so you can correlate head movements with the temperature graph later. To me it looks like a temporary problem since the top prints well again.

[RoboDLC 0]

The solution appears to be obvious now.
As I noted above, when I turned down the part fan, I got better media flow and it stopped under-extruding.  But I am getting a rough spot in the middle of the print.  I just did a Simplify3D print of the same part, filament, settings and speeds as CURA (as much as I can match these).  That print was also messed up in the exact same place.
SO...
It looks like the fan is my issue in CURA.  It also looks like I have a mechanical stutter in my linear rails, or something else in the drive train of my delta.  I don't think that the issue lies with my "Itty Bitty Belted" extruder since the problem occurs at a specific time in the print that is clearly based upon height.  Maybe something is binding up, or a "flat spot" in my GT2 belts or pulleys.  I will do a complete tear-down and check all those parts.  I have had issues with these rails before - It may be time to get another set if I can't clean them out to fix them (or whichever one it is).

Thanks for your help everyone,
DLC