which rules? config.g vs slicer?

[fcwilt]

@opentoideas said in which rules? config.g vs slicer?:

To be fair I cant fault the Duet. It continues to exceed my expectations at every turn and the more I learn, the more impressed I am with its capabilities and its design.

One of the things I like most about the Duet family is that you can change any setting from the DWC console if you want to try something or verify something.

No more having to recompile the firmware to make such a change.

Great stuff.

Enjoy.

Frederick

[opentoideas]

@phaedrux
LOL I think sanity is unlikely or I probably wouldn't have gotten into this 3D printing lark but thank you for the kind offer.

config.g

this seems to be a reasonably stable starting point.

the machine is a CR-10 but with dual Z axis also a Titan Aero with volcano which I have rapidly realised is too heavy for the CR-10 carriage to support and a Precision Piezo Z probe which inst much help as between the carriage and flexible bed on this machine i get too much variation for it to be reliable.

like you said this "hobby" ticks all the right boxes and the engineer in me is already looking at ways to help resolve these issues but for the moment its meaning careful manual leveling and tweaking before each print.

@fcwilt I couldn't agree more. my biggest problem is the Duet is making it painfully obvious where the machine is lacking as there is nowhere to hide.

while the piezo always "worked" with the original controller and I was blaming myself for its misuse as soon as I got the Duet up and running it became obvious there was something strange going on and the more I checked the various mechanical parts the more apparent the problem became.

while in some ways ignorance was bliss at the same time now at least I can work to tighten things up and solve some of the issues.

[opentoideas]

oh dear, some of my confusion has now resolved itself into a reason even if I have no idea why...

@Phaedrux I hope you can help me with a puzzling problem with Cura, I have been printing test cubes this morning:

1 : acceleration, jerk and retraction disabled in the slicer - config ruling the print settings

2 : same as 1 but with retraction enabled in the slicer

3 : same as 2 with acceleration and jerk enabled acceleration 100 , jerk 1 (vs 300 and 5 in config)

while there was little difference between 1 and 2 I expected 3 to be the best of the lot but within a few minutes I knew something was wrong as after the first 2 slow layers it went to hell and started looking worse. and all my instincts pointed to acceleration being far to fast......

so I had a look at the Gcode files for them and cube 3 is strange in that where I expected to see speed and acceleration commands what I am seeing is M566 with settings of 1600 which I understand is jerk!

I am guessing that I have something fundamentally wrong with my Cura setup but I am at loss as to what. the only real change I have made since moving to Duet was in the machine setting and I changed the Gcode flavor from Marlin to RepRap as I was getting a ton of errors relating to a command that did not exist in Duet and this cured that problem.

I am totally lost with this though and off to see if I can find anything that may explain where I am going wrong??

turned off jerk control in cura which removed the strange jerk command so hopefully its not as bad as I first thought.. will have to come back to that later and see why I was getting those huge jerk numbers despite the low setting but for now onward and upward LOL

[wilriker]

@opentoideas First of all you need to check the units here. Jerk is given in mm/min (as opposed to mm/s). So a value of 1600mm/min means 26.67mm/s.

Then I think that jerk value of 5 (or 1) mm/min is close to having jerk disabled. The default if you do not set anything in RepRapFirmware for X and Y is 15mm/s or 900mm/min.

I just checked your config.g and apart from the very low jerk settings (again, I think you missed that this needs to be given in mm/min) at least I did not find anything obviously problematic.

Personally, I would never use any slicer's jerk or acceleration control. If I need to adjust the values I will do this via DWC at print time and if I like the settings I can immediately enter them in my config.g there as well.

[opentoideas]

@wilriker

thank you I had noticed the difference in units but you are of course right that i have such low values it is effectively no jerk. I think the main issue is I am trying to work around mechanical slop with settings while I wait on the parts to try and resolve the flex issues.

The problem is that the tool carriage just is not solid enough and corners are not sharp.

to my thinking (which is most likely wrong!) this seems to be under extruded on the straight sections but over extruded where there is a direction change and I have tried with jerk between 1 and 60 with no change so I think something else must be the issue.

speed is 20mm/s acceleration 100mm/s2 both of which I believe are quite slow. all of which was to try and combat the sloppy head (its semi stable each time I tweak it but if I tighten it up enough not to move, the bottom wheel bracket which is unsupported will bend over time and I have to straighten it and start again. (was not designed for the heavy direct drive extruder but I am stuck with it for the moment)

I have some parts on the way to hopefully resolve the flex and I think until these arrive I may have to live with this.

[wilriker]

@opentoideas Your accel and jerk values definitely are very low. I had mine also set very defensively with only 400mm/s² acceleration when printing but just recently upped this to 3000mm/s² (this reminds me that I wanted to create an online version of an existing spreadsheet that will give you the acceleration your motor can handle...). Also my jerk value is set to 10mm/s or 600mm/min for X and Y.

In the image you posted I cannot see any under-extrusion (but I am not an expert on this topic) but there is at least some over-extrusion or the nozzle being too low so the filament has to squish out to the sides.

The not so sharp corners on the other hand might even come from jerk being a bit too low so it cannot take the corner fast enough to counteract on the remaining pressure in the nozzle. What you could try is to either activate Coasting in your slicer or tune Pressure Advance in RRF. I would at least say try the first (they both fulfill similar tasks by different means but enabling Coasting in the slicer is just a one-click-action).

[opentoideas]

@wilriker thanks again,

I think I will raise the settings back more to the default for the printer and have another try as I am reading that too slow can cause just as many problems as too fast.

I have had a play with pressure advance though not coast but from my limited understanding I believe these only change the start and end of an extrusion not during and these lines are one continuous run so I don't think there should be a difference but I could well be wrong.

[Phaedrux]

@wilriker said in which rules? config.g vs slicer?:

Personally, I would never use any slicer's jerk or acceleration control. If I need to adjust the values I will do this via DWC at print time and if I like the settings I can immediately enter them in my config.g there as well.

Well there are good reasons to let the slicer handle it. Mainly because it can set different values based on move type. Inner Perimeter versys outer perimeter versus infill versus solid infill versus first layer, travel, etc. The firmware can only set acceleration based on print or travel. So you have much finer grained control in the slicer which lets you optimize speeds for quality where it's visible and while still helping to eek out shorter print times. It also lets you use modifier meshes to modify settings for separate sections of the model. Go fast on the large wide solid base, and slow down for the detailed slender model on top of the base. One size fits all only works well when the model is rather homogeneous in its structure.

I treat the config as the default sane values and absolute max values. The slicer gets to determine the exact values during printing based on the rule set I've given it for that model.

@opentoideas That part looks a little over extruded. Have you calibrated your esteps value and extrusion multiplier? That should really be the first step.

Good sane starting values for print speed is 50mm/s, 600mm/min (10mm/s) jerk, and 1200mm/min (20mm/s) acceleration. Travel speed 200mm/s with 900mm/min jerk and 3000mm/min acceleration.

Too slow jerk can lead to the print head slowing down too much on sharp corners leading to plastic oozing out and making the corner bulge. It can also lead to jerky motion on otherwise smooth arcs. Same can be said for too slow acceleration.

Perhaps this is a good analogy. Have you ever used a silicone caulking gun? As you pull the trigger it pressurizes the tube of caulk and it starts to squirt out the tip. If you keep a steady pressure and distance from the work surface the caulking will look nice and even. If you slow down and speed up or pause your movement the caulking will still come out, even if you release the trigger due to the built up pressure. So the goal is to try and keep the print head moving in a fairly consistent manner throughout the print.

The firmware has something called pressure advance that tries to combat this by basically relieving the built up pressure sooner and more gently so that by the end of the move the pressure is at 0. This would be the next step to tune.

[opentoideas]

@phaedrux
jerk is one thats not seeming intuitive as I felt lowering it would reduce jerky sudden speed changes but what you are explaining matches what I was seeing with a sweeping curve being almost like low res step x then y then x etc. rather than a smooth sweep.

I bumped things up but looking at those numbers I think I need to go further as there was a noticable improvement but not there yet.

I was initially hesitant to mess with the jerk numbers not fully understanding the implications and now wish I had listened to my own advice and left it alone!

Oh well, its not the first time and I am sure it wont be the last time I make things worse messing with something I dont understand.

Yet another learning experience!

While I get the description of pressure advance does it only change the start and end of an extrusion or does it also vary mid run like these corners?

I had thought the former but I realise that while thats the easiest way to describe the function the latter would possibly be more usefull and make sense too.

Whats the saying... a little knowledge is a dangerous thing.

Its easy to read the description of a function and assume you understand it but I get the feeling that while the description may be simple the implications are anything but!

Yes the extrusion esteps are callibrated but the extrusion multiplier.... best I could work out for this was its a fudge factor to adjust despite the calibration, which I figured would be an experience thing rather than something that could be calculated so I was leaving this for the moment as I thought it would be near enough until I ran out of other gremlins - wrong again?

[Phaedrux]

Messing with it can be the best way to learn. That's why I like to live tune things while a print is happening. That way I can quickly switch between two values and watch it for a few layers to see how it affects things.

Same thing with the speed and extrusion factor adjustments to live tune speed and extrusion multiplier. Adjust the multiplier until things are looking right, then just multiply your sliced speed or extrusion multiplier by the tuned multiplier and you get a new value to put into the slicer that should give you what you want.

You can kind of think of jerk as a minimum speed value. The system will try and maintain that speed through direction changes and will accelerate and decelerate before and after those speeds. It can get very technical beyond that basic description. Junction deviate and curve profiles, etc. That's getting into the weeds a bit for our purposes.

[Phaedrux]

0_1536790117534_50mm rounded.stl

You can use this STL to further tune your extrusion multiplier in Slic3r, or flow multiplier as Cura calls it. Print it in vase mode with no top, no bottom, and 1 perimeter. It'll take a couple minutes. If you have a 0.4 nozzle slice it at 0.2 layer height and 0.4 extrusion width. It should print a single walled square cylinder. Measure the thickness of the walls with calipers.

Old extrusion multiplier * (Expected thickness/Measured thickness) = New extrusion multiplier

Beyond that, you can make finer adjustments with the extrusion multiplier in the DWC or Panel Due until your perimeters have no gaps between them, and your solid infill layers are nice and smooth with no gaps, and don't pile up into ridges.

[SupraGuy]

@opentoideas said in which rules? config.g vs slicer?:

The problem is that the tool carriage just is not solid enough and corners are not sharp.

Just jumping in here, but this doesn't loik like a problem with the tool carriage, this looks to me like "ringing" where the belts are allowing the print head to continue moving on intertia for a moment after the motors have told it to print a corner. Shortly after the change in direction, the nozzle gets dragged back to its center position, but the result is a ridge off of the edge of the corner. As you print higher, these appear as waves on flat surfaces immediately after a corner, typically on the left side of the flat surface.

Tightening belts can help with this, as well as making sure that there's little compliance in the belt holders where it moves the carriage or printer bed. Also, reducing moving mass will help reduce the inertial pulling the print nozzle past its target. If these things are not under control, no amount of reducing acceleration values will make it stop.

[Phaedrux]

@supraguy I think he actually has a damaged print carriage mount due to a previous head crash.

But totally agree about belts.

From the photo it's hard to see what vertical print surfaces look like. Also the high number of perimeters could be causing some over extrusion. Caused by the way that plastic gets dragged around corners and get pulled inward.

Start with 2 perimeters and increase from there. Usually no more than 5 for when you want a really durable mechanical part. Plus it's usually faster to just add more top or bottom solid layers, since the print speed can be consistently higher, due to not having to make constant direction changes like perimeters do.

[opentoideas]

@supraguy

I have been all through the mechanics of this machine while I am waiting for bits to improve things and belts are tight and everything is as solid as can be expected with the exception of the bed which as its only held badly in the center and has a flimsy mounting plate that has compliance that gets worse the further from the centre you move. the X carriage was also never designed to handle the additional weight of the direct drive extruder and the bottom wheel mount not only flexes but bends out of shape over time.

to be fair the standard head with bowden is so light that this would not have been an issue so I don't blame the machine but until I get the parts to try and correct this its what I have to work with.

whilst I can tighten things up by the end of a print (or sooner) the weight has deformed the tang that the wheel bolts to and I have to disassemble it straighten it out and start again. this is obviously less than ideal and wont work for long as the tang will fatigue but hopefully long enough to print the parts I will need for the alterations.

yes there is clear ringing on the X and Y faces, on the bottom gaps from under extrusion and other artifacts on all sides. I think Phaedrux is on the right track and I messed up the speeds.

@Phaedrux

since I am gaining quite a collection here are all of the faces

I think the bottom face cube its the last one I printed with more normal settings and I will give your numbers a try next. now you mention it I think I upped the perimeters to 4 to see if that would help which it didn't so I will set that back to 2

I am looking forward to playing with the settings more once I have the mechanical problems sorted out but while the machine is so loose I am conscious that it will be difficult to know which settings are making real differences and what is just the result of poor mechanics.(especially for a novice like me)

My plan is to go for "good enough" and design / find the parts I need and print them. once I complete the repairs and get the machine a bit more dialled in I can then reprint the parts if I am not happy with them.