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Fixed dual extruders make a mess


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Posted · Fixed dual extruders make a mess

Hello. I have been using Cura for over 3 years now but for the first time I now have a dual extruder system. What a disaster...

1. When other extruder is waiting to heat to printing temperature both heads are hovering over the print oozing on it and melting it

2. If I set "Standby temperature" = "Printing temperature" there is still some delay while both heads are sitting still over the print melting it but more importantly after 2-3 layers my printer halts with "Heater error" message.

 

I have carefully reviewed all Cura setting having anything to do with dual head printing but failed to find one allowing to move heads away from the model while heating.

Neither was I able to find out why keeping both heads at printing T results in error.

 

Any ideas?

 

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    Posted · Fixed dual extruders make a mess
    14 hours ago, zet said:

    I have carefully reviewed all Cura setting having anything to do with dual head printing but failed to find one allowing to move heads away from the model while heating.

     

    If the firmware of the printer does not handle this, there are extruder (start/end) scripts in Cura that are intended to be used for these "extra stuff" that shall happen on every tool change.

    Is it a custom printer or do you use one of the pre-defined multi-extruder configurations in Cura?

    Extruder scripts can be created and edited in Cura machine settings (AFAIK).

     

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    Posted · Fixed dual extruders make a mess

    It's a custom coreXY machine, Hypercube style

     

    You mean "Extruder Start/End G-code" ? I wonder how to do this efficiently enough. If I add some code to move extruders away from the model while heating between tool change, it will make printing time quite a bit longer.

     

    Ideally I'd like inactive extruder to reach printing T right in time, while the other head is printing.

    It seems like Cura is actually trying something of that sort but very poorly. While printing I see some strange target T for inactive head, not defined anywhere in settings. For example standby T 200, printing T 240, octoprint shows target 215.

    But the result is always the same, extruder will stop about 5mm over the model for anywhere between 5 to 30 second, oozing and melting everything.

     

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    Posted · Fixed dual extruders make a mess
    11 hours ago, zet said:

    Ideally I'd like inactive extruder to reach printing T right in time, while the other head is printing.

    It seems like Cura is actually trying something of that sort

     

    Yes, actually that's the key feature of Cura for multi-extruder prints. It works great, but....:

    For a custom machine you have to find the correct values for the following settings first (by experiment):

    • "Heat Up Speed"
    • "Cool Down Speed"
    • "Minimal Time Standby Temperature"
    • "Initial Printing Temperature"
    • "Final Printing Temperature"
    • "Extrusion Cool Down Speed Modifier"

    That's what Ultimaker provides for their own printers with the "quality" profiles for each supported material.

     

    The inactive nozzle will probably always ooze a bit while (re-)heating (depending on the used hardware of course). I would try to fight it with longer tool change retractions and proper primetower/ooze shield settings.

     

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    Posted · Fixed dual extruders make a mess
    Quote
    • "Heat Up Speed"
    • "Cool Down Speed"
    • "Minimal Time Standby Temperature"
    • "Initial Printing Temperature"
    • "Final Printing Temperature"
    • "Extrusion Cool Down Speed Modifier"

    Thanks you. I am currently on Cura 4.7.1 

    I wasn't able to find Heat up and Cool down speed settings. Will try and play with the others.

     

    On a separate note, can you please explain what is meant by "bridge wall" and "bridge skin" ?

    And if there a setting allowing to make sure bridges are printed across the shortest distance? I have attached a model I am trying to slice, you'll see what I mean.

     

    dual fan duct.stl

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    Posted · Fixed dual extruders make a mess
    3 hours ago, zet said:

    And if there a setting allowing to make sure bridges are printed across the shortest distance?

     

    I have no clue...

    I may be wrong but I don't think it's possible to control this with a setting.

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    Posted · Fixed dual extruders make a mess

    Yet another question

    In my case 2 nozzles are 25mm apart and both can reach every point of the bed.

    If I specify Nozzle 1 offset as 0 and nozzle 2 at -25mm Cura shows 25mm of left side for 1 and 25mm on the right for 2 as unreachable.

    What is nozzle offset supposed to be relative to ?

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    Posted · Fixed dual extruders make a mess

    I am also unable to find "Heat Up Speed" or "Cool Down Speed" anywhere in Cura. I was able to set all four material temps (Print, Initial, Final, and Standby) the same with no errors and it did fix my delays, but I wanted to start printing PLA as support for PETG without it gumming up the nozzle. I ended up with a workaround in Marlin that is working for me.

     

    First, I autotuned my PID settings following this guide, which helps them get up to temp and stabilize faster. Next, since I was still experiencing delays, I changed TEMP_RESIDENCY_TIME to 0 seconds in Marlin (the default is 10). This makes it not wait for temps to stabilize - it starts going as soon as it's within TEMP_WINDOW (which defaults to 1°C).

     

    I still experience a short delay every 5-10 extruder changes, so I plan to increase the TEMP_WINDOW to 5°C or so. The delay is caused by the temp overshooting and Marlin waiting for it to get back to the window from the other side. I figure since Cura doesn't see any problem starting and ending extrusion 10°-15°C under temp, a measly 5°C of overshoot isn't worth waiting around for.

     

    Its not like temps are stable after waiting anyway, since Cura starts at the Initial temp but immediately sets the Print temp, which causes a 5°C overshoot (on my printer at least) 20-30 seconds into the layer. This means even if we could tune "Heat Up Speed" and "Cool Down Speed" and everything were working as it should, there'd still be a 20°C range where Cura is allowed to extrude plastic: 5° from the overshoot after going from Initial to Print, and 15° (by default) from Print to Final, plus maybe even more overshoot the other way if it doesn't finish printing in time.

     

    As for nozzle offset, I have mine configured in Marlin under HOTEND_OFFSET_X (and Y or Z). All hotend offsets should be relative to the first one, just as you have it. By configuring it in Marlin, they're in the same spot from Cura's perspective. When I execute a T0 or T1, the carriage automatically moves to position the new extruder where the old one was.

     

    Last thing - if you want to change where it pauses to wait for temps, I'm pretty sure it always does it over the prime tower when it's enabled.

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