max retraction speed in Firmware

Discussion in 'Calibration, Help, and Troubleshooting' started by R Design, Jun 14, 2016.

  1. R Design

    R Design Well-Known Member

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    I was just trawling through some old posts by guru Richrap and I found this one:

    https://plus.google.com/+RichardHorne_RichRap3D/posts/M7KMXdvnXfV

    where, in one of the comments, he says:

    I'm now interested in why the extruder max speed is set slow (25mm/sec) I'm normally up at 32mm as a minimum, better if you can get to 38mm/sec for retractions.

    The first thing I realise is that "I'm an idiot" because all this time I've been naively playing with retraction speed in S3D wondering why it didn't make a difference!

    I checked on the LCD and max retraction speed is indeed set to 25mm/s (RC6).

    So I went through configuration.h and configuration_adv.h but couldn't find the relevant parameter? Anyone know where to find it in the firmware? Anyone changed it yet?
     
  2. R Design

    R Design Well-Known Member

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    Finally I found it - on the 4th attempt!

    #define DEFAULT_MAX_FEEDRATE {150, 150, 6, 25} // (mm/sec)

    It's the last number - for the extruder.

    So, did anyone change it yet? How high did you go?
     
  3. Alex9779

    Alex9779 Moderator
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    Hmmm interesting, I didn't look at this... If you take into account that Greg set the retraction rate to 70mm/s in his ram purge script this seems pretty useless if the firmware is limited to 25mm/s
     
  4. Alex9779

    Alex9779 Moderator
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    I think I am going to play with these, the UM2 has 300mm/s for X and Y, the head is much much lighter so 150mm/s is ok for the BB.
    Z is 40mm/s and E is 45mm/s...
    Maybe I just set Z to 25 and see how it goes on some test travels... And e to 100 (?) and test how the motors behave at that speed...
     
  5. R Design

    R Design Well-Known Member

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    I had XY at 150 in S3d for a while to help with ooze problems (less time for it to develop during moves) but found that print quality was reduced quite a bit (a lot of variation in the layer lines). Now using 100mm/s. For me that is the biggest reason to lighten up the print head (I think the rods are way to lightweight for the printhead & allow it to twist all over the place.... am currently considering going full Bowden with the spool mounted just over the middle of the bed to have a really short PTFE!)

    Reading Richrap, if you can get 100 for E then that is amazing! Who knows with Titan....

    40 for Z is a lot more than the 6 that Richrap set and even more than the 3mm/s that was the original on the Kickstart BB. I wonder....
     
    #5 R Design, Jun 14, 2016
    Last edited: Jun 14, 2016
  6. mike01hu

    mike01hu Well-Known Member

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    Hmm, I don't see the twist in mine after finding that most clamp screws had worked loose or, more than likely, settled in. Also, there are no real stresses to cause the issue as all cables and filament feeds are suitably free. The only thing that can possibly cause twist is poor alignment of the Y axis.
     
  7. R Design

    R Design Well-Known Member

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    Interesting. You're right the idler and the Y-motor carriage screws come loose really easily.

    On mine if I push the X carriage in the Y direction from above or below the bars it twists - in a rotation around the X axis - quite easily.

    After weeks of examination I've become convinced that this is the principal reason why print quality deteriorates at speed. Of course I could be completely wrong but I've also noticed that lots of printers do use much thicker rods and sturdier structures, even when they are smaller.

    If my BB is different to yours the only thing I can think of (everything is tight) are those "crashes" into the back wall I had in my first week before I learnt how to work with the quirks of RC3.
     
  8. mike01hu

    mike01hu Well-Known Member

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    It's not the first time I had run into the trouble but I have now been brutal, against my better judgement, in tightening the screws with an Allen key rather than the hex screwdriver.
     
  9. R Design

    R Design Well-Known Member

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    I'm so much happier now I've upped the max retraction speed to 40mm/s in firmware....

    Way snappier!
     
    Stian Indal Haugseth likes this.
  10. Alex9779

    Alex9779 Moderator
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    Ok I tried up to 150mm/s for the extruder motor but it starts skipping steps when decelerating at the end of a move at about 145mm/s.
    I set my max to 125mm/s now...

    @Spoon Unit when you experimented with the Volcano and the ram purge did you increase the default value?

    And I tried 25mm/s on the Z axis which still works nicely. I move the bed to the bottom and to the top and the distance between the bed and the nozzle seems still to be the same...
     
  11. R Design

    R Design Well-Known Member

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    My understanding is that one of the things that can happen with a high retraction speed is that the molten filament "breaks" and so the retraction doesn't happen effectively. However I haven't found anyone writing about this in detail. I guess the only way is to increase the retraction speed slowly and then discover when the results stop improving / start getting worse. That's why I just put in the 40mm/s Richrap referred to since yesterday I just wanted to print and not do experiments. Apparently some molten plastics "break" more easily during retraction....

    Yes, I was thinking about @Spoon Unit too!

    On the Z-axis, apart from the convenience a higher speed offers when manoeuvring, Richrap was talking about it in the context of retractions, lifts and XY movement during a print. I think his point was that, if the bed drops away quickly then that will combine with the retraction to create a clean "cut" at the end of a track.
     
  12. Alex9779

    Alex9779 Moderator
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    Basically I was looking for a faster travel... I think I will not go past 6mm/s during a print. And the retraction z hop is so small, I use 0.25mm, I don't think you reach very high speeds anyways...
     
  13. Alex9779

    Alex9779 Moderator
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    But I just found some strange issues with the Z, doing homing at 10mm/s gives me squeeking from the Z axis, doing the same speed as a move command it is not?! Gotta investigate a bit further...
     
  14. Spoon Unit

    Spoon Unit Well-Known Member

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    I only fiddled with the tool change script. I never went into Marlin to see if more speed could be allocated there. Using only the tool change script, I found there was a limit somewhere in the region of 1250 to 1350. Beyond that, any higher value resulted in the same speed.
     

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