Printing limits



  • Hey all,

    I've been reading and thinking a lot trying to find bottom line of what is the thing that limits printing speed.

    I know all about mass, inertia and so on but for example what causes layer swift on high jerk, acceleration and speed? What makes the motor not capable keeping up and finally getting the swift? Is it something that you can overcome by nipping the current? Is it the cpu or the stepper driver overheating or a bottleneck somewhere?

    Hypercube currently running on 1500 acceleration, 20 jerk and printing on 110mm/sec getting some layer swift but not always.

    Open to all suggestions, more likely a brainstorm so I could break my printers limits. I'm thinking cooling with a peltier for duet, passive cooling maybe with fan for each motor or anything else that may help.

    Cheers!



  • If you’re using sane accel/jerk values, cooling the Duet (drivers) adequately, and running typical motors near their rated current, most layer shifting is a consequence of either mechanical binding in your printer, wiring problems, or nozzle collisions with protruding plastic that is curling up for various reasons (eg insufficient cooling of corners). It’s actually pretty hard to make accel/jerk cause skipped steps without something else wrong with your printer or settings. There’s just too much safety factor in typical setups.

    Once you start legitimately pushing limits, typically you’ll hit a wall with some combination of your tolerance for ringing flaws, blobs/zits due to large extrusion rate changes, and the rate you can melt/cool the filament.



  • There are a lot of factors at play, as you can imagine.

    Here's some documentation that might give you some background basics.

    https://duet3d.dozuki.com/Wiki/Choosing_an_extruder_drive
    https://duet3d.dozuki.com/Wiki/Choosing_and_connecting_stepper_motors
    https://duet3d.dozuki.com/Wiki/Choosing_the_power_supply

    Basically, for 3D printing applications you'll generally be using NEMA17 motors. The Duet can use 24v power, which will help the motors hit to speed before torque starts to drop off. There are some calculators in there that can give you an idea of how a given motor might perform.

    If you're skipping steps and you don't feel like you're hitting high enough top speeds you may be using motors with too little torque and current limit on a 12v system. Upgrading to 24v might help. But really, even if you can improve high end travel speed, your actual print speed will be limited more by your extruder melt rate. Plus the fact that perimeter speed will be limited by the constant direction changes and loss of print quality when you go too fast.

    An E3D V6 has a melt rate of around 15mm^3/s. Maybe higher if you increase the temperature to the limit of your material.

    0_1537558153679_bf9d6a1d-2daa-402d-b5b1-779a719e0686-image.png

    A little simplistic, but it's ball park. And it's doable. I have printed PLA at 210c solid infill at 200mm/s with a 0.4 nozzle and 0.2 layer height on my CoreXY. I use lower acceleration (900mm/min) and more modest jerk (900mm/min) so that on short segments it never hits the top speed, but on longer sections it does hit the top speed. I usually do infill every other layer or some multiple of the perimeter layer height so it's thicker at 0.4mm or more, so half as fast, but it's printing it on fewer layers for an overall speed gain.

    So if moving faster isn't really going to shave off print time, you can also adjust the other variables in the equation. Wider nozzles move more plastic and allow for larger layer heights. A 0.6 nozzle and a V6 block are probably the sweet spot for layer height flexibility, extrusion width, and melt rate. Anything wider and you'd want a volcano block. I've seen from 30-40mm^3/s mentioned for the volcano. Which gives you a lot more headroom for speed, but it also comes with its own drawbacks. Increased ooze and stringing, bulges at corners, loss of XY resolution when using wide nozzles.

    0_1537558505494_f0b04d37-ea29-441c-9b1a-7a4fc4ca683d-image.png



  • @phaedrux Currently running on 24v but only 700mA. I have to do something cooling the duet before going higher on current.

    Motor specs:
    NEMA 17
    0.9° Step Angle.
    400 Steps Per Revolution.
    2.8V Rated Voltage.
    1.68A Phase.
    4.4kg/cm (61oz/in) Holding Torque.

    Running a full metal e3d with 0.4 nozzle only because I don't won't to sacrifice quality. It is not just minimising printing time but finding the actual limit of the hardware+software and go past it by improving it. I don't know in which way but I will definitely will.

    Thanks for the reference links!

    @RCarlyle thanks for the advice!



  • Personally, I think that if you are serious about printing at high speeds, then it comes down to how fast you can melt the filament. Furthermore, IMO the best way to achieve that is to use multiple melt chambers feeding in to a single nozzle. I did some experiments with 3 input Diamond hot ends which you can read about here https://somei3deas.wordpress.com/2017/06/22/exploration-of-print-speeds-with-a-diamond-hot-end/. There is an associated YouTube video in that blog too.

    My somewhat arbitrary conclusions were (among other things) 260mm/sec max using all 3 inputs with 0.5mm nozzle and 0.3mm layer height and 90mm/sec with a 0.9mm diameter nozzle and 0.6mm layer height. The latter equates to a melt rate in the order of 32mm^3/sec.

    You do get serious problems with pressure build up at those sorts of speeds but Duet pressure advance works really well in taming that, as per a later blog post here https://somei3deas.wordpress.com/2017/06/25/duet-pressure-advance-experiments/.


  • administrators

    @ckostikas said in Printing limits:

    Currently running on 24v but only 700mA. I have to do something cooling the duet before going higher on current.

    If it's a Duet WiFi or Duet Ethernet then you can go to more than double that current before you need to cool the Duet.


 

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