Print speed slow and appear to have regular extruder speeds

  • Hi there,

    I have fitted a Duet Wifi to a home built Printer, she is finally operational, i yesterday did my first print, as can be expected there is still a fair amount of challenges and tweaking that lie ahead.

    Machine Info:

    2m X 2m X 2m Volume.

    NEMA 34;s and 20mm (2005) Ball screws used-1 for X, 2 for Y and 4 for Z.
    External 7.8A Drivers used for X, Y and Z. (Via Duet Break out board)
    Each stepper on its own driver.
    Titan Aero Extruder with Nema 17 stepper fed via E0 on duet. Volcano 1.2mm Nozzle.
    48Volt supply to external drivers.
    24V Volt supply to Duet and Extruder.
    Using S3D

    Operator, still a newbie but have been printing for about 6 years with great results;ts, this is however my first large scale printer, and also my first time using external drivers and Duet equipment.

    There are 2 items that I'm hoping i could get some advice on:

    The first is, Speed.

    In S3D, my print speed is set to 60mm/s, in my config.g speeds are set to 2.6m/min for X and 3m/min for Y, yet when printing small or large model max speed I can achieve is 11.4mm/sec.
    I up the speed to 200% on the Due but it stays at 11.4mm/sec.
    Cant help but feel that i have missed something in my Config.g

    2nd issue is extrusion, i admit that my bed leveling and offsets are not yet perfected, but the extruder-every 20-25mm seems to briefly slow down, the result is a rather inconsistant flow.

    If anyone that is able to assist is prepared to review my settings and check out my pics, I would be very grateful.

    0_1554303881224_WhatsApp Image 2019-04-03 at 17.03.52.jpeg
    ![0_1554303890142_WhatsApp Image 2019-04-03 at 16.59.41.jpeg](/assets/uploads/f0_1554303899739_WhatsApp Image 2019-04-03 at 16.58.16.jpeg iles/1554303894207-whatsapp-image-2019-04-03-at-16.59.41-resized.jpeg)

    My Config File is as follows:

    ; Configuration file for Duet WiFi (firmware version 1.21)
    ; executed by the firmware on start-up
    ; generated by RepRapFirmware Configuration Tool on Thu Mar 28 2019 12:12:45 GMT+0200 (SAST)

    ; General preferences
    G90 ; Send absolute coordinates...
    M83 ; ...but relative extruder moves

    ; Network
    M550 PDarnz Does 2m2 ; Set machine name
    M552 S1 ; Enable network
    M587 S"Darnz Wharehouse" P"Darnial#89" ; Configure access point. You can delete this line once connected
    M586 P0 S1 ; Enable HTTP
    M586 P1 S0 ; Disable FTP
    M586 P2 S0 ; Disable Telnet

    ; Drives
    M569 P8 S1 R1 T4:4:5:0 ; Drive 0 goes forwards for X
    M569 P7 S1 R1 T4:4:5:0 ; Drive 1 goes forwards for Y
    M569 P5 S0 R1 T4:4:5:0 ; Drive 2 goes backwards for Z1+2
    M569 P6 S0 R1 T4:4:5:0 ; Drive 3 goes backwards for z 3+4
    M569 P3 S0 R1 ; Drive Goes Backward for E0
    M584 X8 Y7 Z5:6 E3 ; Apply custom drive mapping
    M350 X16 Y16 Z16 E16 I1 ; Configure microstepping with interpolation
    M92 X80 Y80 Z80 E400 ; Set steps per mm
    M566 X2500 Y2500 Z1200 E1200 ; Set maximum instantaneous speed changes (mm/min)
    M203 X2600 Y3000 Z600 E400 ; Set maximum speeds (mm/min)
    M201 X100 Y100 Z500 E250 ; Set accelerations (mm/s^2)
    M906 X800 Y800 Z800 E1200 ; Set motor currents (mA)
    M84 S0 ; Disable motor idle current reduction

    ; Axis Limits
    M208 X0 Y0 Z0 S1 ; Set axis minima
    M208 X1800 Y1800 Z1800 S0 ; Set axis maxima

    ; Endstops
    M574 X1 Y1 S1 ; Set active high endstops

    ; Z-Probe
    M574 Z1 S2 ; Set endstops controlled by probe
    M307 H7 A-1 C-1 D-1 ; Disable heater on PWM channel for BLTouch
    M558 P5 H10 F300 T6000 ; Set Z probe type to bltouch and the dive height + speeds
    G31 P25 X-44 Y0 Z2 ; Set Z probe trigger value, offset and trigger height
    M557 X15:1835 Y15:1835 S600 ; Define mesh grid

    ; Heaters
    M140 H-1 ; Disable heated bed
    M305 P1 B4725 C7.060000e-8 ; Set thermistor + ADC parameters for heater 1
    M143 H1 S280 ; Set temperature limit for heater 1 to 280C

    ; Fans
    M106 P0 S0.3 I0 F500 H-1 ; Set fan 0 value, PWM signal inversion and frequency. Thermostatic control is turned off
    M106 P1 S1 I0 F500 H T45 ; Set fan 1 value, PWM signal inversion and frequency. Thermostatic control is turned on
    M106 P2 S1 I0 F500 H T45 ; Set fan 2 value, PWM signal inversion and frequency. Thermostatic control is turned on

    ; Tools
    M563 P0 D0 H1 ; Define tool 0
    G10 P0 X0 Y0 Z0 ; Set tool 0 axis offsets
    G10 P0 R0 S0 ; Set initial tool 0 active and standby temperatures to 0C

    ; Automatic power saving
    M911 S10 R11 P"M913 X0 Y0 G91 M83 G1 Z3 E-5 F1000" ; Set voltage thresholds and actions to run on power loss

    ; Custom settings are not configured

    ; Miscellaneous
    M501 ; Load saved parameters from non-volatile memory

  • @darnz What layer height are you using with that 1.2mm nozzle?

  • @deckingman
    Hi, 1st attempt was at 1mm
    2,3rd and 4th attempt at 0.8mm

  • @darnz
    OK. Doing some very rough calculations, with that diameter nozzle and those sort of layer heights, I'd say that your extrusion rate is about 60% of the carriage speed. Now 11.4mm/sec for the carriage multiplied by my somewhat arbitrary figure of 60% shows that the extruder will be running at about 6.84 mm/sec. A quick look at you configuration file shows that you have the maximum extruder speed set to 400mm/min which funnily enough is 6.7mm/sec. Therefore it's fairly reasonable to come to the conclusion that your speed is being limited by the maximum that you have set for the extruder, so you need to set that much, much higher.

    The next problem you will face is that the speed you are able to print at will be limited by how fast you can melt the filament, but that's another matter altogether and has nothing to do with configuration settings. Having said that, it is probably the answer to your second question.

  • @deckingman

    Thank you for that!
    Very helpful! And makes perfect sense!

    Have a super volcano on order as I suspect I will run into problems trying to keep up with the flow.

  • @darnz Look at it this way. With a 0.4mm diameter nozzle and layer height of 0.3 mm, a 1mm long filament bead with have a volume of about 0.038mm^3. On the other hand, with your 1.2mm diameter nozzle and 1.0 mm layer height, the volume of a 1mm long filament bead would be about 1.13mm^3. That's almost 30 times greater. So you will be extruding about 30 times more filament than with a 0.4mm diameter nozzle and therefore the maximum carriage speed you could expect to use would be 1/30th of the equivalent speed using a 0.4mm diameter nozzle.

    The super volcano will help, just as it would with a smaller nozzle.

    Oh and you need masses of cooling air to cool the part. That kind of volume of molten filament takes a long time to cool (I know this from experience).

  • So I Upped the max extruder speed and was able to achieve much greater speeds.

    I did find that at just 30mm per sec, the extruder started to grind at the filament.

    I don’t think that the standard heater cartridge and hot ended can deal with this kind of volume.
    You mentioned making use of a smaller nozzle, I wondered if you had any advice for my current setup? Can I do anything to increase amount of flow
    I did experiment with various temps, but again, at 30mm it starts to battle to keep up.

    For now I am going to fit a smaller 0.8mm nozzle.

    I really just have the Aero on to see what this build can do.

    I will soon be fitting a pellet extruder.

  • @darnz Well as you have discovered, ultimately the print speed comes down to the volume flow rate of molten filament and that in turn is entirely dependent on the melt rate. If the extruder was grinding the filament at 30mm/sec then it's a reasonable bet that you started to get under extrusion caused by insufficient melting at about 25mm/sec. So assuming you used a width of 1.2mm and a layer height of 0.8mm then the volume flow rate is about (1.2 x 0.8 x 25mm/sec) = 24mm^3 / sec which is actually quite respectable for that type of hot end.

    Now if you fit a 0.8 mm nozzle, the layer width becomes 0.8 and say for example that you used a layer of 0.6mm, then you carriage speed could be increased to (24/(0.8X0.6)) = 50mm/sec. But the print time will be more or less the same because you'll have more layers and each layer will be made up of more individual strings. Depending on the object geometry, it might actually take a bit longer because you'll have more non-print moves

    Increasing the temperature should give a higher melt rate so should allow you to increase the print speed a bit (but not much). Beyond that, it's all about the laws of physics.

    The melt rate is a function of temperature, surface area of filament that is in contact with the hot surface, and time. We can't do much about temperature without degrading the filament. Which means we have to concentrate on surface area and time. If you have a single melt chamber fed by a single extruder, for any given speed there is nothing you can do to increase the time that filament spends in the melt chamber, so the only thing you can do is increase the size (or more precisely the surface area) of the melt chamber. Which is essentially all that E3D do with their Volcano and variants thereof.

    In my opinion, based on a lot of work that I have done, a better method is to use multiple melt chambers fed by individual extruders. Using something like a 3 colour Diamond mixing hot end, this give two things. Firstly, you triple the surface area of filament that is in contact with the hot surface because there are 3 melt chambers. Secondly, for any given flow rate from the nozzle, each individual filament moves at 1/3rd of that speed so you also triple the time that the filament is contact with the hot surface.

    Using that technique, I have been able to print at 100mm/sec using a 0.9mm nozzle with 0.6mm layer height before under extrusion became apparent. That equates to a volume flow rate of about 54 mm^3/sec. You can read more on my blog here

    I have no idea how pellet extruders perform with regard to melt rate so would be very interested to know your findings.

  • You can find the max flow rate for your hotend using a simple test and a formula. Then you can use those results in another formula to determine viable combinations of layer height, extrusion width, and print speed.

    Max Flowrate = Max Input Feedrate * pi * (Filament Diameter/2)2
    To find the Max Input Feedrate, assuming your extruder steps per mm is calibrated already and your heater PID tuned, you'll need to bring your hotend to the temp you'd normally wish to use for that material and start extruding some plastic. Start at 1mm/s and extrude 50mm, then increase it by 1mm/s and extrude 50mm again. Repeat this until you can see or hear the extruder start to skip steps. Back off the speed by 0.5mm/s until it stops clicking and try to extrude 100mm of filament at that speed. If it can keep up, you've found your max flow rate.

    So in my case, with a V6 hotend with 0.6 nozzle and 40w heater, I can extrude PLA at 6mm/s at 210c using filament measured at 1.71mm. Using the formula I get a max volumetric flow rate of ~13.8 mm^3/s. This is the volumetric limit of the hotend. This will be somewhat dependant on the material and temperature used, so feel free to try different temps and materials to see how they compare. I find that the ballpark is pretty inclusive of many filaments. To be on the safe side you can back off your max flow rate by 10% for a margin of safety.

    I'm going to guess that you're not really successfully melting properly at the rate that @deckingman suggests above. 24mm^3/s for a V6 would be far beyond what you could really expect. I think the very wide nozzle is playing a part there because even though the plastic isn't fully melted, there is very little back pressure to cause it to skip. I would guess that your layer adhesions would be very poor. E3D suggests that you may be able to get a reliable melt rate of between 10-15mm^3/s based on temperature and material. My results fall in the middle of that range so it would seem to agree.

    Using this result you can use the following formula to find your top speed based on the extrusion width and layer height you want.

    Max Suggested Speed = Volumetric Limit / ( Layer Height * Extrusion Width)


    So using that we can see a suggested print speed of 13mm/s, which is not exactly fast, but it's as fast as your hotend can reliable supply the volume of plastic requested. And as you can see, even though you could print at 54mm/s with the 0.6 nozzle, it's still limited by the melt rate, which is really the true speed of your printer. Using a volcano or super volcano greatly increases the volumetric limit and allows for large nozzles and faster print speeds.

    I'm also very interested in seeing your results from the pellet extruder. From what I gather the flow rate can be quite high, but the system is very laggy.

    If you want to play around with the excel spreadsheet I use to calculate all these things more easily if can be found here:

  • @phaedrux My calcs were very much "back of a cigarette packet" because I had to guess the layer height and the only clue I had about when under extrusion occurred was the Op's comment regarding the point where the extruder started to grind away at the filament. So the number I came up with was only useful in order to calculate what carriage speed might be possible with a smaller nozzle.
    Your method would indeed give a better indication of the true melt rate.
    For info, if you take a gander at the blog post I linked to, nozzle diameter does indeed play a significant part in all of this but in my tests, I had only had 0.5 and 0.9 to choose between. So it would be interesting to use your method with a much wider range of nozzle sizes to determine the exact relationship between nozzle size and volume flow rate. My gut feeling is that there will be a point at which further increases in nozzle diameter have no effect on volume flow rate. In my case, with my hot end, it could be greater it less than 0.9 mm. I have no way of knowing without buying a range of Diamond hot ends which would be really expensive.

  • Many thanks, I will run these formulas today.

    I think I will try them both on current 1.2mm nozzle as well as a 0.8mm

    I really appreciate you detailed input and advice!

    Thank you very much!


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