RRF 2.03 pressure advance causes 20% overextrusion


  • Moderator

    @jschall I find Cura falls apart faster than super Slicer on thin walls. In Cura you're forced to use 2 walls. The master build of Cura has the option of trying to replace one of those wall passes with a travel move, but it rarely seems to work well. At least the gap fill in Slic3r has a lot more leeway with regards to wall thickness. It's true that on the really thin side the walls just don't get extruded at all, but it seems to be a lot more forgiving. Cura will print the thin walls but it's usually well over extruded.



  • @jschall
    have you watched https://www.youtube.com/watch?v=7W5pPm0lZDE? it mentions the problems with the titans.



  • @Phaedrux Cura has something called "compensate flow" and I think it reduces the flow on one of the two walls so that the total extrusion volume is correct for the wall thickness.


  • Moderator

    @jschall Yes that's the setting I'm thinking of. Doesn't it seem silly to replace a one of the walls with a travel move though? It's still taking the time to move around the entire perimeter it's just not extruding anything. Not very elegant.

    For best results it also wants you to use outer wall first, which means overhangs suffer in addition to the extra ooze from the empty travel moves.



  • @Veti

    Yeah totally agree.

    Bowden is fking stupid. The whole premise of bowden is to REMOVE a motor that needs to output LESS THAN 1W OF MECHANICAL POWER in order to SAVE MASS on something that weighs in at like 500 grams. Hey, here's an idea: how about instead of that, we stop using half-pound 1970s-era stepper motors?



  • @Phaedrux said in RRF 2.03 pressure advance causes 20% overextrusion:

    Doesn't it seem silly to replace a one of the walls with a travel move though? It's still taking the time to move around the entire perimeter it's just not extruding anything.

    Not really, because the only case where it isn't extruding anything is the case where the wall thickness is exactly equal to the line thickness. But yeah, could be optimized.

    What slicer does the absolute best with thin walls? I bought Simplify3D and was horribly disappointed. Cura so far seems to do the best job overall.


  • Moderator

    I'd say super slicer does a reasonable job. It seems to have the option to connect the thin wall to the other adjacent perimeters whereas prusa slicer treats the thin wall section as a separate extrusion path entirely.



  • @jschall said in RRF 2.03 pressure advance causes 20% overextrusion:

    @Veti

    Yeah totally agree.

    Bowden is fking stupid. The whole premise of bowden is to REMOVE a motor that needs to output LESS THAN 1W OF MECHANICAL POWER in order to SAVE MASS on something that weighs in at like 500 grams. Hey, here's an idea: how about instead of that, we stop using half-pound 1970s-era stepper motors?

    Here's a servo that outputs more torque than the geared titan extruder. It costs a whopping $10 - which is cheaper than the stepper. It weighs 58g vs 280g for the stepper. It includes the gears, which add not-insignificant mass as well. I'm not trying to say you can buy that servo and stick it on an extruder and it will work unmodified - it won't. I'm pointing out from a first principles point of view that you can cut out 80% of the mass of the extruder, without bowden, and it doesn't have to be expensive.

    https://hobbyking.com/en_us/hobbykingtm-high-torque-servo-mg-bb-w-proof-12-8kg-0-22sec-58g.html?queryID=76697295b4ca978c54e06a560255a667&objectID=47699&indexName=hbk_live_magento_en_us_products_hbk_price_stock_2_group_0_desc



  • @jschall said in RRF 2.03 pressure advance causes 20% overextrusion:

    @Veti

    Yeah totally agree.

    Bowden is fking stupid. The whole premise of bowden is to REMOVE a motor that needs to output LESS THAN 1W OF MECHANICAL POWER in order to SAVE MASS on something that weighs in at like 500 grams. Hey, here's an idea: how about instead of that, we stop using half-pound 1970s-era stepper motors?

    One could argue that the limiting factor on how fast one can print an object is how fast one can melt and extrude the filament. So if carriage mass isn't a limiting factor, then why reduce it? In fact I have demonstrated this by printing at up to 300mm/ sec with a moving carriage mass of around 2Kgs driven by modest NEMA 17s. I'll make a other contentious statement that adding mass reduces the resonant frequency - I don't get ringing -ever. So I'd say, if you physically have room to go direct drive, go for it and forget the mass. Unfortunately, it isn't physically possible to connect 6 extruders to a mixing hot end, so in my case, I mount then on a separate gantry above the hot end and use short Bowden tubes.



  • @jschall Can those servos meet the speed/acceleration achieved by a stepper? Not saying they can't I just have no idea of what they can do.



  • @gloomyandy

    i think the biggest problem is that they cant do a full revolution



  • @Veti said in RRF 2.03 pressure advance causes 20% overextrusion:

    @gloomyandy

    i think the biggest problem is that they cant do a full revolution

    On one hand, that shape of servo can be had in continuous rotation, on another hand, it’s not a servomotor, what is meant when some people say they want a servo on a CNC type machine like a 3D printer. Hobby servos are very limited on what they can do for that kind of use because the type of input doesn’t allow for the level of control needed. Hobby servos also use deep multistage gearboxes, which induce excessive backlash.


  • administrators

    This thread is long and getting hard to navigate. I think what is being said is that using RRF 3.1.1, a particular print causes 3% over-extrusion (it was more in earlier firmware). Is that correct?

    My suspicion is that this is caused by the firmware rounding pressure advance to the nearest microstep. If this is the case, changing extruder microstepping will affect the amount of over-extrusion. @jschall, are you able to test this? What extruder microstepping are you using at present, and what is the extruder steps/mm ?


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