BMG CLONE extruder issues



  • I have a chinese BMG clone extruder and have a severe clogging issue with the filament feed gear hob.
    Here is the end result - a nice model to start (cleaned out the feed gear yesterday) and everything prints nice for about 4 hours when everything turns to crap.

    IMG_20200525_154839632_HDR.jpg

    Here is the feed gear when I inspected it - remember I cleaned it yesterday so this happened in 4 hours of printing

    IMG_20200525_155635830.jpg

    There was nothing unusual about feed speed, number of retractions, tension from the spool that required extra push or resistance to feeding (hot end was also cleaned yesterday)
    There are four questions I would like to raise:

    1. Cleaning feed gears seems to be a pretty standard maintenance but not after 4 hours of printing time.
      Do REAL BMG extruders suffer from the same issue or are the grooves maybe cut different or what?

    2. This seems to happen after I changed to this particular filament. The previous filament from the same manufacturer but black instead of white did not seem to suffer from this issue.
      Has anyone experienced this happening with one filament but not another ?
      I will probably switch back to black and run the same print and see what happens.

    3. In the second picture (the gear picture) you can see that only the primary hob is plugged up. The secondary, driven off the primary, seems to be totally clear (a quick blow cleared loose bits). Is this normal functioning or should I see both hobs plugged up? The filament, as fed in, is closer to the primary then the secondary hob.

    4. Is there anything that can be done to prolong the maintenance interval ? Would, for example, lubricating the filament with a vegetable oil soaked pad at the extruder input help ?

    Any thoughts ?



  • @jens55
    Have a look her:
    https://forum.duet3d.com/topic/14846/strange-blobbing-on-layer-change/20
    Check the diameter of the filament and the path...



  • Usually it is unrelated to the extruder. First test - slice that without any retraction and see if it works ok. If not, get the temp 10C up and try again, without retraction, usually at this point it works ok. Now start increasing retraction bit by bit till you start getting issues again. BMG and BMG clones can push filament pretty hard but if your filament swells and blocks due to it getting hot in the heatbreak the force needed to push it trough is greater than structural strenght of the filament itself and it will grind, buckle, break but you will not push it trough.



  • Thanks Arhi, I will give that a try.



  • I am now printing with retract off but I still get retraction from the pressure advance setting. I have also increased temperature to 235C which is up 15C (PLA) from before. Time will tell ...
    I have found a spot on the filament that was quite chewed down - it might have stopped for whatever reason at that point, loaded up the hob teeth and then sort of carried on with the occasional bit of feeding. I will see what the outcome is on this - it's a 20 hour print 🙂
    I also turned off the fan (was at 60%)



  • @jens55

    What is your LA setting? LA normally does only retract when using very high values (long bowden setup).

    I also think the filament got stuck somewhere on the way to the gears which then grinds the filament down.

    Too high PLA temps could also force heat creep (clogged extruder) which then also grinds the filament down.



  • LA setting ????? If you mean PA as in pressure advance then yes, I have a VERY long bowden tube (around 800 mm) and a PA setting of 1.0



  • @jens55 If the issue is due to heat creep at the hot end, then raising the temperature might make matters worse. I used to get similar issues with a Diamond hot end and Titan extruders and found that printing at the lowest temperature that I could get away with helped.
    Genuine BMGs use hardened teeth, and those teeth are much deeper than the clones that I have seen. So they grip the filament much better than the clones. Never had any issues with my 6 genuine BMGs. Just saying...



  • @jens55 You might also find these links of interest

    https://www.bondtech.se/en/2020/01/31/original-bmg-vs-clone/

    and

    https://somei3deas.wordpress.com/2018/05/11/bondtech-bmg-vs-e3d-titan-extreme-retraction-torture-test/

    The last one is an extreme retraction torture test I did back in May 2018 comparing an E3D Titan and a "genuine" BMG. The Titan ground through the filament somewhere between 7,000 and 8,000 cycles. The BMG was still going strong after 23,000 cycles. There was no sign of any grinding away of filament inside the BMG after 26,000 or so retractions whereas the Titan had lots (and a few bits of bearing).



  • @jens55 said in BMG CLONE extruder issues:

    I am now printing with retract off but I still get retraction from the pressure advance setting.

    the idea of that test is to see if without any retraction it will block or not, so it would make sense to turn off PA too. The quality of the print will for sure suffer during this test but it should not block.

    Then you need to figure out why it blocks with retraction - usually a poor heat break or poorly cooled heat break is the reason. I have to say most clones of e3d I seen have heat break that just can't handle real life situation ... also, ppl swap good fans with quiet ones, on the small scale that's used for extruder cooling low noise == low air volume being moved == shitty cooling

    as Ian said, dropping temp helps with heatcreep, increasing print speed usually also helps with heatcreep, better cooling of the extruder helps with heatcreep but mostly good design of the heatbreak and cooling is what solves the problem



  • Try one was a failure after about 4 hours of printing... try two is on the go but with pressure advance reduced to 0.5 from 1.0

    I will try and see if that works prior to turning PA completely off. There are still small retractions at this setting.



  • @jens55

    Yes I meant PA. LA is a bad Marlin habit from the past 🦆

    I don't think it has been asked before but what is your retraction speed? Too fast and the gear may also grind through the filament.



  • @Argo, it was 30 mm/sec but of course is turned off now.



  • @deckingman, yes, I did read your report re the BMG's when I first tried to look for answers.
    Hardened teeth isn't an issue, they grip just fine and I do not use abrasive filament. I can however see a possible issue with the particular cut or smoothness of the grooves. I would just like to eliminate all issues before I spend over $100 (CDN) for mostly a piece of plastic ... especially since this is the first time I have seen the issue.

    The hotend is a clone Chimera with (clone) Volcano nozzles but only one nozzle heated. The heatsink is warm to the touch but only around 40 or so degrees.



  • @jens55 even the original chimera had issues with retraction 😞 you had to really fine tune it to work ok, and that's very precisely machined piece of kit, the clones I tried are useless the contact between heatbreak and the heatsink is bad, you have to use a lot of good silver paste and they still don't cool the heatbreak enough, 40C on the heatsink can easily be 60+ on the heatbreak and it will block your PLA. The heatbreak itself is a totally different story, the ones I tried (and I got bunch as I purchased some chimera, cyclops and kraken clones to do some testing) the inside is not smooth at all.. originally I was thinking that getting just original heatbreak + nozzle from e3d and PRC made heatsink and heatblok will get it done but heatsink block is also poorly machined so the contact between heatsink and heatbreak is "2 lines" instead of a surface... it works ok for pushing filament in but as soon you start retracting it quickly heat up and block

    there are many different clones of BMG (some very good quality, many not really) but I have never seen a good clone of chimera/cyclops/kraken as you really need those machined precisely and you can't do precission milling cheaply, not even in china



  • <sigh> ok, understood.
    I will carry on testing to figure out what is going on.
    Before changing to the white filament I had nowhere near the amount of trouble so at this point I am still suspicious of the filament.
    My next step will be to switch back to black and try that while drying (just in case) the white filament.



  • @jens55 said in BMG CLONE extruder issues:

    @deckingman, yes, I did read your report re the BMG's when I first tried to look for answers.....................

    It was the two pictures at the end of the post that I wanted to draw your attention to. https://somei3deas.wordpress.com/2018/05/11/bondtech-bmg-vs-e3d-titan-extreme-retraction-torture-test/
    Especially the one showing the inside of a genuine BMG after 26,000 plus retract/un-retrcat cycles. The other one shows the inside of a genuine E3D Titan under similar (admittedly extreme) conditions. Both extruders appeared to grip the filament just fine but the pictures speak volumes.

    Edit. So while the clone might appear to be gripping the filament just fine, the reality might be somewhat different.



  • @jens55 might be worth tweaking the temperature (particularly if the black filament works better). I know some filament brands say that black requires a slightly higher temperature than other colours.

    I also second what the others have said about genuine components. I have a homebuilt printer with 700mm bowden. Originally I fitted a cheap cloned titan extruder, cloned V6 hotend, and poor quality PTFE tube. It just about worked but needed a lot of tweaking and I often had filament grinding etc. I now have upgraded to a genuine BMG, e3D V6 and capricorn XS PTFE. I cant say which was my original problem, but the system is so much better for using proper parts. Particularly with a long bowden, I think a lot of different factors can play, and several small gains can combine and add up to a lot performance improvement. That and a bigger credit card bill! 🙂 sorry it might not be news you'd hoped for...



  • @deckingman, I had seen the pictures but obviously didn't examine them close enough. My extruder looks like the Titan on the inside, full of bits.
    I have come up with another possible explanation of what is going on. It will require more testing before I can give more details.



  • @jens55 said in BMG CLONE extruder issues:

    Hardened teeth isn't an issue, they grip just fine and I do not use abrasive filament. I can however see a possible issue with the particular cut or smoothness of the grooves. I would just like to eliminate all issues before I spend over $100 (CDN) for mostly a piece of plastic ... especially since this is the first time I have seen the issue.

    You can save some money by just buying the original drive gear kit from bondtech. Genuine resellers in your area might have them available as well.



  • @engikeneer, the only thing 'original' I use is Capricorn tube 🙂

    I will work this out one way or another and if an original BMG is required for reliable printing than so be it. It's only cash ...... and the grief and aggravation of all the failed prints is causing the few hairs I have left to go gray.



  • @oliof, while it had occurred to me that I could just buy the drive gears, I think I will always wonder what I am missing by not using the full product. If things didn't work for some reason or other then I would have no real answer if the original parts are better than the cloned parts.



  • @jens55 correct, you would at least want the shaft gear and the POM gearwheel as well, and then the internal geometry of the clone could still be detrimental to filament path etc....



  • The old adage comes to mind - "Buy cheap, buy twice".



  • @jens55 said in BMG CLONE extruder issues:

    what I am missing by not using the full product.

    Long time ago I understood the "I'm not rich enough to buy cheap things" but still from time to time I go and purchase a clone. And EVERY SINGLE TIME it cost me so much time and nerves and ... every time I ask myself wtf I did it.


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