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Thread: Universal Hub

  1. #51
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    Nov 2016
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    Time for this thread to make it back to the top.

    Today I went in and made a small improvement to the universal hub.

    These cartridges were redesigned to simplify universal access with many filament feed solutions. Original spool, external spool, or mini-spool are all supported with the universal hub efforts.

    One mode, the internal spool, requires removal of the spool itself from the cartridge to refill it. That one mode of operation requires the removal of the tube coming from the filament driver mechanism. If the barrel nut was in place, then the tube could not be removed... and as you know, I can't stand that barrel nut to begin with. So the solution is to have a snug fit of the tube in the bulkhead. This means the tube is just held in the driver and can easily be removed without removing the driver mechanism itself. This is doable without too much issue but you will find that these tubes will be drawn back onto the gears from time to time and gets some chew marks on them. This has not affected the performance but replacing the tube when you put a new spool in can slow you down a bit. Just to review, the tube wants to be really close to the gears so that feeding new filament doesn't just collapse the tube. It is inevitable that the ends will wear but the feed has always worked flawlessly.

    Another thing you will notice with stock tubing in any configuration, including the B2B universal hub, it squirms! Meaning that under pressure, it will deform changing pre-loading the filament. Not so bad considering this is what the printer was finally dialed to manage. The entire stock bowden tube stretches significantly during operation. We got in the way of that!

    Now to go to overdrive on the design side... a quick review of what could be done if you have the tools to do so.

    I really wanted to protect that feed functionality. However, a rigid tube from the driver's gears to the appropriate depth in the bulkhead won't let you assembly the cartridge. The two ingresses are simply too deep to deform the case making the connection. So I considered another solution:

    Driver mechanism with solid feed guide.


    The aluminum tube is a K&S aluminum tube #83060 often available at hobby shops and hardware stores. It is .1875" OD and a .049" wall thickness. This leaves a nice over-sized center ID of just over 2mm which matches the stock Teflon tubing. As a matter of fact, it easily passes the bicycle spoke test... and the threads on the end of the spokes can be used to ream and descale the center. This will help ensure that the ID doesn't collapse when you make the bends and smooths the ID. Making this a permanent member makes the ingress of the remaining tube more manageable by shortening the reach.

    The second part of the tube that is machined to 2.9mm to fit in the bulkhead. The depth into the bulkhead is .57". The mechanism side OD reduction is only about .18" long. Depending on the mechanism you use; machined V. cast, the ID may varies. I like the cast mechanism for this because their opening is nearly 1/8" where the machined version is only 2.9mm. Either will work, but the remaining wall thickness will be further reduced. Bends in the tube were accomplished with a small hobby vice. If the whole thing can be put in place and relaxed as shown below, you got everything lined up correctly. As a note; the thick part of the tube is 2.75" long. Add it up; .18+2.75+.57=3.5" total length before bending operations.

    Relaxed fit test:


    Just for fun I ran the lathe across the entire length. Obviously not required but it gives you options to thin things up if you prefer.

    Again, remember, we are trying to remove the tube to remove and replace the internal spool without removing the mechanism from the case. And... we are making sure that when we do remove the spool, we don't collapse the stock tubing because there simply is no way to remove the spool without risking damage to the PTFE feed tube.

    Closeup of "the system";


    Once you are ready to button up the system, you will deforming the case to plug the end of the tube into the mechanism's receiving hole. This is quite a bit easier than making sure the PTFE tubing is fully seated before putting the thicker tube over it and pushing on the snug bulkhead. in this case, the bulkhead doesn't need to be snug. This is a foolproof solution.

    Case deformation will let you plug this into the driver mechanism;


    There is the other benefit in the fact that you've just saved yourself 99mm of original PTFE tubing for B2B nozzle solutions.
    And the larger Teflon OD tubing can be used for many more circlips for the grooved bowden tube.

    More options is a good thing


    This is certainly not the only means to accomplish this. Bottom line, this is just another fiddly bit that can be accomplished with these cartridges. I've made something similar with brass tubing. With this 2-piece solution, the spool removal will be even easier. You can make the short tube by soldering some wire around the tube to keep it where you want it instead of machining something. The second, longer tube will be trapped and has no place to go once the cartridge is re-assembled. I suggest finding 3mm OD brass tubing since the 1/8" tubing has a larger ID meaning a much thinner wall to make it work. And of course, the small segment could be machined from solid stock without too much additional more effort.

    If you want to hybridize this solution, it is certainly possible. Consider the short piece for your mechanism in metal but the remaining tube to be the stock PTFE tubing with the heavier PTFE sleeve. In this case, the short intrusion on the mechanism side could pop the tubing out during printing and get stuck in a compromising condition. Instead, make the short insert with a counterbore on the exit end to receive the PTFE tubing (Dia 2.9mm). You can get another .20" of ingress this way.
    This longer PTFE tubing being flexible and the additional ingress depth is not a problem with assembly. The point of doing this is to prevent manage to the end of the tube so it doesn't get chewed up in the driver mech.

    Let me know if anything requires clarification. Every upgrade is meant to make the Cube3 even more usable. Happy Printing!

    - - - - - - - - - -

    Cartridge "POP" tool.

    If you've been taking apart Cube 3 cartridges, you know there is a little difficulty in releasing the latches near the filament driver.
    I've stated in the past I've sharpened an unknown tool to get into the rectangular slots to release the two tabs at the "bottom" of the filament driver.

    Well, I got a few gifts with the Arduino Nano's I've been ordering.
    Decided to see if I could re-purpose one of them...


    Sure enough, a simple and sufficient mod to a small blade screwdriver is all it takes.
    Use this when you have most of the perimeter latches unhooked then popping these two center latches will finish the job.


    A quick grind or filing off to get a semi-sharp edge will let you get behind the little tab to release it.

    ...and it doubles for a filament trimmer by pushing the edge into the filament where you want to cut the filament and it also helps wind the filament through the bowden tube.

    One tool is doing it all now
    Last edited by TommyDee; 04-14-2019 at 08:28 PM.

  2. Thanks bolsoncerrado, buddybu thanked for this post


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