Idea for filament grip/release for respooled filaments?

[gtoal]

I had an idea for a new device just now, but I’m not a mechanical engineer so I’ll throw this idea out to those of you who are, in the hope that you can tell if it’s plausible and maybe sketch something like this up…

Imagine there is a channel in the hub of a spool. Fitting inside this channel are two slightly wedge-shaped pieces aligned facing the direction of the filament, but joined at the far end with a hinge. There is a gap between the wedges that is just narrower than the filament. You lie the filament between these flanges and push them down into the channel, where they hold the filament in place and allow you to wind the filament on to the spool without sticking it down with tape. When printing, once you are near the end of the spool, the filament is no longer being pulled tangentially to the hub, but away from it at a slight angle. This is enough to pull the flanges out of the channel, and as they are pulled out, the wedge shape causes them to relax their grip on the filament when can then safely disengage from the spool and be used without dragging sticky tape into the AMS.

I don’t think anything like this exists for 3D printing spools. I looked online for devices that could pull and release wires, but all I found were Kellem wire grips and I don’t think that design would work as an automatic-release filament grip in a spool.

I’ll try to sketch my concept below but I bet you guys can do much better…

The red part is the hinged gripper - the ‘legs’ are slightly splayed apart so that when it is pulled out of the channel, they spring apart enough to let go of the filament. Vertically, the legs (Maybe we can call them chopsticks?) taper towards each other so that when they’re in place, the final wrenching pull on the filament as the roll ends has enough pull to yank the end of the gripper away from the hub (but it doesn’t fall out because it’s attached at one end with a hinge of some sort) I guess this could be made as an add-on to a spool but ideally it would be built in to the spool itself. Is it a feasible idea? Has it been done already? I’ld love to hear some feedback from the engineers among us - I’m more of a software guy myself.

[protoboard]

NoTapeSleeve.step.3mf (110.8 KB)
Please note; this is a STEP file - REMOVE “.3mf” in the filename!
I made this for “TPU for AMS”.

[protoboard]

It has high friction along the tangent but low friction in the radial direction.

[gtoal]

Excellent take on the concept …no multiple parts needed, just a simple channel. I presume making it in TPU or similar is an essential part of this. I’m surprised that the object holds together like a solid when printed in TPU, I thought TPU was more flexible than that.

So this would slide over the hub in a Bambu spool? I assume you’ve sized it just right to hold tight to the hub and not rotate. (Oh wait, of course if it’s like the cardboard spools, you’ve added that notch which is what stops it from slipping… gotcha…)

I appreciate your work on this. Feel free to post it yourself. I’ll print one shortly and try it out. Thanks!

I’m wondering if the original respooling would go better if the channel were close to the edge rather than in the middle, i.e. to avoid a step-bump in the middle of the spool, but maybe that doesn’t matter…

G

[protoboard]

Let us know how it turns out! I used HARD TPU, (Bambu “TPU for AMS”). Only tested it a few times in the AMS but it works. Might even work printing it in PLA if you adjust the channel to pinch properly. Same size as Bambu cardboard sleeves.

[protoboard]

The channel is centered to have optimal angles when it runs out. It shouldn’t matter where you start spooling as it will always “step up” for each layer.

[gtoal]

Ah right! I thought you had just placed it there because that was what I’ld done in the original sketch, but I see you’ve given that some thought too I’m looking forward to printing one and giving it a try. And I just happen to have a small amount of leftover filament from the end of a couple of spools that I can do a real test with. (in fact it was because those spools were running low that I was thinking about this problem…)

[gtoal]

Oh! You’d already come up with this! ( I just now found that forum thread: Tape at the end of spool - #446 by protoboard ) Sorry, I thought you had quickly designed this in response to my post I must have sounded like a complete pillock when I said ‘feel free to post it’! Thanks for sharing.

[protoboard]

I haven’t posted it to Makerworld yet because I wanted to test it with a few more filament types first I remember one more detail: this is a section view, and it prints support-free with no overhangs when oriented with the notch facing up. Not sure how many people actually respool (I’m lazy so I don’t…), but I’ll share it for remix if there’s interest. Collective data is what really matters here!

[gtoal]

Frankly, I would go to the bother of respooling even an original Bambu spool just to avoid the end-of-spool tape hassle. Also (excuse me giving my own model a little plug) I hacked up a cheap & easy motor for the respooler I use, so it’s really not that much of a hassle: Autocrank (TT motor for Pasta Lite) by gtoal MakerWorld: Download Free 3D Models

[gtoal]

Well, I rather foolishly thought “I’ll make one in PLA even if I know it’s not going to be ideal…” so I did, and of course it was far from ideal! The rotational grip might be enough to allow respooling to start (it feels a bit slippy), but the filament is covered over too much to allow angled extraction at the end of a print run - it bends the filament at the entrance to the ‘tunnel’ part, but there’s not enough room for it to ease out vertically - has to be pulled back out the way it went in. So with PLA (which is all I have to hand at the moment), either I have to reprint it with a wider gap above the filament … or take a file to the channel and open it up manually

I was going to avoid the long print by slicing off everything except the relevant band round the middle in OpenSCAD (I haven’t worked out yet how to delete stuff in Bambu Studio - I can pull up a cube but don’t know how to resize it - haven’t needed to until now, since I usually do things like that in OpenSCAD, but OpenSCAD won’t import the STEP file…) So rather than mess around trying to make a PLA version work, I think I’ll just wait until some recent filament orders start getting delivered so I can try other materials. I’ll let you know when I make progress…

[gtoal]

I had a bit of a head scratch and decided to do a small test to see if a simple tapered channel in PLA could be made to work. Turns out it can - the deeper of the four test slots in the code below works quite well. I’ll map it on to a cylinder next. The slight taper serves two purposes - the obvious one, but also it removes any need for exact fine tuning of the slot for marginally different widths of filament - just push it in far enough to grip and you’re done.

$fn=20;
filament=1.75;
surface=5;
demowidth=20;
demolength=50;

module taperedCube(depth,
                   width2,d2,
                   width1,d1, 
                   length) {
  hull() {
    translate([-width1/2,0,-depth]) cube([width1,0.1,d1]);
    translate([-width2/2,0,-depth]) cube([width2,length,d2]);
  }
}

// Let's start with a flat surface and see how well we can grip...
module channel(depth, delta) {
  taperedCube(depth,
              filament-delta,depth+filament,
              filament+delta,depth+filament,
              demolength);
    
  translate([0,demolength,-depth])
    rotate([90,0,0]) cylinder(h=demolength,
                              d1=filament-delta, d2=filament+delta);
};

difference() {
  cube([demowidth,demolength,surface]);
  translate([0,0,surface]) sphere(d=2); // mark a corner to help understand the test results
  translate([demowidth*1/5,0,surface]) channel(0.5, 0.2);
  translate([demowidth*2/5,0,surface]) channel(1.0, 0.2);
  translate([demowidth*3/5,0,surface]) channel(1.5, 0.2);
  translate([demowidth*4/5,0,surface]) channel(2.0, 0.2);
}

[protoboard]

That’s right, I’ve also tested that. It adds the risk of unwanted pinching though and could also break the tip on some filaments. But, it would be a fair trade-off to ingesting tape in most cases.
Creep, in both the sleeve material and filament, is a real issue. If you exaggerate that and conclude that “everything will be loose” after a few weeks, the result would still be favorable: The last few turns on the sleeve will not be retractable by the AMS but it will print just fine.

[gtoal]

I hope so! And if repeated use of the same hub makes the grip a little slacker, the taper in the channel should automatically compensate just by pushing the filament in a little farther the next time. I haven’t printed it yet because I don’t have my micrometer to hand to measure the spool diameter, but I’ve hacked up most of what’s needed in OpenSCAD if you’re interested. I’ll see if I can send what I’ve got so far to you directly through this system and if not I’ll come back and add it to this post. Apart from entering the right dimensions, the only tweak I still need to make is to round off the top of the channel so that there’s a less sharp overhang.

[gtoal]

Well, after 9 iterations I finally have a design that works acceptably well in PLA. ( https://gtoal.com/OpenSCAD/grabber2-v0.9.3mf ) It relies on being a tight fit in an original Bambu spool and it takes a little bit of practice to find the sweet spot to pinch the filament in between the two halves, but it does work! I may be the only person to use it given that it’s a little fiddly to attach, but I will definitely be using this myself on all 4 AMS slots. (I suppose I should put together a short video to show how to use it. I don’t make good videos )
I got a slightly better fit by using .15 instead of .20mm layers but that doubled the print time and wasn’t worth the improvement.