Fancy Filament Joiner Has Promise, But Ultimately Fails

[Proper Printing] has been trying to 3D print rims for his car for quite some time. However, the size of the print has led to problems with filament spools running out prior to completion. This led to endless headaches trying to join several smaller lengths of filament in order to make a single larger spool. After his initial attempts by hand failed, a rig was built to try and bring some consistency to the process. (Video, embedded below.)

The rig consists of a heater block intended to melt the ends of two pieces of filament so that they can be fused together. A cheap set of brass calipers was modified with a tube in order to form a guide for the filament, ensuring that it gets bonded neatly without flaring out to a larger size. Fan coolers are then placed either side of the heating area to avoid turning the whole filament into a hot mess.

Unfortunately, the rig simply didn’t work. The initial design simply never got the filament hot enough, with the suspicion being that heat was instead being dumped into the calipers instead of the filament itself. Modifications to reduce this sadly didn’t help, and in the end, more success was had by simply holding a lighter below a length of brass tube.

While the project wasn’t a success, there’s still value in the learning along the way. We can’t see any fundamental reason why such a rig couldn’t be made to work, so if you’ve got ideas on how it could be improved, sound off in the comments. We’ve seen other successful builds using hair straighteners in a relatively simple setup, too.

[Thanks to Baldpower for the tip!]

28 thoughts on “Fancy Filament Joiner Has Promise, But Ultimately Fails

  1. Maybe a gap between the alignment tube, with a hot blade in contact with filament, blade retracts then both ends of the filament pushed together, shear off resulting bulge, similar to joining round rubber belts available many moons ago or welding bandsaw blades currently.

        1. The potato-gun strategy!

          I doubt PLA would survive that, it’d be a lot of force and the filament is pretty brittle. Maybe you could chip away at it bit-by-bit, with a series of blades, and end up with a polygon that’s close enough to a circle to work?

    1. You can pause the print and use the move command on Marlin to move the hotend away, switch the filament, prime it, and once it’s ready, move it back to the spot it stopped at and resume the print.

    2. I just pause the print. I did have to uncoment something in the Marlin config to get that feature. I also think I remember playing with my slicer settings in order to get it to always return to where it left off after the pause. Something with absolute positions vs relative movements, something like that.

      Anyway, I can have the 8-bit typical non-touch LCD w/ a rotary encoder and Marlin menus that are so common. There’s an option to pause. If I pause the extruder goes up a few centimeters in Z and homes X,Y. Then I can change the filament and select resume. Or, more commonly I press pause in Octoprint which does the same thing.

      It’s also a way that you can change the color mid-print.

    3. Most people just pause print, load new filament and press go. There are even “filament-end” detectors, you can typically just wire some lever to your board and it will pause or execute some script when your filament runs out. Splicing filament is only useful if you want to leave your printer unattended for several days.

    4. Prusa will stop when it runs out of filament, you just feed in the next spool and continue. The problem I have more often than not is the filament is attached to the spool, so it doesn’t run out, it just jams.

  2. I’m pulling my yikes face. Injection moulded simple plastics are not used commercially for automotive wheels, BASF came out with a fiber reinforced injection mouldable plastic and there were older versions like the Shelby Dodge “Fiberide” wheels, which IIRC had hand laid fiber in them.

    What I’m saying is that if plastic wheels need tweaks to the injection moulding process to make them work, FDM printing is never going to be strong enough to be safe. Well at least not with a cool looking wheel that’s light, you can compensate with bulk until you’ve got a heavy POS. Please tell me he’s doing this to lost PLA cast them in metal, coz aside from strength, he’s gonna have huge porosity and sealing problems. Oh damn, also heat is a huge issue, FDM plastics are gonna have the studs pulling out of them with a few hard brake applications. I wouldn’t even trust them to hold the car up sitting on black asphalt on a hot summer day.

  3. This is a pretty interesting project just because at first glance, it seems simple, but then all the details hit. Keeping the heat where you want it has been solved pretty elegantly by e3d with some great thermal simulations to get the design right, followed by lots of real world testing, so the idea of a thin segment of poor heat conducting stainless steel is tried and true.

    E3D heat breaks have the benefit of not needing to be split in half though, so a simple thread joining to an aluminum block is an easy way to go. They are also going into a nozzle, so tolerances can be relieved a little. Needing to be able to get the filament out, properly sized with no seams, pretty much means needing to break the “mold” in half. Now we start getting complicated. Initial thought is to just bond the stainless half to the aluminum with JB weld, however, that’s a poor heat conductor into a poor heat conductor…Not great. Also, JB Weld does have a max service temp….and I seem to recall it not being very high. So I think I’d oversize the stainless a bit to allow for some threaded holes (doesn’t need to be big screws, and can be a fine pitch thread to reach full strength without a lot of depth) to retain the stainless part to the aluminum. It tolerances are held tight, heat conduction will be very good. This system could be used to join PEEK, as its all metal. The last thing I think I’d to is add a place for a thermal sensor, as close to the stainless part as possible, and as far away from the heat source as possible to have a good idea of when the plastic was melted. The only real downside to the approach is the larger stainless section. I would think that to be a small tradeoff. I might have to try it just for fun.

  4. You can buy filament on larger spools than the normal 1kg ones, FWIW.

    And like @morbidpete says, there are a number of filament fusers on the market which do this whole process automatically, I’d think how to do it is a solved problem. While I respect the DIY attitude, it’s still useful to do research on problems first. Sure sometimes reinventing the wheel leads to amazing innovation, but normally it just leads to wasted time and incompatable solutions.

    1. Well it would be less worrying if they did blow up at the air pump, that’s not the test really, and if it does, it’s a lucky escape. Getting something to hold up to 35psi is easy, getting something to hold up to the 60psi it might hit on a hot day, higher speed, longer duration, highway run is not, never mind the probable 120psi spikes you get when you hammer a pothole. Oh and fun thing, when it got warmed up all the way on the hot highway run the stiffness modulus dropped 10%, even if we’re still the right side of glass transition onset cliff.

      1. Indeed, I have serious doubts you could use FDM to achieve this directly no matter how much bulk the design has. Some 3d printed elements to a wheel still containing steel? structural elements in key areas is still a bad idea, but at least much more plausable – Think wire wheels – the wires can’t hold individually, not even close but the collection of them constrained by the rim does with ease.

        For a pure FDM :
        Holding the pressure and weight maybe, especially if you give it a thin wrap of impermeable tape/wrap type stuff or an innertube so the gaps around layer lines won’t just let it all leak away.

        But as thermoplastics are never great conductors of heat (as they prefer to soften/melt over conduct) just having lots of mass won’t stop or even slow the outer edges of the print getting warm just from rolling the wheel, toss in applying the brake in close proximity you are just asking for it to warp and toss the tyre (or worse) under the load.

        Plastics also frequently creep rather badly under sustained load, so even while static the weight on ’em will turn them oval in short order I’d think..

        Then you have to consider the spike loads, on a perfectly smooth road under the right conditions maybe it could work, but braking, acceleration and cornering shifts the weight and even a small shift when the total weight is over a ton will really matter on such small structures, add in the potholes, speed bumps and that odd loose rock and its always going to fail. Even the vastly stronger than a purely FDM print could hope for Steel wheels don’t always survive a bad pothole… So I’d bet they are busted as soon as the road pressure is focused on that single point no matter how slowly traversed, or minor the pot hole…

        1. I don’t think I would want to try to use molasses bombs for hunting. I prefer my meat less mangled and unsweatened. I’m also not quite sure how to use them in competitive sport as they would pretty much always hit the target regardless of accuracy. And for self defense well.. if the attacker is far enough away that the molasses bomb shrapnel won’t also hit the defender then it isn’t really self defense is it?

          Nioe troll though!

  5. I think this is cool but doesn’t a working product exist already with the Mosaic? Also for giant prints you can get giant spools or better yet set up a pellet system. Al
    I wouldn’t recommend FDM for car rims just because of the material properties but still give this dude a B+ for effort… 😂

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