Saturday, 20 February 2016

This One Weird Trick will stop jams forever... or will it?

I've been looking at getting the E3D hotend (maybe even the Volcano, since I tend to print larger items rather than fine detail), but from a number of sources, including most importantly +nop head , heard that it's not so good for PLA. Plus I'd be unable to use my fan until such time as I may be able to print another.

On the other hand, I got a few tips, in particular a number of people had luck adding a bit of canola oil to the filament to grease the inside of the hotend slightly. Also, guitar strings are supposedly helpful, as is a bit of string with metal cleaner. I'm skeptical of the last one, as I don't know what it might leave behind.

Nop head suggests a 0.4mm (or probably 0.5mm in my case, as that's my nozzle diameter) drill shank while doing the atomic, I should get one. There's also the toothpick holder method, but I can't print the holder until my printer works:) Then there's "Korneel's Method" of carefully burning it with a kitchen torch and dipping it in alcohol. Not trying that one just yet.

After reassembling, when trying to center X/Y, I got "Printer stopped due to errors. Fix the error and use M999 to restart!.". Thank you for the informative error message. I tried turning it off and on again, as per IT Crowd. Worked. Sigh.

When extruding 5cm, it underextrudes quite a bit, but getting closer to the right amount, up to 3.7cm, then 4.5, then 4.725, then 4.7, then 4.8, then 4.4 (!), then 4.5. At this point I figured the difference might be due to too little tension on the extruder idler, so I tightened that. Results: 4.8, 5.1, 5.0. That's within my margin of error on this crude measurement, so I'm claiming it has gotten its problems out of the system.

An attempt at printing the test piece crashed into the bed, stripping up the kapton. Fortunately, I acquired some blue tape, which is a lot easier to apply. I did some proper levelling and calibration of extrusion (consistently extrudes 6% too little). After adjusting for that, I finally got correct extrusion. That was a lot of wasted filament there. The whole recycling filament idea seems more and more appealing. As part of testing, I extruded at 195C, at that temperature the PLA was drooling.

First test print (done without fan due to a short - I was lucky I didn't blow something) looked OK at the bottom but became increasingly stringy at the top. A sure sign of a jam coming on.

Maybe when I accidentally left it one high heat for a while I melted some of the interior and now it slowly builds up filament until it jams.

My coworker +Tom Riedl pointed out that the new hobbed bolt, being curved in its teeth, would move said teeth at different speeds, thus effectively carving out filament. My guess is that it doesn't carve enough to actually tear it off.


  1. You can't print PLA without a fan on after the first layer. There is a hole in the fan duct to keep the cold end cold. Without it heat will creep up the hot end until PLA goes soft in the entrance and jambs.

  2. I do have the fan mounted, though due to hacky wiring it does occasionally get blocked.

    I was able to print without a fan earlier, though the print quality was crap, but it didn't jam. Or maybe I didn't print for long enough at a time for jams to happen.

    I have some vague ideas about mounting the fan further away and using tubes to direct the air, leaving the hotend open to allow more airflow (and view). But not yet.